Informix Guide to SQL: Syntax

Informix Guide to SQL
Syntax
Version 7.2
April 1996
Part No. 000-7859A
Published by INFORMIX® Press
Informix Software, Inc.
4100 Bohannon Drive
Menlo Park, CA 94025
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ii
Informix Guide to SQL: Syntax
Table of
Contents
Table of Contents
Introduction
Products Covered in This Manual . .
About This Manual . . . . . . .
Organization of This Manual . .
Types of Users . . . . . . .
Software Dependencies . . . .
Demonstration Database . . .
New Features of This Product . . .
Conventions . . . . . . . . .
Typographical Conventions . .
Icon Conventions . . . . . .
Syntax Conventions . . . . .
Sample-Code Conventions . . .
Terminology Conventions . . .
Additional Documentation . . . .
Printed Documentation . . . .
On-Line Documentation . . .
Related Reading . . . . . .
Compliance with Industry Standards
Informix Welcomes Your Comments .
Chapter 1
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3
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16
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29
30
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1-6
1-9
1-12
1-16
1-18
1-19
1-22
1-43
1-46
1-77
SQL Statements
How to Enter SQL Statements . .
How to Enter SQL Comments . .
Categories of SQL Statements . .
ANSI Compliance and Extensions
Statements . . . . . . . . .
ALLOCATE DESCRIPTOR. .
ALTER FRAGMENT . . . .
ALTER INDEX . . . . . .
ALTER TABLE . . . . . .
BEGIN WORK . . . . . .
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CHECK TABLE . . . . .
CLOSE . . . . . . . .
CLOSE DATABASE . . . .
COMMIT WORK. . . . .
CONNECT . . . . . . .
CREATE AUDIT . . . . .
CREATE DATABASE . . .
CREATE INDEX . . . . .
CREATE PROCEDURE . .
CREATE PROCEDURE FROM
CREATE ROLE . . . . .
CREATE SCHEMA . . . .
CREATE SYNONYM . . .
CREATE TABLE . . . . .
CREATE TRIGGER . . . .
CREATE VIEW . . . . .
DATABASE. . . . . . .
DEALLOCATE DESCRIPTOR
DECLARE . . . . . . .
DELETE . . . . . . . .
DESCRIBE . . . . . . .
DISCONNECT . . . . .
DROP AUDIT . . . . . .
DROP DATABASE . . . .
DROP INDEX . . . . . .
DROP PROCEDURE . . .
DROP ROLE . . . . . .
DROP SYNONYM . . . .
DROP TABLE . . . . . .
DROP TRIGGER . . . . .
DROP VIEW . . . . . .
EXECUTE . . . . . . .
EXECUTE IMMEDIATE . .
EXECUTE PROCEDURE . .
FETCH . . . . . . . .
FLUSH . . . . . . . .
FREE . . . . . . . . .
GET DESCRIPTOR . . . .
GET DIAGNOSTICS . . .
GRANT . . . . . . . .
GRANT FRAGMENT . . .
INFO . . . . . . . . .
INSERT . . . . . . . .
LOAD . . . . . . . .
LOCK TABLE . . . . . .
OPEN. . . . . . . . .
OUTPUT . . . . . . .
PREPARE . . . . . . .
PUT . . . . . . . . .
iv
Informix Guide to SQL: Syntax
. . . . . . . . . . . . 1-79
. . . . . . . . . . . . 1-81
. . . . . . . . . . . . 1-85
. . . . . . . . . . . . 1-87
. . . . . . . . . . . . 1-89
. . . . . . . . . . . . 1-102
. . . . . . . . . . . . 1-104
. . . . . . . . . . . . 1-109
. . . . . . . . . . . . 1-134
. . . . . . . . . . . . 1-144
. . . . . . . . . . . . 1-145
. . . . . . . . . . . . 1-147
. . . . . . . . . . . . 1-150
. . . . . . . . . . . . 1-154
. . . . . . . . . . . . 1-192
. . . . . . . . . . . . 1-224
. . . . . . . . . . . . 1-229
. . . . . . . . . . . . 1-232
. . . . . . . . . . . . 1-234
. . . . . . . . . . . . 1-252
. . . . . . . . . . . . 1-255
. . . . . . . . . . . . 1-261
. . . . . . . . . . . . 1-265
. . . . . . . . . . . . 1-266
. . . . . . . . . . . . 1-268
. . . . . . . . . . . . 1-270
. . . . . . . . . . . . 1-271
. . . . . . . . . . . . 1-272
. . . . . . . . . . . . 1-274
. . . . . . . . . . . . 1-277
. . . . . . . . . . . . 1-279
. . . . . . . . . . . . 1-281
. . . . . . . . . . . . 1-290
. . . . . . . . . . . . 1-293
. . . . . . . . . . . . 1-296
. . . . . . . . . . . . 1-308
. . . . . . . . . . . . 1-311
. . . . . . . . . . . . 1-314
. . . . . . . . . . . . 1-321
. . . . . . . . . . . . 1-340
. . . . . . . . . . . . 1-356
. . . . . . . . . . . . 1-365
. . . . . . . . . . . . 1-370
. . . . . . . . . . . . 1-380
. . . . . . . . . . . . 1-387
. . . . . . . . . . . . 1-390
. . . . . . . . . . . . 1-400
. . . . . . . . . . . . 1-402
. . . . . . . . . . . . 1-416
RECOVER TABLE . . . . . .
RENAME COLUMN . . . . .
RENAME DATABASE . . . .
RENAME TABLE . . . . . .
REPAIR TABLE . . . . . . .
REVOKE . . . . . . . . .
REVOKE FRAGMENT . . . .
ROLLBACK WORK . . . . .
ROLLFORWARD DATABASE. .
SELECT . . . . . . . . .
SET . . . . . . . . . . .
SET CONNECTION . . . . .
SET DATASKIP . . . . . . .
SET DEBUG FILE TO . . . . .
SET DESCRIPTOR . . . . . .
SET EXPLAIN . . . . . . .
SET ISOLATION . . . . . .
SET LOCK MODE . . . . . .
SET LOG . . . . . . . . .
SET OPTIMIZATION . . . . .
SET PDQPRIORITY . . . . .
SET ROLE . . . . . . . .
SET SESSION AUTHORIZATION
SET TRANSACTION . . . . .
START DATABASE . . . . .
START VIOLATIONS TABLE . .
STOP VIOLATIONS TABLE . .
UNLOAD . . . . . . . . .
UNLOCK TABLE . . . . . .
UPDATE . . . . . . . . .
UPDATE STATISTICS . . . .
WHENEVER. . . . . . . .
Segments . . . . . . . . . .
Condition . . . . . . . . .
Constraint Name . . . . . .
Database Name . . . . . . .
Data Type . . . . . . . . .
DATETIME Field Qualifier . . .
Expression . . . . . . . .
Identifier . . . . . . . . .
Index Name . . . . . . . .
INTERVAL Field Qualifier . . .
Literal DATETIME. . . . . .
Literal INTERVAL . . . . . .
Literal Number . . . . . . .
Procedure Name . . . . . .
Quoted String . . . . . . .
Relational Operator . . . . .
Synonym Name . . . . . .
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1-425
1-428
1-431
1-432
1-435
1-437
1-450
1-455
1-457
1-459
1-501
1-527
1-534
1-537
1-540
1-548
1-556
1-561
1-564
1-566
1-568
1-571
1-573
1-575
1-581
1-584
1-603
1-605
1-610
1-612
1-623
1-632
1-640
1-643
1-658
1-660
1-664
1-669
1-671
1-723
1-741
1-743
1-746
1-749
1-752
1-754
1-757
1-761
1-766
Table of Contents
v
Table Name.
View Name .
Chapter 2
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. 1-768
. 1-772
Informix Guide to SQL: Syntax
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CALL . . . . . .
CONTINUE . . .
DEFINE . . . . .
EXIT . . . . . .
FOR . . . . . .
FOREACH . . . .
IF . . . . . . .
LET . . . . . .
ON EXCEPTION . .
RAISE EXCEPTION .
RETURN . . . .
SYSTEM . . . . .
TRACE . . . . .
WHILE . . . . .
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SPL Statements
Index
vi
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2-4
2-7
2-8
2-16
2-18
2-23
2-27
2-31
2-34
2-39
2-41
2-43
2-46
2-49
Introduction
Introduction
Products Covered in This Manual.
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3
About This Manual . . . . . . . . . . .
Organization of This Manual . . . . . .
Types of Users . . . . . . . . . . .
Software Dependencies . . . . . . . .
Assumptions About Your Database Server
Assumptions About Your Locale . . .
Demonstration Database . . . . . . .
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6
7
8
New Features of This Product .
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11
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16
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23
24
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25
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Conventions . . . . . . . . . . . .
Typographical Conventions . . . . .
Icon Conventions . . . . . . . . .
Comment Icons . . . . . . . .
Product and Platform Icons . . . .
Compliance Icons . . . . . . .
Syntax Conventions . . . . . . . .
Elements That Can Appear on the Path
How to Read a Syntax Diagram . . .
Sample-Code Conventions . . . . . .
Terminology Conventions . . . . . .
Definitions of Terms . . . . . . .
Abbreviations of Product Names . .
.
2
Additional Documentation . . . . . . . . . . . .
Printed Documentation . . . . . . . . . . . .
On-Line Documentation . . . . . . . . . . . .
Error Message Files . . . . . . . . . . . .
Release Notes, Documentation Notes, Machine Notes
Related Reading . . . . . . . . . . . . . .
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26
26
27
28
28
29
Compliance with Industry Standards.
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30
Informix Welcomes Your Comments .
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30
Informix Guide to SQL: Syntax
T
his chapter introduces the Informix Guide to SQL: Syntax manual. Read
this chapter for an overview of the information provided in this manual and
for an understanding of the conventions used throughout this manual.
Products Covered in This Manual
All the information presented in this manual is valid for the following products. Differences in their use of SQL are indicated where appropriate:
■
INFORMIX-ESQL/C, Version 7.2
■
INFORMIX-ESQL/COBOL, Version 7.2
■
INFORMIX-OnLine Dynamic Server, Version 7.2
■
INFORMIX-SE, Version 7.2
Important: This manual does not cover the product called INFORMIX-SQL or any
other Informix application development tool. Each of these tools is covered in its own
manual set. This manual is valid only for the products in the preceding list.
About This Manual
The Informix Guide to SQL: Syntax is intended to be used as a companion
volume to the Informix Guide to SQL: Reference and Informix Guide to SQL:
Tutorial. This manual and the Informix Guide to SQL: Reference are references
that you can use on a daily basis after you finish reading and experimenting
with the Informix Guide to SQL: Tutorial.
Introduction
3
Organization of This Manual
This manual contains all the syntax descriptions for Structured Query
Language (SQL) and Stored Procedure Language (SPL) statements. The
Informix Guide to SQL: Tutorial explains the philosophy and concepts behind
relational databases, and the Informix Guide to SQL: Reference provides
reference information for aspects of SQL other than the language statements.
Organization of This Manual
The Informix Guide to SQL: Syntax includes the following chapters:
4
■
The Introduction explains the purpose and organization of this manual, introduces the demonstration database from which the product
examples in the manual are drawn, lists the new features for
Version 7.2 of Informix database server products that use SQL, and
describes the syntax conventions followed in the manual.
■
Chapter 1, “SQL Statements,” describes SQL statements and segments. The chapter is divided into six sections. The first four sections
provide an introduction to the statements and segments. These sections cover the following subjects: entry of SQL statements, entry of
SQL comments, categories of SQL statements, and categories of ANSI
compliance. The fifth and sixth sections, “Statements” and “Segments,” are the major sections of the chapter.
Informix Guide to SQL: Syntax
❑
“Statements” explains the workings of all the SQL statements
that Informix products support. Detailed syntax diagrams walk
you through every clause of each SQL statement, and syntax
tables explain the input parameters for each clause. Thorough
usage instructions, pertinent examples, and references to related
material complete the description of each SQL statement.
❑
“Segments” explains all the SQL segments. SQL segments are
language elements, such as table names and expressions, that
occur in many SQL statements. Instead of describing each
segment in each statement where it occurs, this manual provides
a comprehensive stand-alone description of each segment.
Whenever a segment occurs within a given syntax diagram, the
diagram points to the stand-alone description of the segment in
this section for further information.
Types of Users
■
Chapter 2, “SPL Statements,” presents all the detailed syntax diagrams and explanations for SPL statements. You can use stored procedures to perform any function you can perform in SQL as well as
to expand what you can accomplish with SQL alone. You write a
stored procedure using SPL and SQL statements. For task-oriented
information about using stored procedures, see the Informix Guide to
SQL: Tutorial.
■
The Index is a combined index for the manuals in the SQL series.
Each page reference in the index ends with a code that identifies the
manual in which the page appears. The same index also appears in
the Informix Guide to SQL: Reference and the Informix Guide to SQL:
Tutorial.
The following items in the SQL manual series are an integral part of the
Informix Guide to SQL: Syntax even though they do not appear physically in
this manual:
■
A description of the stores7 database appears in Appendix A of the
Informix Guide to SQL: Reference. This appendix describes the
structure and contents of the demonstration database that is installed
with the Informix database server products. All the manuals in the
SQL manual series use this database for their examples.
■
Definitions of terms that are used in the SQL manual series appear in
the Glossary of the Informix Guide to SQL: Reference.
SQL messages that the database server issues to reflect errors in the execution
of SQL statements are described in the section on SQL error codes in the
Informix Error Messages manual.
Types of Users
This manual is written for people who use Informix products and SQL on a
regular basis. The primary audience for this manual consists of SQL developers and database administrators. The secondary audience consists of end
users and anyone else who needs to know the syntax of SQL statements.
Introduction
5
Software Dependencies
Software Dependencies
You must have the following Informix software to enter and execute SQL and
SPL statements:
■
An INFORMIX-OnLine Dynamic Server database server or an
INFORMIX-SE database server.
The database server must be installed either on your computer or on
another computer to which your computer is connected over a
network.
■
Either an Informix application development tool, such as
INFORMIX-4GL; an SQL application programming interface (API),
such as INFORMIX-ESQL/C; or the DB-Access database access utility,
which is shipped as part of your database server.
The application development tool, the SQL API, or DB-Access enables
you to compose queries, send them to the database server, and view
the results that the database server returns.
You can use DB-Access to try out many of the SQL statements
described in this manual. See the DB-Access User Manual for a list of
all the SQL statements that you can run from DB-Access.
Assumptions About Your Database Server
This manual assumes that you are using INFORMIX-OnLine Dynamic Server
as your database server. Thus information that is valid only for OnLine is not
called out as such in the text of this manual, unless a particular piece of text
emphasizes a contrast between OnLine and INFORMIX-SE. However, in
syntax diagrams, syntax paths valid only for OnLine are identified by a
product icon as an aid to users.
Features and behavior specific to INFORMIX-SE are noted throughout the text
of this manual. Information valid only for SE is identified by a product icon
in the text, and syntax paths valid only for SE are identified by the same
product icon in syntax diagrams.
6
Informix Guide to SQL: Syntax
Software Dependencies
Assumptions About Your Locale
This manual assumes that you are using the default locale, U.S. 8859-1
English. This locale provides support for the U.S. English language, the ISO
8859-1 code set, and standard U.S. conventions for the formatting of
monetary, numeric, date, and time data. This locale has the following name:
en_us.8859-1
In this name, en indicates the English language, us indicates the United
States territory, and 8859-1 indicates the ISO 8859-1 code set. The ASCII code
set is a subset of the ISO 8859-1 code set.
However, Informix products can support more than one language, culture, or
code set. All culture-specific information is brought together in a single
environment, called a GLS (Global Language Support) locale. If you plan to
use non-English characters in your data or in SQL identifiers, or if you want
to conform to the sorting and collation standards of a non-U.S. English
language or territory, you need to specify the appropriate nondefault locale.
See the Guide to GLS Functionality for instructions on specifying a locale.
If you are using the default U.S. English locale, the Informix Guide to SQL:
Syntax provides all the syntax information that you need for using SQL statements and segments. You do not need to refer to the Guide to GLS Functionality for any additional syntax or considerations.
However, if you are using a nondefault locale, you need to use the Informix
Guide to SQL: Syntax in conjunction with the Guide to GLS Functionality. The
chapter on SQL features in that manual explains the effect of the GLS feature
on SQL statements and segments. That chapter approaches SQL from a
non-U.S. English perspective, so it is a necessary companion to the Informix
Guide to SQL: Syntax if you are using a nondefault locale.
Introduction
7
Demonstration Database
Demonstration Database
The DB-Access utility, which is provided with your Informix database server
products, includes a demonstration database called stores7 that contains
information about a fictitious wholesale sporting-goods distributor. The
sample command files that make up a demonstration application are also
included.
Most examples in this manual are based on the stores7 demonstration
database. The stores7 database is described in detail and its contents are
listed in Appendix A of the Informix Guide to SQL: Reference.
The script that you use to install the demonstration database is called
dbaccessdemo7 and is located in the $INFORMIXDIR/bin directory. The
database name that you supply is the name given to the demonstration
database. If you do not supply a database name, the name defaults to stores7.
Use the following rules for naming your database:
■
Names can have a maximum of 18 characters for INFORMIX-OnLine
Dynamic Server databases and a maximum of 10 characters for
INFORMIX-SE databases.
■
The first character of a name must be a letter or an underscore (_).
■
You can use letters, characters, and underscores (_) for the rest of the
name.
■
DB-Access makes no distinction between uppercase and lowercase
letters.
■
The database name must be unique.
When you run dbaccessdemo7, as the creator of the database, you are the
owner and Database Administrator (DBA) of that database.
If you install your Informix database server according to the installation
instructions, the files that constitute the demonstration database are
protected so that you cannot make any changes to the original database.
8
Informix Guide to SQL: Syntax
Demonstration Database
You can run the dbaccessdemo7 script again whenever you want to work
with a fresh demonstration database. The script prompts you when the
creation of the database is complete and asks if you would like to copy the
sample command files to the current directory. Enter N if you have made
changes to the sample files and do not want them replaced with the original
versions. Enter Y if you want to copy over the sample command files.
To create and populate the stores7 demonstration database
1.
Set the INFORMIXDIR environment variable so that it contains the
name of the directory in which your Informix products are installed.
2.
Set INFORMIXSERVER to the name of the default database server.
The name of the default database server must exist in the
$INFORMIXDIR/etc/sqlhosts file. (For a full description of
environment variables, see Chapter 4 of the Informix Guide to SQL:
Reference.) For information about sqlhosts, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide or the
INFORMIX-SE Administrator’s Guide.
3.
Create a new directory for the SQL command files. Create the
directory by entering the following command:
mkdir dirname
4.
Make the new directory the current directory by entering the
following command:
cd dirname
Introduction
9
Demonstration Database
5.
Create the demonstration database and copy over the sample
command files by entering the dbaccessdemo7 command.
To create the database without logging, enter the following
command:
dbaccessdemo7 dbname
To create the demonstration database with logging, enter the
following command:
dbaccessdemo7 -log dbname
If you are using INFORMIX-OnLine Dynamic Server, by default the
data for the database is put into the root dbspace. If you wish, you
can specify a dbspace for the demonstration database.
To create a demonstration database in a particular dbspace, enter the
following command:
dbaccessdemo7 dbname -dbspace dbspacename
You can specify all of the options in one command, as shown in the
following command:
dbaccessdemo7 -log dbname -dbspace dbspacename
If you are using INFORMIX-SE, a subdirectory called dbname.dbs is
created in your current directory and the database files associated
with stores7 are placed there. You will see both data (.dat) and index
(.idx) files in the dbname.dbs directory. (If you specify a dbspace
name, it is ignored.)
To use the database and the command files that have been copied to
your directory, you must have UNIX read and execute permissions
for each directory in the pathname of the directory from which you
ran the dbaccessdemo7 script. Check with your system administrator for more information about operating-system file and
directory permissions. UNIX permissions are discussed in the
INFORMIX-OnLine Dynamic Server Administrator’s Guide and the
INFORMIX-SE Administrator’s Guide.
6.
To give someone else the permissions to access the command files in
your directory, use the UNIX chmod command.
7.
To give someone else access to the database that you have created,
grant them the appropriate privileges using the GRANT statement.
To revoke privileges, use the REVOKE statement. The GRANT and
REVOKE statements are described in Chapter 1 of this manual.
10
Informix Guide to SQL: Syntax
New Features of This Product
New Features of This Product
The Introduction to each Version 7.2 product manual contains a list of new
features for that product. The Introduction to each manual in the Version 7.2
Informix Guide to SQL series contains a list of new SQL features.
A comprehensive list of all of the new features for Version 7.2 Informix
products is in the release-notes file called SERVERS_7.2.
This section highlights the major new features implemented in Version 7.2 of
Informix products that use SQL:
■
Addition of Global Language Support (GLS)
The GLS feature allows you to work in any supported language and
to conform to the customs of a specific territory by setting certain
environment variables. In support of GLS, CHAR and VARCHAR,
columns of the system catalog tables are created as NCHAR and
NVARCHAR columns in this release. In addition, hidden rows have
been added to the systables system catalog table. See the discussion
of GLS in Chapter 1 of the Informix Guide to SQL: Reference.
■
ANSI flagger
The ANSI flagger that Informix products use has been modified to
eliminate the flagging of certain SQL items as Informix extensions.
These items include the AS keyword in the SELECT clause of the
SELECT statement and delimited identifiers in the Identifier segment.
■
Bidirectional indexes
The database server can now traverse an index in either ascending or
descending order. So you no longer need to create both an ascending
index and a descending index for a column when you use this
column in both SELECT...ORDER BY column name ASC statements and
SELECT...ORDER BY column name DESC statements. You only need to
create a single ascending or descending index for these queries. See
the CREATE INDEX and SELECT statements.
Introduction
11
New Features of This Product
■
Column matches in conditions
When you specify a LIKE or MATCHES condition in the SELECT
statement or other statements, you can specify a column name on
both sides of the LIKE or MATCHES keyword. The database server
retrieves a row when the values of the specified columns match. See
the Condition segment and the SELECT statement.
■
Column substrings in queries
You can specify column subscripts for the column named in a
SELECT...ORDER BY statement. The database server sorts the query
results by the value of the column substring rather than the value of
the entire column.
■
Column updates after a fetch
When you use the FOR UPDATE clause of the SELECT statement, you
can use the OF column name option of this clause to limit the columns
that can be updated after a fetch.
■
Connectivity information
You can use the INFORMIXSQLHOSTS environment variable to
specify the pathname of the file where the client or the database
server looks for connectivity information.
■
COUNT function
The ALL column name option of the COUNT function returns the total
number of non-null values in the specified column or expression. See
the Expression segment.
■
Data distributions
You can suppress the construction of index information in the
MEDIUM and HIGH modes of the UPDATE STATISTICS statement.
When you use the new DISTRIBUTIONS ONLY option of this
statement, the database server gathers only distributions information and table information.
■
Database renaming
You can rename local databases. See the new RENAME DATABASE
statement.
■
DBINFO function
You can use the 'sessionid' option of the DBINFO function to return
the session ID of your current session. See the Expression segment.
12
Informix Guide to SQL: Syntax
New Features of This Product
■
Decimal digits in client applications
Informix client applications (including the DB-Access utility or any
ESQL program that you write) by default display 16 decimal digits of
data types FLOAT, SMALLFLOAT, and DECIMAL. The actual digits
that are displayed can vary according to the size of the character
buffer. The new DBFLTMASK environment variable allows you to
override the default of 16 decimal digits in the display.
■
Default privileges on tables
You can use the new NODEFDAC environment variable to prevent
default table privileges from being granted to PUBLIC when a new
table is created in a database that is not ANSI compliant.
■
Fragment authorization
You can grant and revoke privileges on individual fragments of
tables. See the new GRANT FRAGMENT and REVOKE FRAGMENT
statements and the new sysfragauth system catalog table.
■
High-Performance Loader (HPL) configuration
You can use the new DBONPLOAD and PLCONFIG environment
variables to specify the names of files and databases to be used by
HPL.
■
In-place alter algorithm
INFORMIX-OnLine Dynamic Server uses a new in-place alter
algorithm for altering tables when you add a column to the end of
the table. See the ALTER TABLE statement.
■
Next century in year values
You can use the next century to expand two-digit year values. See the
new DBCENTURY environment variable, the Literal DATETIME
segment, the DATE data type, and the DATETIME data type.
■
Not null constraints
You can now create not null constraints with the CREATE TABLE and
ALTER TABLE statements. The database server records not null
constraints in the sysconstraints and syscoldepend system catalog
tables.
Introduction
13
New Features of This Product
■
Object modes
You can specify the object mode of database objects with the new SET
statement. This statement permits you to set the object mode of
constraints, indexes, and triggers or the transaction mode of
constraints. See the SET statement, the new sysobjstate system
catalog table, and the new syntax for object modes in ALTER TABLE,
CREATE INDEX, CREATE TABLE, and CREATE TRIGGER.
■
Optical StageBlob area
You can use the new INFORMIXOPCACHE environment variable to
specify the size of the memory cache for the Optical StageBlob area
of the client application.
■
RANGE, STDEV, and VARIANCE functions
You can use the new aggregate functions RANGE, STDEV, and
VARIANCE. See the new syntax for Aggregate Expressions in the
Expression segment.
■
Roles
You can create, drop, and enable roles. You can grant roles to
individual users and to other roles, and you can grant privileges to
roles. You can revoke a role from individual users and from another
role, and you can revoke privileges from a role. See the new CREATE
ROLE, DROP ROLE, and SET ROLE statements and the new
sysroleauth system catalog table. Also see the new syntax for roles in
the GRANT and REVOKE statements and the new information in the
sysusers system catalog table.
■
Separation of administrative tasks
The security feature of role separation allows you to separate administrative tasks performed by different groups that are running and
auditing OnLine. The INF_ROLE_SEP environment variable allows
you to implement role separation during installation of OnLine.
■
Session authorization
You can change the user name under which database operations are
performed in the current session and thus assume the privileges of
the specified user during the session. See the new SET SESSION
AUTHORIZATION statement.
14
Informix Guide to SQL: Syntax
New Features of This Product
■
Table access after loads
The FOR READ ONLY clause of the SELECT statement allows you to
access data in the tables of an ANSI-mode database after you have
loaded the data with the High-Performance Loader but before you
have performed a level-0 backup of the data. After you have
performed the level-0 backup, you no longer need to use the FOR
READ ONLY clause. See the SELECT and DECLARE statements.
■
Thread-safe applications
You can use the new THREADLIB environment variable to compile
thread-safe ESQL/C applications. In a thread-safe ESQL/C application, you can use the DORMANT option of the SET CONNECTION
statement to make an active connection dormant.
■
Tutorials
Tutorial information on new features has been added to the Informix
Guide to SQL: Tutorial. The new tutorials cover Global Language
Support (GLS), thread-safe applications, object modes, violation
detection, fragment authorization, and roles.
■
Utilities
The dbexport, dbimport, dbload, and dbschema utilities have been
moved from the Informix Guide to SQL: Reference to the Informix
Migration Guide.
■
Violation detection
You can create special tables called violations and diagnostics tables
to detect integrity violations. See the new START VIOLATIONS TABLE
and STOP VIOLATIONS TABLE statements and the new sysviolations
system catalog table.
■
XPG4 compliance
SQL statements and data structures have been modified to provide
enhanced compliance with the X/Open Portability Guide 4 (XPG4) specification for SQL. The sqlwarn array within the SQL Communications
Area (SQLCA) has been modified. A new SQLSTATE code (01007) has
been added. The behavior of the ALL keyword in the GRANT
statement and the behavior of the ALL and RESTRICT keywords in
the REVOKE statement has changed.
Introduction
15
Conventions
See this manual for SQL statements and segments. See the Informix Guide to
SQL: Reference for data types, system catalog tables, and environment
variables. See the Informix Guide to SQL: Tutorial for tutorial information.
Conventions
This section describes the conventions that are used in this manual. By
becoming familiar with these conventions, you will find it easier to gather
information from this and other volumes in the documentation set.
The following conventions are covered:
■
Typographical conventions
■
Icon conventions
■
Syntax conventions
■
Sample-code conventions
■
Terminology conventions
Typographical Conventions
This manual uses a standard set of conventions to emphasize words, present
examples, describe statement syntax, and so forth. The following
typographical conventions are used throughout this manual.
Convention
Meaning
italics
Within text, emphasized words are printed in italics. Within
syntax diagrams, values that you are to specify are printed in
italics.
boldface
Identifiers (names of classes, objects, constants, events,
functions, program variables, forms, labels, and reports),
environment variables, database names, table names, column
names, menu items, command names, and other similar terms
are printed in boldface.
(1 of 2)
16
Informix Guide to SQL: Syntax
Icon Conventions
monospace
Information that the product displays and information that you
enter are printed in a monospace typeface.
KEYWORD
All keywords appear in uppercase letters.
♦
This symbol indicates the end of product- or platform-specific
information.
(2 of 2)
Tip: When you are instructed to “enter” characters or to “execute” a command,
immediately press RETURN after the entry. When you are instructed to “type” the
text or to “press” other keys, no RETURN is required.
Icon Conventions
Throughout the documentation, you will find text that is identified by several
different types of icons. This section describes these icons.
Comment Icons
Comment icons identify three types of information, as described in the
following table. This information is always displayed in italics.
Introduction
17
Icon Conventions
Product and Platform Icons
Product and platform icons identify paragraphs that describe productspecific or platform-specific information. The following table describes the
product and platform icons that are used in this manual.
Icon
Description
SE
Identifies information that is valid only for INFORMIX-SE.
D/B
Identifies information that is valid only for DB-Access.
ESQL
Identifies information that is valid only for SQL statements
in INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL.
E/C
Identifies information that is valid only for
INFORMIX-ESQL/C.
E/CO
Identifies information that is valid only for
INFORMIX-ESQL/COBOL.
SPL
Identifies information that is valid only if you are using
Informix Stored Procedure Language ( ).
OP
Identifies information that is valid only for
INFORMIX-OnLine/Optical.
These icons can apply to a row in a table, one or more paragraphs, or an entire
section. A ♦ symbol indicates the end of the product- or platform-specific
information.
18
Informix Guide to SQL: Syntax
Syntax Conventions
Compliance Icons
Compliance icons indicate paragraphs that provide guidelines for complying
with a standard.
Icon
Description
ANSI
Identifies information that is valid only if your database is
ANSI-compliant.
GLS
Identifies information that is valid only if your database or
application uses a nondefault GLS locale.
X/O
Indicates that the functionality described in the text
conforms to X/Open specifications for dynamic SQL. This
functionality is available when you compile your SQL API
with the -xopen flag.
These icons can apply to a row in a table, one or more paragraphs, or an entire
section. A ♦ symbol indicates the end of the compliance information.
Syntax Conventions
This section describes conventions for syntax diagrams. Each diagram
displays the sequences of required and optional keywords, terms, and
symbols that are valid in a given statement, command line, or other
specification, as in the following diagram of the SET EXPLAIN statement.
+
SET EXPLAIN
ON
OFF
Each syntax diagram begins at the upper left corner and ends at the upper
right corner with a vertical terminator. Between these points, any path that
does not stop or reverse direction describes a possible form of the statement.
(For a few diagrams, notes in the text identify path segments that are
mutually exclusive.)
Introduction
19
Syntax Conventions
Syntax elements in a path represent terms, keywords, symbols, and segments
that can appear in your statement. Except for separators in loops, which the
path approaches counterclockwise from the right, the path always
approaches elements from the left and continues to the right. Unless
otherwise noted, at least one blank character separates syntax elements.
Elements That Can Appear on the Path
You might encounter one or more of the following elements on a path.
Element
Description
KEYWORD
A word in UPPERCASE characters is a keyword. You
must spell the word exactly as shown; however, you
can use either uppercase or lowercase characters.
(.,;@+*-/)
Punctuation and other non-alphanumeric characters
are literal symbols that you must enter exactly as
shown.
' '
Single quotes are literal symbols that you must enter
as shown.
variable
A word in italics represents a value that you must
supply. A table immediately following the diagram
explains the value.
ADD
Clause
p. 1-14
ADD Clause
OL
A term shown in a rectangle represents a subdiagram
on the same page (if no page number is supplied) or a
specified page, as if the subdiagram were spliced into
the diagram at this point. The same subdiagram can be
represented by rectangles of different shapes, as in
these symbols for the ADD Clause subdiagram.
An icon is a warning that this path is valid only for
some products, or only under certain conditions.
Characters on the icons indicate what products or
conditions support the path.
These icons might appear in a syntax diagram:
OL
This path is valid only for
INFORMIX-OnLine Dynamic Server.
(1 of 3)
20
Informix Guide to SQL: Syntax
Syntax Conventions
Element
Description
SE
This path is valid only for INFORMIX-SE.
D/B
This path is valid only for DB-Access.
ESQL
ALL
This path is valid only for SQL statements
in INFORMIX-ESQL/C and
INFORMIX-ESQL/COBOL.
E/C
This path is valid only for
INFORMIX-ESQL/C.
E/CO
This path is valid only for
INFORMIX-ESQL/COBOL.
SPL
This path is valid only if you are using
Informix Stored Procedure Language
(SPL).
OP
This path is valid only for
INFORMIX-OnLine/Optical.
+
This path is an Informix extension to
ANSI SQL-92 entry-level standard SQL. If
you initiate Informix extension checking
and include this syntax branch, you
receive a warning. If you have set the
DBANSIWARN environment variable at
compile time, or have used the -ansi
compile flag, you receive warnings at
compile time. If you have DBANSIWARN
set at runtime, or if you compiled with
the -ansi flag, warning flags are set in the
sqlwarn structure.
GLS
This path is valid only if your database or
application uses a nondefault GLS locale.
A shaded option is the default. If you do not specify
any of the available options, this option is in effect by
default.
Syntax that is enclosed between a pair of arrows is
a subdiagram.
(2 of 3)
Introduction
21
Syntax Conventions
Element
Description
The vertical line is a terminator. This symbol only
appears at the right, indicating that the syntax
diagram is complete.
IS
NULL
NOT
NOT FOUND
ERROR
A branch below the main path indicates an optional
path. (Any term on the main path is required, unless
a branch can circumvent it.)
A set of multiple branches indicates that a choice
among more than two different paths is available.
WARNING
,
variable
A loop indicates a path that you can repeat.
Punctuation along the top of the loop indicates the
separator symbol for list items, as in this example. If no
symbol appears, a blank space is the separator,
statement
,
3 size
A gate ( 3 ) on a path indicates that you can only use
that path the indicated number of times, even if it is
part of a larger loop. Here you can specify size no more
than three times within this statement segment.
(3 of 3)
22
Informix Guide to SQL: Syntax
Syntax Conventions
How to Read a Syntax Diagram
Figure 1 shows a syntax diagram that uses most of the path elements that are
listed in the previous table.
Figure 1
Elements of a Syntax Diagram
Main diagram
CREATE DATABASE database name
OL
IN dbspace
Subdiagram
OL
OL Log Clause
SE
SE Log Clause
OL Log Clause
WITH
LOG
BUFFERED
LOG MODE ANSI
SE Log Clause
WITH LOG IN 'pathname'
MODE ANSI
To use this diagram to construct a statement, start at the top left with the
keywords CREATE DATABASE. Then follow the diagram to the right,
proceeding through the options that you want.
Introduction
23
Sample-Code Conventions
To read the example syntax diagram
1.
You must type the words CREATE DATABASE.
2.
You must supply a database name.
3.
You can stop, taking the direct route to the terminator, or you can
take one or more of the optional paths.
4.
If desired, you can designate a dbspace by typing the word IN and a
dbspace name.
5.
If desired, you can specify logging. Here, you are constrained by the
database server with which you are working.
6.
❑
If you are using INFORMIX-OnLine Dynamic Server, go to the
subdiagram named OL Log Clause. Follow the subdiagram by
typing the keyword WITH, then choosing and typing either LOG,
BUFFERED LOG, or LOG MODE ANSI. Then, follow the arrow
back to the main diagram.
❑
If you are using INFORMIX-SE, go to the subdiagram named SE
Log Clause. Follow the subdiagram by typing the keywords
WITH LOG IN, typing a quote, supplying a pathname, and closing the quotes. You can then choose the MODE ANSI option
below the line or continue to follow the line across.
Once you are back at the main diagram, you come to the terminator.
Your CREATE DATABASE statement is complete.
Sample-Code Conventions
Examples of SQL code occur throughout this manual. Except where noted,
the code is not specific to any single Informix application development tool.
If only SQL statements are listed in the example, they are not delimited by
semicolons. To use this SQL code for a specific product, you must apply the
syntax rules for that product. For example, if you are using the
Query-language option of DB-Access, you must delimit multiple statements
with semicolons. If you are using an SQL API, you must use EXEC SQL and a
semicolon (or other appropriate delimiters) at the start and end of each
statement, respectively.
24
Informix Guide to SQL: Syntax
Terminology Conventions
For instance, you might see the code in the following example:
CONNECT TO stores7
.
.
.
DELETE FROM customer
WHERE customer_num = 121
.
.
.
COMMIT WORK
DISCONNECT CURRENT
Dots in the example indicate that more code would be added in a full
application, but it is not necessary to show it to describe the concept being
discussed.
For detailed directions on using SQL statements for a particular application
development tool or SQL API, see the manual for your product.
Terminology Conventions
This manual uses a standard set of conventions for terms and abbreviations.
Definitions of Terms
For definitions of terms used in this manual and in the other manuals of the
SQL series, see the Glossary in the Informix Guide to SQL: Reference.
Abbreviations of Product Names
The following abbreviations for product names and features appear in this
manual.
Abbreviation
Complete Name
GLS
Global Language Support
OnLine
INFORMIX-OnLine Dynamic Server
SE
INFORMIX-SE
SQL
Structured Query Language
Introduction
25
Additional Documentation
Additional Documentation
This section describes the following pieces of the documentation set:
■
Printed documentation
■
On-line documentation
■
Related reading
Printed Documentation
In addition to this manual, the following printed manuals are included in the
SQL manual series:
26
■
A companion volume to this manual, the Informix Guide to SQL:
Reference, provides reference information on the types of Informix
databases you can create, the data types supported in Informix
products, system catalog tables associated with the database, and
environment variables you can set to use your Informix products
properly. This manual also provides a detailed description of the
stores7 demonstration database and contains a glossary.
■
An additional companion volume to this manual, the Informix Guide
to SQL: Tutorialprovides a tutorial on SQL as it is implemented by
Informix products. It describes the fundamental ideas and terminology that are used when planning, using, and implementing a
relational database.
■
The SQL Quick Syntax Guide contains syntax diagrams for all statements and segments described in this manual.
Informix Guide to SQL: Syntax
On-Line Documentation
The following related Informix documents complement the information in
this manual set:
■
Getting Started with Informix Database Server Products provides an
orientation to the Informix client/server environment and describes
the manuals for Informix products. If you are a new user of Informix
products, it is helpful to read this manual before you read any of the
manuals in the SQL manual series.
■
The Guide to GLS Functionality explains the impact of the GLS feature
on Informix products. This manual includes a chapter on SQL
features and a chapter on GLS environment variables.
■
You, or whoever installs your Informix products, should refer to the
UNIX Products Installation guide for your particular release to ensure
that your Informix product is properly set up before you begin to
work with it. A matrix that depicts possible client/server configurations is included in the UNIX Products Installation guide.
■
Depending on the database server you are using, you or your system
administrator need either theINFORMIX-SE Administrator’s Guide or
the INFORMIX-OnLine Dynamic Server Administrator’s Guide. The
DB-Access User Manual describes how to invoke the DB-Access utility
to access, modify, and retrieve information from Informix database
servers.
■
When errors occur, you can look them up by number and learn their
cause and solution in the Informix Error Messages manual. If you
prefer, you can look up the error messages in the on-line message file
described in the section “Error Message Files” later in this Introduction and in the Introduction to the Informix Error Messages
manual.
On-Line Documentation
The following online files supplement this document:
■
On-line error messages
■
Release notes, documentation notes, and machine notes
Introduction
27
On-Line Documentation
Error Message Files
Informix software products provide ASCII files that contain all of the
Informix error messages and their corrective actions. To read the error
messages in the ASCII file, Informix provides scripts that let you display error
messages on the screen (finderr) or print formatted error messages (rofferr).
See the Introduction to the Informix Error Messages manual for a detailed
description of these scripts.
The optional Informix Messages and Corrections product provides
PostScript files that contain the error messages and their corrective actions. If
you have installed this product, you can print the PostScript files on a
PostScript printer. The PostScript error messages are distributed in a number
of files of the format errmsg1.ps, errmsg2.ps, and so on. These files are
located in the $INFORMIXDIR/msg directory.
Release Notes, Documentation Notes, Machine Notes
In addition to the Informix set of manuals, the following on-line files, located
in the $INFORMIXDIR/release/en_us/0333 directory, supplement the information in this manual.
On-Line File
Purpose
Documentation
Notes
Describes features that are not covered in the manual or that
have been modified since publication. The file that contains
the documentation notes for this product is called
SQLSDOC_7.2.
28
Release Notes
Describes feature differences from earlier versions of Informix
products and how these differences might affect current
products. The file that contains the release notes for
Version 7..2 of Informix database server products is called
SERVERS_7.2.
Machine Notes
Describes any special actions required to configure and use
Informix products on your computer. Machine notes are
named for the product described. For example, the machine
notes file for INFORMIX-OnLine Dynamic Server is
ONLINE_7.2.
Informix Guide to SQL: Syntax
Related Reading
Please examine these files because they contain vital information about
application and performance issues.
Related Reading
For additional technical information on database management, consult the
following books. The first book is an introductory text for readers who are
new to database management, while the second book is a more complex
technical work for SQL programmers and database administrators:
■
Database: A Primer by C. J. Date (Addison-Wesley Publishing, 1983)
■
An Introduction to Database Systems by C. J. Date (Addison-Wesley
Publishing, 1994).
To learn more about the SQL language, consider the following books:
■
A Guide to the SQL Standard by C. J. Date with H. Darwen (AddisonWesley Publishing, 1993)
■
Understanding the New SQL: A Complete Guide by J. Melton and A.
Simon (Morgan Kaufmann Publishers, 1993)
■
Using SQL by J. Groff and P. Weinberg (Osborne McGraw-Hill, 1990)
This manual assumes that you are familiar with your computer operating
system. If you have limited UNIX system experience, consult your operating
system manual or a good introductory text before you read this manual. The
following texts provide a good introduction to UNIX systems:
■
Introducing the UNIX System by H. McGilton and R. Morgan
(McGraw-Hill Book Company, 1983)
■
Learning the UNIX Operating System by G. Todino, J. Strang, and
J. Peek (O’Reilly & Associates, 1993)
■
A Practical Guide to the UNIX System by M. Sobell
(Benjamin/Cummings Publishing, 1989)
■
UNIX for People by P. Birns, P. Brown, and J. Muster (Prentice-Hall,
1985)
■
UNIX System V: A Practical Guide by M. Sobell (Benjamin/Cummings
Publishing, 1995)
Introduction
29
Compliance with Industry Standards
Compliance with Industry Standards
The American National Standards Institute (ANSI) has established a set of
industry standards for SQL. Informix SQL-based products are fully compliant
with SQL-92 Entry Level (published as ANSI X3.135-1992), which is identical
to ISO 9075:1992 on INFORMIX-OnLine Dynamic Server. In addition, many
features of OnLine comply with the SQL-92 Intermediate and Full Level and
X/Open CAE (common applications environment) standards.
Informix SQL-based products are compliant with ANSI SQL-92 Entry Level
(published as ANSI X3.135-1992) on INFORMIX-SE with the following
exceptions:
■
Effective checking of constraints
■
Serializable transactions
Informix Welcomes Your Comments
Please let us know what you like or dislike about our manuals. To help us
with future versions of our manuals, please tell us about any corrections or
clarifications that you would find useful. Write to us at the following address:
Informix Software, Inc.
SCT Technical Publications Department
4100 Bohannon Drive
Menlo Park, CA 94025
If you prefer to send electronic mail, our address is:
doc@informix.com
Or send a facsimile to the Informix Technical Publications Department at:
415-926-6571
30
Informix Guide to SQL: Syntax
Informix Welcomes Your Comments
Please include the following information:
■
The name and version of the manual that you are using
■
Any comments that you have about the manual
■
Your name, address, and phone number
We appreciate your feedback.
Introduction
31
Chapter
SQL Statements
1
How to Enter SQL Statements .
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1-6
How to Enter SQL Comments .
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1-9
Categories of SQL Statements .
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1-12
ANSI Compliance and Extensions
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1-16
Statements . . . . . . . . .
ALLOCATE DESCRIPTOR . .
ALTER FRAGMENT . . . .
ALTER INDEX . . . . . .
ALTER TABLE . . . . . .
BEGIN WORK . . . . . .
CHECK TABLE. . . . . .
CLOSE. . . . . . . . .
CLOSE DATABASE . . . .
COMMIT WORK . . . . .
CONNECT . . . . . . .
CREATE AUDIT . . . . .
CREATE DATABASE. . . .
CREATE INDEX . . . . .
CREATE PROCEDURE . . .
CREATE PROCEDURE FROM
CREATE ROLE . . . . . .
CREATE SCHEMA . . . .
CREATE SYNONYM . . . .
CREATE TABLE . . . . .
CREATE TRIGGER . . . .
CREATE VIEW . . . . . .
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1-18
1-19
1-22
1-43
1-46
1-77
1-79
1-81
1-85
1-87
1-89
1-102
1-104
1-109
1-134
1-144
1-145
1-147
1-150
1-154
1-192
1-224
DATABASE . . . . . . .
DEALLOCATE DESCRIPTOR .
DECLARE . . . . . . .
DELETE . . . . . . . .
DESCRIBE . . . . . . .
DISCONNECT . . . . . .
DROP AUDIT . . . . . .
DROP DATABASE. . . . .
DROP INDEX . . . . . .
DROP PROCEDURE . . . .
DROP ROLE . . . . . . .
DROP SYNONYM . . . . .
DROP TABLE . . . . . .
DROP TRIGGER . . . . .
DROP VIEW . . . . . . .
EXECUTE . . . . . . . .
EXECUTE IMMEDIATE . . .
EXECUTE PROCEDURE . .
FETCH . . . . . . . . .
FLUSH . . . . . . . . .
FREE . . . . . . . . .
GET DESCRIPTOR . . . .
GET DIAGNOSTICS . . . .
GRANT . . . . . . . .
GRANT FRAGMENT. . . .
INFO . . . . . . . . .
INSERT . . . . . . . .
LOAD . . . . . . . . .
LOCK TABLE . . . . . .
OPEN . . . . . . . . .
OUTPUT . . . . . . . .
PREPARE . . . . . . . .
PUT . . . . . . . . . .
RECOVER TABLE . . . . .
Informix Guide to SQL: Syntax
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1-229
1-232
1-234
1-252
1-255
1-261
1-265
1-266
1-268
1-270
1-271
1-272
1-274
1-277
1-279
1-281
1-290
1-293
1-296
1-308
1-311
1-314
1-321
1-340
1-356
1-365
1-370
1-380
1-387
1-390
1-400
1-402
1-416
1-425
RENAME COLUMN . . . . .
RENAME DATABASE . . . . .
RENAME TABLE. . . . . . .
REPAIR TABLE . . . . . . .
REVOKE . . . . . . . . .
REVOKE FRAGMENT . . . . .
ROLLBACK WORK . . . . . .
ROLLFORWARD DATABASE . .
SELECT . . . . . . . . . .
SET . . . . . . . . . . .
SET CONNECTION. . . . . .
SET DATASKIP . . . . . . .
SET DEBUG FILE TO . . . . .
SET DESCRIPTOR . . . . . .
SET EXPLAIN . . . . . . . .
SET ISOLATION . . . . . . .
SET LOCK MODE . . . . . .
SET LOG . . . . . . . . .
SET OPTIMIZATION . . . . .
SET PDQPRIORITY . . . . . .
SET ROLE . . . . . . . . .
SET SESSION AUTHORIZATION .
SET TRANSACTION . . . . .
START DATABASE . . . . . .
START VIOLATIONS TABLE . .
STOP VIOLATIONS TABLE . . .
UNLOAD . . . . . . . . .
UNLOCK TABLE. . . . . . .
UPDATE. . . . . . . . . .
UPDATE STATISTICS . . . . .
WHENEVER . . . . . . . .
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. 1-428
. 1-431
. 1-432
. 1-435
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. 1-450
. 1-455
. 1-457
. 1-459
. 1-501
. 1-527
. 1-534
. 1-537
. 1-540
. 1-548
. 1-556
. 1-561
. 1-564
. 1-566
. 1-568
. 1-571
. 1-573
. 1-575
. 1-581
. 1-584
. 1-603
. 1-605
. 1-610
. 1-612
. 1-623
. 1-632
SQL Statements
Segments . . . . . . .
Condition . . . . . .
Constraint Name . . .
Database Name . . . .
Data Type . . . . . .
DATETIME Field Qualifier
Expression . . . . .
Identifier . . . . . .
Index Name . . . . .
INTERVAL Field Qualifier
Literal DATETIME . . .
Literal INTERVAL . . .
Literal Number . . . .
Procedure Name . . .
Quoted String . . . .
Relational Operator . .
Synonym Name. . . .
Table Name . . . . .
View Name . . . . .
Informix Guide to SQL: Syntax
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1-640
1-643
1-658
1-660
1-664
1-669
1-671
1-723
1-741
1-743
1-746
1-749
1-752
1-754
1-757
1-761
1-766
1-768
1-772
T
his chapter provides comprehensive reference information about SQL
statements and the SQL segments that recur in SQL statements. It is organized
into the following sections:
■
“How to Enter SQL Statements” shows how to use the information
in the statement descriptions to enter SQL statements correctly.
■
“How to Enter SQL Comments” shows how to enter comments for
your SQL statements in DB-Access command files, ESQL programs,
and stored procedures.
■
“Categories of SQL Statements” divides SQL statements into several
functional categories and lists the statements within each category.
Some examples of these categories are data definition statements,
data manipulation statements, and data integrity statements.
■
“ANSI Compliance and Extensions” explains how the SQL statements in this manual comply with the ANSI SQL standard. This
section provides a list of ANSI-compliant statements, a list of ANSIcompliant statements with Informix extensions, and a list of statements that are Informix extensions to the ANSI standard.
■
“Statements” gives comprehensive descriptions of SQL statements.
The statements are listed in alphabetical order.
■
“Segments” gives comprehensive descriptions of SQL segments. The
segments are listed in alphabetical order. SQL segments are language
elements, such as table names and expressions, that occur in many
SQL statements. Instead of describing each segment in each
statement where it occurs, this chapter provides a comprehensive
stand-alone description of each segment. Whenever a segment
occurs within the syntax diagram for an SQL statement, the diagram
points to the stand-alone description of the segment for further
information.
SQL Statements 1-5
How to Enter SQL Statements
The following table summarizes the sections of this chapter.
Section
Starting Page
Scope
“How to Enter
SQL Statements”
1-6
This section shows how to use the
statement descriptions to enter SQL
statements correctly.
“How to Enter
SQL Comments”
1-9
This section shows how to enter
comments for SQL statements.
“Categories of SQL
Statements”
1-12
This section lists SQL statements by
functional category.
“ANSI
Compliance and
Extensions”
1-16
This section lists SQL statements by
degree of ANSI compliance.
“Statements”
1-18
This section gives reference descriptions
of all SQL statements.
“Segments”
1-640
This section gives reference descriptions
of all SQL segments.
How to Enter SQL Statements
The purpose of the statement descriptions in this chapter is to help you to
enter SQL statements successfully and to understand the behavior of the
statements. Each statement description includes the following information:
1-6
■
A brief introduction that explains the purpose of the statement
■
A syntax diagram that shows how to enter the statement correctly
■
A syntax table that explains each input parameter in the syntax
diagram
■
Rules of usage, including examples that illustrate these rules
Informix Guide to SQL: Syntax
How to Enter SQL Statements
If a statement consists of multiple clauses, the statement description provides
the same set of information for each clause.
Each statement description concludes with references to related information
in this manual and other manuals.
The major aids for entering SQL statements successfully include:
■
the combination of the syntax diagram and syntax table.
■
the examples of syntax that appear in the rules of usage.
■
the references to related information.
Using Syntax Diagrams and Syntax Tables
Before you try to use the syntax diagrams in this chapter, it is helpful to read
the “Syntax Conventions” on page 19 of the Introduction. This section is the
key to understanding the syntax diagrams in the statement descriptions.
The “Syntax Conventions” section explains the elements that can appear in a
syntax diagram and the paths that connect the elements to each other. This
section also includes a sample syntax diagram that illustrates the major
elements of all syntax diagrams. The narrative that follows the sample
diagram shows how to read the diagram in order to enter the statement
successfully.
When a syntax diagram within a statement description includes input
parameters, the syntax diagram is followed by a syntax table that shows how
to enter the parameters without generating errors. Each syntax table includes
the following columns:
■
The Elements column lists the name of each parameter as it appears
in the syntax diagram.
■
The Purpose column briefly states the purpose of the parameter. If
the parameter has a default value, it is listed in this column.
■
The Restrictions column summarizes the restrictions on the
parameter, such as acceptable ranges of values.
■
The Syntax column points to the SQL segment that gives the detailed
syntax for the parameter.
SQL Statements 1-7
How to Enter SQL Statements
Using Examples
To understand the main syntax diagram and subdiagrams for a statement,
study the examples of syntax that appear in the rules of usage for each
statement. These examples have two purposes:
■
To show how to accomplish particular tasks with the statement or its
clauses
■
To show how to use the syntax of the statement or its clauses in a
concrete way
Tip: An efficient way to understand a syntax diagram is to find an example of the
syntax and compare it with the keywords and parameters in the syntax diagram. By
mapping the concrete elements of the example to the abstract elements of the syntax
diagram, you can understand the syntax diagram and use it more effectively.
For an explanation of the conventions used in the examples in this manual,
see “Sample-Code Conventions” on page 24 of the Introduction.
Using References
For help in understanding the concepts and terminology in the SQL
statement description, check the “References” section at the end of the
description.
The “References” section points to related information in this manual and
other manuals that helps you to understand the statement in question. This
section provides some or all of the following information:
■
The names of related statements that might contain a fuller
discussion of topics in this statement
■
The titles of other manuals that provide extended discussions of
topics in this statement
■
The chapters in the Informix Guide to SQL: Tutorial that provide a taskoriented discussion of topics in this statement
Tip: If you do not have extensive knowledge and experience with SQL, the “Informix
Guide to SQL: Tutorial” gives you the basic SQL knowledge that you need to understand and use the statement descriptions in this manual.
1-8
Informix Guide to SQL: Syntax
How to Enter SQL Comments
How to Enter SQL Comments
You can add comments to clarify the purpose or effect of particular SQL statements. Your comments can help you or others to understand the role of the
statement within a program, stored procedure, or command file. The code
examples in this manual sometimes include comments that clarify the role of
an SQL statement within the code.
The following table shows the SQL comment symbols that you can enter in
your code. A Y in a column signifies that you can use the symbol with the
product or database type named in the column heading. An N in a column
signifies that you cannot use the symbol with the product or database type
that the column heading names.
Comment
Symbol
SQL
APIs
Stored
Procedures
(SPL)
DB-Access ANSICompliant
Databases
Databases
That Are
Not ANSI
Compliant
Description
double
dash
(--)
Y
Y
Y
Y
Y
The double dash precedes the
comment. The double dash can
comment only a single line. If
you want to use the double dash
to comment more than one line,
you must put the double dash at
the beginning of each comment
line.
curly
brackets
({})
N
Y
Y
Y
Y
Curly brackets enclose the
comment. The { precedes the
comment, and the } follows the
comment. You can use curly
brackets for single-line
comments or for multiple-line
comments.
SQL Statements 1-9
How to Enter SQL Comments
If the product that you are using supports both comment symbols, your
choice of a comment symbol depends on your requirements for ANSI
compliance:
■
The double dash (--) complies with the ANSI SQL standard.
■
Curly brackets ({}) are an Informix extension to the standard.
If ANSI compliance is not an issue, your choice of comment symbols is a matter of personal preference.
You can use either comment symbol when you enter SQL statements with the
SQL editor and when you create SQL command files with the SQL editor or a
system editor. An SQL command file is an operating-system file that contains
one or more SQL statements. Command files are also known as command
scripts. For more information about command files, see the discussion of
command scripts in the Informix Guide to SQL: Tutorial. For information on
creating and modifying command files with the SQL editor or a system editor
in DB-Access, see the DB-Access User Manual. ♦
D/B
You can use either comment symbol in any line of a stored procedure. See
“Adding Comments to the Procedure” on page 1-138 for further information.
Also see the discussion of commenting and documenting a procedure in the
Informix Guide to SQL: Tutorial. ♦
SPL
ESQL
You can use the double dash (--) to comment SQL statements in your SQL API.
See the manual for your SQL API for further information on the use of SQL
comment symbols and language-specific comment symbols in application
programs. ♦
Examples of SQL Comment Symbols
Some simple examples can help to illustrate the different ways of using the
SQL comment symbols.
Examples of the Double-Dash Symbol
The following example shows the use of the double dash (--) to comment an
SQL statement. In this example, the comment appears on the same line as the
statement.
SELECT * FROM customer -- Selects all columns and rows
1-10
Informix Guide to SQL: Syntax
How to Enter SQL Comments
In the following example, the user enters the same SQL statement and the
same comment as in the preceding example, but the user places the comment
on a line by itself:
SELECT * FROM customer
-- Selects all columns and rows
In the following example, the user enters the same SQL statement as in the
preceding example but now enters a multiple-line comment:
SELECT * FROM customer
-- Selects all columns and rows
-- from the customer table
Examples of the Curly-Brackets Symbols
D/B
SPL
The following example shows the use of curly brackets ({}) to comment an
SQL statement. In this example, the comment appears on the same line as the
statement.
SELECT * FROM customer {Selects all columns and rows}
In the following example, the user enters the same SQL statement and the
same comment as in the preceding example but places the comment on a line
by itself:
SELECT * FROM customer
{Selects all columns and rows}
In the following example, the user enters the same SQL statement as in the
preceding example but enters a multiple-line comment:
SELECT * FROM customer
{Selects all columns and rows
from the customer table}
♦
Non-ASCII Characters in SQL Comments
GLS
You can enter non-ASCII characters (including multibyte characters) in SQL
comments if your locale supports a code set with the non-ASCII characters.
See the Guide to GLS Functionality for further information on the GLS aspects
of SQL comments. ♦
SQL Statements 1-11
Categories of SQL Statements
Categories of SQL Statements
SQL statements are divided into the following categories:
■
Data definition statements
■
Data manipulation statements
■
Cursor manipulation statements
■
Dynamic management statements
■
Data access statements
■
Data integrity statements
■
Query optimization information statements
■
Stored procedure statements
■
Auxiliary statements
■
Client/server connection statements
■
Optical statements
The specific statements for each category are as follows.
Data Definition Statements
ALTER FRAGMENT
ALTER INDEX
ALTER TABLE
CLOSE DATABASE
CREATE DATABASE
CREATE INDEX
CREATE PROCEDURE
CREATE PROCEDURE FROM
CREATE ROLE
CREATE SCHEMA
CREATE SYNONYM
CREATE TABLE
CREATE TRIGGER
CREATE VIEW
DATABASE
DROP DATABASE
1-12
Informix Guide to SQL: Syntax
Categories of SQL Statements
DROP INDEX
DROP PROCEDURE
DROP ROLE
DROP SYNONYM
DROP TABLE
DROP TRIGGER
DROP VIEW
RENAME COLUMN
RENAME DATABASE
RENAME TABLE
Data Manipulation Statements
DELETE
INSERT
LOAD
SELECT
UNLOAD
UPDATE
Cursor Manipulation Statements
CLOSE
DECLARE
FETCH
FLUSH
FREE
OPEN
PUT
Dynamic Management Statements
ALLOCATE DESCRIPTOR
DEALLOCATE DESCRIPTOR
DESCRIBE
EXECUTE
EXECUTE IMMEDIATE
FREE
GET DESCRIPTOR
PREPARE
SET DESCRIPTOR
SQL Statements 1-13
Categories of SQL Statements
Data Access Statements
GRANT
GRANT FRAGMENT
LOCK TABLE
REVOKE
REVOKE FRAGMENT
SET ISOLATION
SET LOCK MODE
SET ROLE
SET SESSION AUTHORIZATION
SET TRANSACTION
UNLOCK TABLE
Data Integrity Statements
BEGIN WORK
CHECK TABLE
COMMIT WORK
CREATE AUDIT
DROP AUDIT
RECOVER TABLE
REPAIR TABLE
ROLLBACK WORK
ROLLFORWARD DATABASE
SET
SET LOG
START DATABASE
START VIOLATIONS TABLE
STOP VIOLATIONS TABLE
Query Optimization Information Statements
SET EXPLAIN
SET OPTIMIZATION
SET PDQPRIORITY
UPDATE STATISTICS
1-14
Informix Guide to SQL: Syntax
Categories of SQL Statements
Stored Procedure Statements
EXECUTE PROCEDURE
SET DEBUG FILE TO
Auxiliary Statements
INFO
OUTPUT
GET DIAGNOSTICS
WHENEVER
Client/Server Connection Statements
CONNECT
DISCONNECT
SET CONNECTION
INFORMIX-OnLine/Optical Statements
ALTER OPTICAL CLUSTER
CREATE OPTICAL CLUSTER
DROP OPTICAL CLUSTER
RELEASE
RESERVE
SET MOUNTING TIMEOUT
Important: INFORMIX-OnLine/Optical statements are described in the
“INFORMIX-OnLine/Optical User Manual.”
SQL Statements 1-15
ANSI Compliance and Extensions
ANSI Compliance and Extensions
The following lists show statements that are compliant with the ANSI SQL-92
standard at the entry level, statements that are ANSI compliant but include
Informix extensions, and statements that are Informix extensions to the ANSI
standard.
ANSI-Compliant Statements
CLOSE
COMMIT WORK
ROLLBACK WORK
SET SESSION AUTHORIZATION
SET TRANSACTION
ANSI-Compliant Statements with Informix Extensions
CREATE SCHEMA AUTHORIZATION
CREATE TABLE
CREATE VIEW
DECLARE
DELETE
EXECUTE
FETCH
GRANT
INSERT
OPEN
SELECT
SET CONNECTION
UPDATE
WHENEVER
Statements That Are Extensions to the ANSI Standard
ALLOCATE DESCRIPTOR
ALTER FRAGMENT
ALTER INDEX
ALTER OPTICAL CLUSTER
ALTER TABLE
BEGIN WORK
CHECK TABLE
1-16
Informix Guide to SQL: Syntax
ANSI Compliance and Extensions
CLOSE DATABASE
CONNECT
CREATE AUDIT
CREATE DATABASE
CREATE INDEX
CREATE OPTICAL CLUSTER
CREATE PROCEDURE
CREATE PROCEDURE FROM
CREATE ROLE
CREATE SYNONYM
CREATE TRIGGER
DATABASE
DEALLOCATE DESCRIPTOR
DESCRIBE
DISCONNECT
DROP AUDIT
DROP DATABASE
DROP INDEX
DROP OPTICAL CLUSTER
DROP PROCEDURE
DROP ROLE
DROP SYNONYM
DROP TABLE
DROP TRIGGER
DROP VIEW
EXECUTE IMMEDIATE
EXECUTE PROCEDURE
FLUSH
FREE
GET DESCRIPTOR
GET DIAGNOSTICS
GRANT FRAGMENT
INFO
LOAD
LOCK TABLE
OUTPUT
PREPARE
PUT
RECOVER TABLE
RELEASE
RENAME COLUMN
RENAME DATABASE
RENAME TABLE
RESERVE
SQL Statements 1-17
Statements
REVOKE
REVOKE FRAGMENT
ROLLFORWARD DATABASE
SET
SET DATASKIP
SET DEBUG FILE TO
SET DESCRIPTOR
SET EXPLAIN
SET ISOLATION
SET LOCK MODE
SET LOG
SET OPTIMIZATION
SET PDQPRIORITY
SET ROLE
SET TRANSACTION
START DATABASE
START VIOLATIONS TABLE
STOP VIOLATIONS TABLE
UNLOAD
UNLOCK TABLE
UPDATE STATISTICS
Statements
This section gives comprehensive reference descriptions of SQL statements.
The statement descriptions appear in alphabetical order. For an explanation
of the structure of statement descriptions, see “How to Enter SQL Statements” on page 1-6.
1-18
Informix Guide to SQL: Syntax
ALLOCATE DESCRIPTOR
ALLOCATE DESCRIPTOR
Use the ALLOCATE DESCRIPTOR statement to allocate memory for a systemdescriptor area. A descriptor parameter or a descriptor variable parameter
identifies the system-descriptor area. This statement creates a place in
memory to hold information that a DESCRIBE statement obtains or to hold
information about the WHERE clause of a statement.
Syntax
+
ESQL
ALLOCATE
DESCRIPTOR
' descriptor '
descriptor
variable
WITH MAX
occurrences
occurrences
variable
Element
descriptor
Purpose
Quoted string that identifies a
system-descriptor area
descriptor
variable
Host-variable name that
identifies a system-descriptor
area
Restrictions
Use single quotes. String must
represent the name of an
unallocated system-descriptor
area.
Variable must contain the name
of an unallocated systemdescriptor area.
occurrences
The number of item descriptors
in the system-descriptor area
Host variable that contains the
number of occurrences
Value must be unsigned
INTEGER. Default value is 100.
Data type must be INTEGER or
SMALLINT.
occurrences
variable
Syntax
Quoted String,
p. 1-757
Name must conform
to language-specific
rules for variable
names.
Literal Number,
p. 1-752
Name must conform
to language-specific
rules for variable
names.
SQL Statements 1-19
ALLOCATE DESCRIPTOR
Usage
The ALLOCATE DESCRIPTOR statement creates a system-descriptor area. The
descriptor parameter or the descriptor variable parameter identifies this area.
A system-descriptor area contains one or more fields called item descriptors.
Each item descriptor holds a data value that the database server can receive
or send. The item descriptors also contain information about the data such as
type, length, scale, precision, and nullability.
Either the occurrences parameter or the occurrences variable parameter specifies
the number of item descriptors that you want in the system descriptor area.
Initially, all fields in the item-descriptor area are undefined. The COUNT field
is set to the number of occurrences that you specified in the occurrences
parameter or the occurrences variable parameter. The TYPE field, the LENGTH
field, and other fields in the item descriptor are set when a DESCRIBE
statement is executed using the system descriptor. The DESCRIBE statement
also allocates memory for the DATA field in each item descriptor, based on the
TYPE and LENGTH information. You can also use item descriptors with stored
procedures. A DESCRIBE statement obtains information for the stored procedures. See Chapter 2, “SPL Statements,” for more information about stored
procedures.
If the name that you assign to a system-descriptor area matches the name of
an existing system-descriptor area, the database server returns an error. If
you free the descriptor with the DEALLOCATE DESCRIPTOR statement, you
can reuse the descriptor.
The WITH MAX Clause
You can use the optional WITH MAX occurrences clause to indicate the number
of value descriptors you need. This number must be greater than zero. When
you do not specify the WITH MAX clause, the database server uses a default
value of 100 for the occurrences parameter.
The following examples show the ALLOCATE DESCRIPTOR statement for two
SQL APIs. Each example includes the WITH MAX clause.
1-20
Informix Guide to SQL: Syntax
ALLOCATE DESCRIPTOR
In each pair of examples, the first line uses an embedded variable name to
identify the system-descriptor area, and the second line uses a quoted string
to identify the system-descriptor area. In addition, in each pair of examples,
the first line uses an embedded variable name to specify the desired number
of item descriptors, and the second line uses an unsigned integer to specify
the desired number of item descriptors.
INFORMIX-ESQL⁄C
EXEC SQL allocate descriptor :descname with max :occ;
EXEC SQL allocate descriptor 'desc1' with max 3;
INFORMIX-ESQL⁄COBOL
EXEC SQL ALLOCATE DESCRIPTOR :DESCNAME WITH MAX :OCC END-EXEC.
EXEC SQL ALLOCATE DESCRIPTOR 'DESC1' WITH MAX 3 END-EXEC.
References
See the DEALLOCATE DESCRIPTOR, DECLARE, DESCRIBE, EXECUTE, FETCH,
GET DESCRIPTOR, OPEN, PREPARE, PUT, and SET DESCRIPTOR statements in
this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of system-descriptor
areas in Chapter 5.
SQL Statements 1-21
ALTER FRAGMENT
ALTER FRAGMENT
Use the ALTER FRAGMENT statement to alter an existing table or index
fragmentation strategy dynamically as well as to create fragments initially.
Syntax
=+
OL
+
ALTER FRAGMENT ON
TABLE
surviving table
INDEX
surviving index
ATTACH
Clause
p. 1-25
DETACH
Clause
p. 1-29
INIT
Clause
p. 1-30
ADD
Clause
p. 1-37
DROP
Clause
p. 1-39
MODIFY
Clause
p. 1-40
Element
Purpose
surviving index The index on which you execute
the ALTER FRAGMENT statement
surviving table The table on which you execute
the ALTER FRAGMENT statement
1-22
Informix Guide to SQL: Syntax
Restrictions
The index must exist at the time
you execute the statement.
The table must exist at the time
you execute the statement.
Syntax
Index Name,
p. 1-741
Table Name,
p. 1-768
ALTER FRAGMENT
Usage
You can alter the fragmentation strategy of an existing table or index, or you
can create a new fragmentation strategy for nonfragmented tables. Use the
ALTER FRAGMENT statement to tune your fragmentation strategy. The
clauses of the ALTER FRAGMENT statement let you perform the following
tasks.
Clause
Purpose
ATTACH
Combines tables that contain identical table structures into a single
fragmented table.
DETACH
Detaches a table fragment from a fragmentation strategy and place
it in a new table.
INIT
Defines and initializes a new fragmentation strategy on a
nonfragmented table or converts an existing fragmentation
strategy on a fragmented table. You can also use this clause to
change the order of evaluation of fragment expressions.
ADD
Adds an additional fragment to an existing fragmentation list.
DROP
Drops an existing fragment from a fragmentation list.
MODIFY
Changes an existing fragmentation expression.
You must have the Alter or the DBA privilege to change the fragmentation
strategy of a table. You must have the Index or the DBA privilege to alter the
fragmentation strategy of an index.
The ALTER FRAGMENT statement applies only to table or index fragments
that are located at the current site. No remote information is accessed or
updated.
INIT and ATTACH are the only operations you can perform for tables and
indexes that are not already fragmented.
You cannot use the ALTER FRAGMENT statement on a temporary table or a
view.
SQL Statements 1-23
ALTER FRAGMENT
How Is the ALTER FRAGMENT Statement Executed?
If your database uses logging, the ALTER FRAGMENT statement is executed
within a single transaction. When the fragmentation strategy uses large
numbers of records, you might run out of log space or disk space
(INFORMIX-OnLine Dynamic Server requires extra disk space for the
operation; it later frees the disk space).
Making More Space
When you run out of log space or disk space, try one of the following
procedures to make more space available:
■
Turn off logging and turn it back on again at the end of the operation.
This procedure indirectly requires a backup of the root dbspace.
For more information about the ontape utility to start and stop
logging, see the INFORMIX-OnLine Dynamic Server Administrator’s
Guide. You can also use the ON-Archive utility to back up the root
dbspace. For more information about ON-Archive, see the
INFORMIX-OnLine Dynamic Server Archive and Backup Guide.
■
Split the operations into multiple ALTER FRAGMENT statements,
moving a smaller portion of records at each time.
See the INFORMIX-OnLine Dynamic Server Administrator’s Guide for information about log-space requirements and disk-space requirements. That
guide also contains detailed instructions about how to turn off logging.
Determining the Number of Rows in the Fragment
You can place as many rows into a fragment as the available space in the
dbspace allows. To find out how many rows are in a fragment, perform these
simple steps:
1-24
1.
Run the UPDATE STATISTICS statement on the table. This step fills the
sysfragments system catalog table with the current table
information.
2.
Query the sysfragments system catalog table to examine the npused
and nrows fields. The npused field gives you the number of data
pages used in the fragment, and the nrows field gives you the
number of rows in the fragment.
Informix Guide to SQL: Syntax
ALTER FRAGMENT
The ATTACH Clause
Important: Use the CREATE TABLE statement or the ALTER FRAGMENT INIT
statement to create fragmented tables.
Use the ATTACH clause to combine tables that contain identical table
structures into a fragmentation strategy. Transforming tables with identical
table structures into fragments in a single table allows OnLine to manage the
fragmentation instead of the application managing the fragmentation. The
distribution scheme can be either round-robin or expression based.
ATTACH
Clause
,
consumed table
ATTACH
,
AS frag-expression
BEFORE
surviving table
AFTER
AS frag-expression
Element
consumed table
dbspace
dbspace
1
AS REMAINDER
Purpose
A nonfragmented table on
which you execute the ATTACH
clause
Restrictions
Syntax
The table must exist at the time Table Name, p. 1-768
you execute the statement. No
serial columns, referential
constraints, primary-key
constraints, or unique
constraints are allowed in the
table. The table can have check
constraints and not null
constraints, but these constraints
are dropped after the ATTACH
clause is executed.
The dbspace name that specifies The dbspace must exist at the
Identifier, p. 1-723
where the consumed table
time you execute the statement.
expression occurs in the
fragmentation list
(1 of 2)
SQL Statements 1-25
ALTER FRAGMENT
Any tables that you attach must have been created previously in separate
dbspaces. You cannot attach the same table more than once. You cannot
attach a fragmented table to another fragmented table.
You must be the DBA or the owner of the tables that are involved to use the
ATTACH clause.
You cannot attach temporary tables.
After the tables are attached, the consumed table that is specified on the
ATTACH clause no longer exists. The records that were in the consumed table
must be referenced through the surviving table that is specified in the ALTER
FRAGMENT ON TABLE statement.
Each table that is described in the ATTACH clause must be identical in
structure; that is, all column definitions must match. The number, names,
data types, and relative position of the columns must be identical. However,
you cannot attach tables that contain serial columns. In addition, indexes and
triggers on the surviving table survive the ATTACH, but indexes and triggers
on the consumed table are dropped. Triggers are not activated with the
ATTACH clause.
1-26
Informix Guide to SQL: Syntax
ALTER FRAGMENT
Combining Identically Structured Nonfragmented Tables
To make a single, fragmented table from two or more nonfragmented tables,
the ATTACH clause must contain the surviving table as the first element of the
attach list. The attach list is the list of tables in the ATTACH clause. For
example, if you attach the tables cur_acct and new_acct, which were previously created in separate dbspaces, the surviving table cur_acct must be the
first element in the attach list. The following statement illustrates this rule:
ALTER FRAGMENT ON TABLE cur_acct ATTACH cur_acct, new_acct
If you want a new rowid column on the single fragmented table, attach all
tables first and then add the rowid with the ALTER TABLE statement.
Attaching a Nonfragmented Table to a Fragmented Table
To attach a nonfragmented table to an already fragmented table, the
nonfragmented table must have been created in a separate dbspace and must
have the same table structure as the fragmented table. The following example
shows how to attach a nonfragmented table, old_acct, which was previously
created in dbsp3, to a fragmented table, cur_acct:
ALTER FRAGMENT ON TABLE cur_acct ATTACH old_acct
The BEFORE and AFTER Clauses
The BEFORE and AFTER clauses allow you to place a new fragment in a
dbspace either before or after an existing dbspace. Use the BEFORE and
AFTER clauses only when the distribution scheme is expression based (not
round-robin). Attaching a new fragment without an explicit BEFORE or
AFTER clause places the added fragment at the end of the fragmentation list.
You cannot attach a new fragment after the remainder fragment.
Using ATTACH to Fragment Tables: Round-Robin
The following example combines nonfragmented tables pen_types and
pen_makers into a single, fragmented table, pen_types. Table pen_types
resides in dbspace dbsp1, and table pen_makers resides in dbspace dbsp2.
Table structures are identical in each table.
ALTER FRAGMENT ON TABLE pen_types
ATTACH pen_types, pen_makers
SQL Statements 1-27
ALTER FRAGMENT
After you execute the ATTACH clause, OnLine fragments the table pen_types
round-robin into two dbspaces: the dbspace that contained pen_types and
the dbspace that contained pen_makers. Table pen_makers is consumed,
and no longer exists; all rows that were in table pen_makers are now in table
pen_types.
Using ATTACH to Fragment Tables: Fragment Expression
Consider the following example that combines tables cur_acct and new_acct
and uses an expression-based distribution scheme. Table cur_acct was originally created as a fragmented table and has fragments in dbspaces dbsp1 and
dbsp2. The first statement of the example shows that table cur_acct was
created with an expression-based distribution scheme. The second statement
of the example creates table new_acct in dbsp3 without a fragmentation
strategy. The third statement combines the tables cur_acct and new_acct.
Table structures (columns) are identical in each table.
CREATE TABLE cur_acct (a int) FRAGMENT BY EXPRESSION
a < 5 in dbsp1,
a >=5 and a < 10 in dbsp2;
CREATE TABLE new_acct (a int) IN dbsp3;
ALTER FRAGMENT ON TABLE cur_acct ATTACH new_acct AS a>=10;
When you examine the sysfragments system catalog table after you have
altered the fragment, you see that table cur_acct is fragmented by expression
into three dbspaces. For additional information about the sysfragments
system catalog table, see Chapter 2 of the Informix Guide to SQL: Reference.
In addition to simple range rules, you can use the ATTACH clause to fragment
by expression with hash or arbitrary rules. For a discussion of all types of
expressions in an expression-based distribution scheme, see “The
FRAGMENT BY Clause for Tables” on page 1-35.
Warning: When you specify a date value in a fragment expression, make sure to specify 4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on the distribution scheme. When
you specify a 2-digit year, the DBCENTURY environment variable can affect the
distribution scheme and can produce unpredictable results. See the “Informix Guide
to SQL: Reference” for more information on the DBCENTURY environment variable.
1-28
Informix Guide to SQL: Syntax
ALTER FRAGMENT
What Happens to Blob Columns?
Each blob column in every table that is named in the ATTACH clause must
have the same storage type, either blobspace or tblspace. If the blob column
is a blobspace blob, the same column in all tables must be in the same
blobspace. If the blob column is a tblspace blob, the same column must be a
tblspace blob in all tables.
What Happens to Indexes and Triggers?
Unless you create separate index fragments, the index fragmentation is the
same as the table fragmentation.
When you attach tables, any indexes or triggers that are defined on the
consumed table no longer exist, and all rows in the consumed table
(new_acct) are subject to the indexes and triggers that are defined in the
surviving table (cur_acct). No triggers are activated with the ATTACH clause,
but subsequent data manipulation operations on the “new” rows can fire
triggers.
At the end of the ATTACH operation, indexes on the surviving table that were
explicitly given a fragmentation strategy remain intact with that
fragmentation strategy.
The DETACH Clause
Use the DETACH clause to detach a table fragment from a distribution scheme
and place the contents into a new nonfragmented table. See “The
FRAGMENT BY Clause for Tables” on page 1-35 for an explanation of
distribution schemes.
DETACH
Clause
DETACH
dbspace-name
new table
SQL Statements 1-29
ALTER FRAGMENT
Element
dbspace-name
new table
Purpose
The name of the dbspace that
contains the fragment to be
detached
The table that results after you
execute the ALTER FRAGMENT
statement
Restrictions
The dbspace must exist when
you execute the statement.
Syntax
Identifier, p. 1-723
The table must not exist before
you execute the statement.
Table Name, p. 1-768
The DETACH clause cannot be applied to a table if that table is the parent of
a referential constraint or if a rowid column is defined on the table.
The new table that results from the execution of the DETACH clause does not
inherit any indexes or constraints from the original table. Only the data
remains.
The following example shows the table cur_acct fragmented into two
dbspaces, dbsp1 and dbsp2:
ALTER FRAGMENT ON TABLE cur_acct DETACH dbsp2 accounts
This example detaches dbsp2 from the distribution scheme for cur_acct and
places the rows in a new table, accounts. Table accounts now has the same
structure (column names, number of columns, data types, and so on) as table
cur_acct, but the table accounts does not contain any indexes or constraints
from the table cur_acct. Both tables are now nonfragmented.
The following example shows a table that contains three fragments:
ALTER FRAGMENT ON TABLE bus_acct DETACH dbsp3 cli_acct
This statement detaches dbsp3 from the distribution scheme for bus_acct
and places the rows in a new table, cli_acct. Table cli_acct now has the same
structure (column names, number of columns, data types, and so on) as
bus_acct, but the table cli_acct does not contain any indexes or constraints
from the table bus_acct. Table cli_acct is a nonfragmented table, and table
bus_acct remains a fragmented table.
The INIT Clause
Use the INIT clause to perform the following functions:
■
1-30
Change the fragmentation strategy on a single, fragmented table
including changing the order of evaluating fragment expressions
Informix Guide to SQL: Syntax
ALTER FRAGMENT
■
Define and initialize a new fragmentation strategy on a
nonfragmented table
■
Convert a fragmented table to a nonfragmented table
■
Detach an index from a table fragmentation strategy
INIT
Clause
FRAGMENT BY
Clause
for Tables
INIT
WITH ROWIDS
FRAGMENT BY
Clause
for Indexes
FRAGMENT BY
Clause
for Tables
IN dbspace
,
FRAGMENT BY
ROUND ROBIN IN
dbspace
,
dbspace
,
EXPRESSION
frag-expression
IN dbspace
,
frag-expression
IN dbspace
REMAINDER IN
remainder dbspace
,
FRAGMENT BY
Clause
for Indexes
,
FRAGMENT BY
EXPRESSION
frag-expression
IN dbspace
,
frag-expression
IN dbspace
,
REMAINDER IN
remainder dbspace
SQL Statements 1-31
ALTER FRAGMENT
Element
dbspace
Purpose
The dbspace that contains the
fragmented information
frag-expression
remainder
dbspace
Restrictions
The dbspace must exist at the
time you execute the statement.
When you use the FRAGMENT
BY clause, you must specify at
least two dbspaces. You can
specify a maximum of 2,048
dbspaces.
An expression that defines a
If you specify a value for
fragment using a range, hash, or remainder dbspace, you must
arbitrary rule
specify at least one fragment
expression. If you do not specify
a value for remainder dbspace,
you must specify at least two
fragment expressions. You can
specify a maximum of 2,048
fragment expressions. Each
fragment expression can contain
only columns from the current
table and only data values from
a single row. No subqueries,
stored procedures, current
date/time functions, or
aggregates are allowed in
frag-expression.
The dbspace that contains data If you specify two or more
that does not meet the
fragment expressions, remainder
conditions defined in any
dbspace is optional. If you
fragment expression.
specify only one fragment
expression, remainder dbspace is
required. The dbspace that is
specified in remainder dbspace
must exist at the time you
execute the statement.
Syntax
Identifier, p. 1-723
Condition, p. 1-643,
and Expression,
p. 1-671
Identifier, p. 1-723
The INIT clause allows you to fragment an existing table or index that is not
fragmented without redefining the table or index. With the INIT clause, you
can also convert an existing fragmentation strategy on a table or index to
another fragmentation strategy. Any existing fragmentation strategy is
discarded, and records are moved to fragments as defined in the new
fragmentation strategy. The INIT clause also allows you to convert a
fragmented table or index to a nonfragmented table or index.
1-32
Informix Guide to SQL: Syntax
ALTER FRAGMENT
When you use the INIT clause to fragment an existing nonfragmented table,
all indexes on the table become fragmented in the same way as the table.
Changing an Existing Fragmentation Strategy on a Single Table
You can redefine a fragmentation strategy if you decide that your initial
strategy does not fulfill your needs. The following example shows the
statement that originally defined the fragmentation strategy on the table
account and then shows the ALTER FRAGMENT statement that redefines the
fragmentation strategy:
CREATE TABLE account (col1 int, col2 int)
FRAGMENT BY ROUND ROBIN IN dbsp1, dbsp2;
ALTER FRAGMENT ON TABLE account
INIT FRAGMENT BY EXPRESSION
MOD(col1, 3) = 0 in dbsp1,
MOD(col1, 3) = 1 in dbsp2,
MOD(col1, 3) = 2 in dbsp3;
When you want to redefine a fragmentation strategy, and any existing
dbspaces are full, you must fragment the table in different dbspaces than the
full dbspaces.
Fragmenting Unique and System Indexes
You can fragment unique indexes only if the table uses an expression-based
distribution scheme. The columns that are referenced in the fragment
expression must be indexed columns. If your ALTER FRAGMENT INIT
statement fails to meet either of these restrictions, the INIT fails, and work is
rolled back.
You might have an attached unique index on a table fragmented by Column
A. If you use INIT to change the table fragmentation to Column B, the INIT
fails because the unique index is defined on Column A. To resolve this issue,
you can use the INIT clause on the index to detach it from the table fragmentation strategy and fragment it separately.
System indexes (such as those used in referential constraints and unique
constraints) utilize user indexes if the indexes exist. If no user indexes can be
utilized, system indexes remain nonfragmented and are moved to the
dbspace where the database was created. To fragment a system index, create
the fragmented index on the constraint columns, and then use the ALTER
TABLE statement to add the constraint.
SQL Statements 1-33
ALTER FRAGMENT
Converting a Fragmented Table to a Nonfragmented Table
You might decide that you no longer want a table to be fragmented. You can
use the INIT clause to convert a fragmented table to a nonfragmented table.
The following example shows the original fragmentation definition as well as
how to use the ALTER FRAGMENT statement to convert the table:
CREATE TABLE checks (col1 int, col2 int)
FRAGMENT BY ROUND ROBIN IN dbsp1, dbsp2, dbsp3;
ALTER FRAGMENT ON TABLE checks INIT IN dbsp1;
You must use the IN dbspace clause to place the table in a dbspace explicitly.
When you use the INIT clause to change a fragmented table to a
nonfragmented table (that is, to rid the table of any fragmentation strategy),
all indexes that are fragmented in the same way as the table become nonfragmented indexes. Similarly, system indexes that do not utilize user indexes
become nonfragmented indexes and are moved from the database dbspace to
the table dbspace. If any system indexes use detached user indexes, the
system indexes are not affected by the use of the INIT clause on the table.
Defining a Fragmentation Strategy on a Nonfragmented Table
You can use the INIT clause to define a fragmentation strategy on a
nonfragmented table. It does not matter whether the table was created with
a storage option. The following example shows the original table definition
as well as how to use the ALTER FRAGMENT statement to fragment the table:
CREATE TABLE balances (col1 int, col2 int) IN dbsp1;
ALTER FRAGMENT ON TABLE balances INIT
FRAGMENT BY EXPRESSION
col1 <= 500 IN dbsp1,
col1 > 500 and col1 <=1000 IN dbsp2,
REMAINDER IN dbsp3;
Detaching an Index from a Table-Fragmentation Strategy
You can detach an index from a table-fragmentation strategy with the INIT
clause, which causes an attached index to become a detached index. This
breaks any dependency of the index on the table fragmentation strategy.
1-34
Informix Guide to SQL: Syntax
ALTER FRAGMENT
The WITH ROWIDS Clause
Nonfragmented tables contain a pseudocolumn called the rowid column.
Fragmented tables do not contain this column unless it is explicitly created.
Use the WITH ROWIDS clause to add a new column called the rowid column.
OnLine assigns a unique number to each row that remains stable for the
existence of the row. The database server creates an index that it uses to find
the physical location of the row. Each row contains an additional 4 bytes to
store the rowid column after you add the WITH ROWIDS clause.
Important: Informix recommends that you use primary keys, rather than the rowid
column, as an access method.
The FRAGMENT BY Clause for Tables
Use the FRAGMENT BY clause for tables to define the distribution scheme,
which is either round-robin or expression based.
In a round-robin distribution scheme, specify at least two dbspaces where the
fragments are placed. As records are inserted into the table, they are placed
in the first available dbspace. OnLine balances the load between the specified
dbspaces as you insert records and distributes the rows so that the fragments
always maintain approximately the same number of rows. In this distribution scheme, the database server must scan all fragments when it searches
for a row.
In an expression-based distribution scheme, each fragment expression in a
rule specifies a dbspace. The rule specifies how you determine the fragment
into which rows are placed. Each fragment expression within the rule isolates
data and aids the database server in searching for rows. You can specify one
of the following rules:
■
Range rule
A range rule specifies fragment expressions that use a range to
specify which rows are placed in a fragment, as shown in the
following example:
...
FRAGMENT BY EXPRESSION
c1 < 100 IN dbsp1,
c1 >= 100 and c1 < 200 IN dbsp2,
c1 >= 200 IN dbsp3;
SQL Statements 1-35
ALTER FRAGMENT
■
Hash rule
A hash rule specifies fragment expressions that are created when you
use a hash algorithm, which is often implemented with the MOD
function, as shown in the following example:
.
.
.
FRAGMENT BY
MOD(id_num,
MOD(id_num,
MOD(id_num,
■
EXPRESSION
3) = 0 IN dbsp1,
3) = 1 IN dbsp2,
3) = 2 IN dbsp3;
Arbitrary rule
An arbitrary rule specifies fragment expressions based on a
predefined SQL expression that typically includes the use of OR
clauses to group data, as shown in the following example:
.
.
.
FRAGMENT BY EXPRESSION
zip_num = 95228 OR zip_num = 95443 IN dbsp2,
zip_num = 91120 OR zip_num = 92310 IN dbsp4,
REMAINDER IN dbsp5;
Warning: When you define the distribution scheme for a table and specify a date
value in a fragment expression, make sure to specify 4 digits instead of 2 digits for
the year. When you specify a 4-digit year, the DBCENTURY environment variable has
no effect on the distribution scheme. When you specify a 2-digit year, the
DBCENTURY environment variable can affect the distribution scheme and can
produce unpredictable results. See the “Informix Guide to SQL: Reference” for more
information on the DBCENTURY environment variable.
The FRAGMENT BY Clause for Indexes
Use the FRAGMENT BY clause for indexes to define the expression-based
distribution scheme. Like the FRAGMENT BY clause for tables, the
FRAGMENT BY clause for indexes supports range rules, hash rules, and
arbitrary rules. See “The FRAGMENT BY Clause for Tables” on page 1-35 for
an explanation of these rules.
1-36
Informix Guide to SQL: Syntax
ALTER FRAGMENT
Warning: When you define the distribution scheme for an index and specify a date
value in a fragment expression, make sure to specify 4 digits instead of 2 digits for
the year. When you specify a 4-digit year, the DBCENTURY environment variable has
no effect on the distribution scheme. When you specify a 2-digit year, the
DBCENTURY environment variable can affect the distribution scheme and can
produce unpredictable results. See the “Informix Guide to SQL: Reference” for more
information on the DBCENTURY environment variable.
The ADD Clause
Use the ADD clause to add another fragment to an existing fragmentation list.
ADD
Clause
ADD
new dbspace
frag-expression IN new dbspace
BEFORE
existing dbspace
AFTER
REMAINDER IN new dbspace
Element
Purpose
existing dbspace A dbspace name specified in an
existing fragmentation list
frag-expression The range, hash, or arbitrary
expression that defines the
added fragment
new dbspace
The added dbspace in a roundrobin distribution scheme
Restrictions
The dbspace must exist at the
time you execute the statement.
The frag-expression can contain
only columns from the current
table and only data values from
a single row. No subqueries,
stored procedures, current
date/time functions, or
aggregates are allowed in
frag-expression.
The dbspace must exist at the
time you execute the statement.
Syntax
Identifier, p. 1-723
Condition, p. 1-643,
and Expression,
p. 1-671
Identifier, p. 1-723
SQL Statements 1-37
ALTER FRAGMENT
Adding a New Dbspace to a Round-Robin Distribution Scheme
You can add more dbspaces to a round-robin distribution scheme. The
following example shows the original round-robin definition:
CREATE TABLE book (col1 int, col2 title)
FRAGMENT BY ROUND ROBIN in dbsp1, dbsp4;
To add another dbspace, use the ADD clause, as shown in the following
example:
ALTER FRAGMENT ON TABLE book ADD dbsp3;
Adding Fragment Expressions
Adding a fragment expression to the fragmentation list in an expressionbased distribution scheme can shuffle records from some existing fragments
into the new fragment. When you add a new fragment into the middle of the
fragmentation list, all the data existing in fragments after the new one must
be re-evaluated. The following example shows the original expression
definition:
.
.
.
FRAGMENT BY EXPRESSION
c1 < 100 IN dbsp1,
c1 >= 100 and c1 < 200 IN dbsp2,
REMAINDER IN dbsp3;
If you want to add another fragment to the fragmentation list and have this
fragment hold rows between 200 and 300, use the following ALTER
FRAGMENT statement:
ALTER FRAGMENT ON TABLE news ADD
c1 >= 200 and c1 < 300 IN dbsp4;
Any rows that were formerly in the remainder fragment and that fit the
criteria c1 >=200 and c1 < 300 are moved to the new dbspace.
Warning: When you specify a date value in a fragment expression, make sure to specify 4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on the distribution scheme. When
you specify a 2-digit year, the DBCENTURY environment variable can affect the
distribution scheme and can produce unpredictable results. See the “Informix Guide
to SQL: Reference” for more information on the DBCENTURY environment variable.
1-38
Informix Guide to SQL: Syntax
ALTER FRAGMENT
The BEFORE and AFTER Clauses
The BEFORE and AFTER clauses allow you to place a new fragment in a
dbspace either before or after an existing dbspace. Use the BEFORE and
AFTER clauses only when the distribution scheme is expression based (not
round-robin). You cannot add a new fragment after the remainder fragment.
Adding a new fragment without an explicit BEFORE or AFTER clause places
the added fragment at the end of the fragmentation list. However, if the
fragmentation list contains a REMAINDER clause, the added fragment is
added before the remainder fragment (that is, the remainder remains the last
item on the fragment list).
The REMAINDER Clause
You cannot add a remainder fragment when one already exists. When you
add a new fragment to the end of the fragmentation list, and a remainder
fragment exists, the records in the remainder fragment are retrieved and reevaluated. These records can be moved to the new fragment. The remainder
fragment always remains the last item in the fragment list.
The DROP Clause
Use the DROP clause to drop an existing fragment from a fragmentation list.
DROP
Clause
DROP
Element
dbspace-name
dbspace-name
Purpose
The name of the dbspace that
contains the dropped fragment
Restrictions
Syntax
The dbspace must exist at the
Identifier, p. 1-723
time you execute the statement.
You cannot drop one of the fragments when the table contains only two
fragments. You cannot drop a fragment in a table that is fragmented with an
expression-based distribution scheme if the fragment contains data that
cannot be moved to another fragment. If the distribution scheme contains a
REMAINDER clause, or if the expressions were constructed in an overlapping
manner, you can drop a fragment that contains data.
SQL Statements 1-39
ALTER FRAGMENT
When you want to make a fragmented table nonfragmented, use either the
INIT or DETACH clause.
When you drop a fragment from a dbspace, the underlying dbspace is not
affected. Only the fragment data within that dbspace is affected. When you
drop a fragment all the records located in the fragment move to another
fragment. The destination fragment might not have enough space for the
additional records. When this happens, follow one of the procedures that are
listed in “Making More Space” on page 1-24 to increase your space, and retry
the procedure.
The following examples show how to drop a fragment from a fragmentation
list. The first line shows how to drop an index fragment, and the second line
shows how to drop a table fragment.
ALTER FRAGMENT ON INDEX cust_indx DROP dbsp2;
ALTER FRAGMENT ON TABLE customer DROP dbsp1;
The MODIFY Clause
Use the MODIFY clause to change an existing fragment expression on an
existing dbspace. You can also use the MODIFY clause to move a fragment
expression from one dbspace to a different dbspace.
MODIFY
Clause
,
MODIFY
mod-dbspace
TO
frag-expression IN new-dbspace
1
1-40
Informix Guide to SQL: Syntax
REMAINDER IN new-dbspace
ALTER FRAGMENT
Element
frag-expression
Purpose
The modified range, hash, or
arbitrary expression
mod-dbspace
The modified dbspace
new-dbspace
The dbspace that contains the
modified information
Restrictions
The fragment expression can
contain only columns from the
current table and only data
values from a single row. No
subqueries, stored procedures,
current date/time functions, or
aggregates are allowed in
frag-expression.
The dbspace must exist when
you execute the statement.
The dbspace must exist when
you execute the statement.
Syntax
Condition, p. 1-643,
and Expression,
p. 1-671
Identifier, p. 1-723
Identifier, p. 1-723
General Usage
When you use the MODIFY clause, the underlying dbspaces are not affected.
Only the fragment data within the dbspaces is affected.
You cannot change a REMAINDER fragment into a nonremainder fragment if
records within the REMAINDER fragment do not pass the new expression.
Warning: When you specify a date value in a fragment expression in the MODIFY
clause, make sure to specify 4 digits instead of 2 digits for the year. When you specify
a 4-digit year, the DBCENTURY environment variable has no effect on the distribution scheme. When you specify a 2-digit year, the DBCENTURY environment
variable can affect the distribution scheme and can produce unpredictable results. See
the “Informix Guide to SQL: Reference” for more information on the DBCENTURY
environment variable.
Changing the Expression in an Existing Dbspace
When you use the MODIFY clause to change an expression without changing
the dbspace storage for the expression, you must use the same name for the
mod dbspace and the new dbspace.
The following example shows how to use the MODIFY clause to change an
existing expression:
ALTER FRAGMENT ON TABLE cust_acct
MODIFY dbsp1 to acct_num < 65 IN dbsp1
SQL Statements 1-41
ALTER FRAGMENT
Moving an Expression from One Dbspace to Another
When you use the MODIFY clause to move an expression from one dbspace
to another, mod-dbspace is the name of the dbspace where the expression was
previously located, and new-dbspace is the new location for the expression.
The following example shows how to use the MODIFY clause to move an
expression from one dbspace to another:
ALTER FRAGMENT ON TABLE cust_acct
MODIFY dbsp1 to acct_num < 35 in dbsp2
In this example, the distribution scheme for the cust_acct table is modified so
that all row items in the column acct_num that are less than 35 are now
contained in the dbspace dbsp2. These items were formerly contained in the
dbspace dbsp1.
Changing the Expression and Moving it to a New Dbspace
When you use the MODIFY clause to change the expression and move it to a
new dbspace, change both the expression name and the dbspace name.
What Happens to Indexes?
If your indexes are attached indexes, and you modify the table, the index
fragmentation strategy is also modified.
References
See the CREATE TABLE, CREATE INDEX, ALTER TABLE statements in this
manual. Also see the Condition, Data Type, Expression, and Identifier
segments.
For a task-oriented discussion of each clause in the ALTER FRAGMENT
statement, see Chapter 9 of the Informix Guide to SQL: Tutorial.
1-42
Informix Guide to SQL: Syntax
ALTER INDEX
ALTER INDEX
Use the ALTER INDEX statement to put the data in a table in the order of an
existing index or to release an index from the clustering attribute.
Syntax
+
ALTER INDEX
Index Name
p. 1-741
TO
CLUSTER
NOT
Usage
The ALTER INDEX statement works only on indexes that are created with the
CREATE INDEX statement; it does not affect constraints that are created with
the CREATE TABLE statement.
SE
You cannot use a ROLLBACK WORK statement to undo an ALTER INDEX
statement. When you roll back a transaction that contains an ALTER INDEX
statement, the index remains altered; you do not receive an error message.
When you have an audit trail on the table, you cannot use the ALTER INDEX
statement. When you want to change an index on an audited table, you must
first drop the audit on the table, alter the index, and create a new audit for the
table. ♦
You cannot alter the index of a temporary table.
SQL Statements 1-43
ALTER INDEX
The TO CLUSTER Option
The TO CLUSTER option causes the rows in the physical table to reorder in the
indexed order.
The following example shows how you can use the ALTER INDEX TO
CLUSTER statement to order the rows in the orders table physically. The
CREATE INDEX statement creates an index on the customer_num column of
the table. Then the ALTER INDEX statement causes the physical ordering of
the rows.
CREATE INDEX ix_cust ON orders (customer_num);
ALTER INDEX ix_cust TO CLUSTER;
Reordering causes rewriting the entire file. This process can take a long time,
and it requires sufficient disk space to maintain two copies of the table.
While a table is clustering, the table is locked IN EXCLUSIVE MODE. When
another process is using the table to which index name belongs, the database
server cannot execute the ALTER INDEX statement with the TO CLUSTER
option; it returns an error unless lock mode is set to WAIT. (When lock mode
is set to WAIT, the database server retries the ALTER INDEX statement.)
Over time, if you modify the table, you can expect the benefit of an earlier
cluster to disappear because rows are added in space-available order, not
sequentially. You can recluster the table to regain performance by issuing
another ALTER INDEX TO CLUSTER statement on the clustered index. You do
not need to drop a clustered index before you issue another ALTER INDEX TO
CLUSTER statement on a currently clustered index.
1-44
Informix Guide to SQL: Syntax
ALTER INDEX
The TO NOT CLUSTER Option
The NOT option drops the cluster attribute on the index name without
affecting the physical table. Because only one clustered index per table can
exist, you must use the NOT option to release the cluster attribute from one
index before you assign it to another. The following statements illustrate how
to remove clustering from one index and how a second index physically
reclusters the table:
CREATE UNIQUE INDEX ix_ord
ON orders (order_num);
CREATE CLUSTER INDEX ix_cust
ON orders (customer_num);
.
.
.
ALTER INDEX ix_cust TO NOT CLUSTER;
ALTER INDEX ix_ord TO CLUSTER;
The first two statements create indexes for the orders table and cluster the
physical table in ascending order on the customer_num column. The last two
statements recluster the physical table in ascending order on the order_num
column.
References
See the CREATE INDEX and CREATE TABLE statements in this chapter.
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of clustered indexes.
SQL Statements 1-45
ALTER TABLE
ALTER TABLE
Use the ALTER TABLE statement to add a column to or delete a column from
a table, modify the data constraints that are placed on a column, add a
constraint to a column or a composite list of columns, drop a constraint that
is associated with a column or a composite list of columns, or change the
extent size. You can also use the ALTER TABLE statement to add a rowid
column to a fragmented table or drop a rowid column from a fragmented
table.
Syntax
,
+
ALTER TABLE
Table Name
p. 1-768
ADD Clause
p. 1-48
Synonym
Name
p. 1-766
DROP Clause
p. 1-64
MODIFY Clause
p. 1-66
ADD CONSTRAINT
Clause p. 1-69
DROP CONSTRAINT
Clause p. 1-73
OL
1
MODIFY NEXT SIZE
Clause p. 1-74
1
LOCK MODE
Clause p. 1-75
1
ADD ROWIDS
DROP ROWIDS
1-46
Informix Guide to SQL: Syntax
ALTER TABLE
Usage
To use the ALTER TABLE statement, you must meet one of the following
conditions:
■
You must have the DBA privilege on the database where the table
resides.
■
You must own the table.
■
You must have the Alter privilege on the specified table and the
Resource privilege on the database where the table resides.
You cannot alter a temporary table.
To add a referential constraint, you must have the DBA or References
privilege on either the referenced columns or the referenced table.
When you add a constraint of any type, the name of the constraint must be
unique within the database.
ANSI
When you add a constraint of any type, the owner.name combination (the
combination of the owner name and constraint name) must be unique within
the database. ♦
To drop a constraint in a database, you must have the DBA privilege or be the
owner of the constraint. If you are the owner of the constraint but not the
owner of the table, you must have Alter privilege on the specified table. You
do not need the References privilege to drop a constraint.
Altering a table on which a view depends might invalidate the view.
You can use one or more of the ADD, DROP, MODIFY, ADD CONSTRAINT, or
DROP CONSTRAINT clauses, and you can place them in any order. You can
use only one MODIFY NEXT SIZE, LOCK MODE, ADD ROWIDS, or DROP
ROWIDS clause. The actions are performed in the order that is specified. If any
of the actions fails, the entire operation is cancelled.
SE
You cannot use a ROLLBACK WORK statement to undo an ALTER TABLE
statement. When you roll back a transaction that contains an ALTER TABLE
statement, the table remains altered; you do not receive an error message. ♦
The ADD ROWIDS and DROP ROWIDS clauses apply specifically to
fragmented tables.
SQL Statements 1-47
ALTER TABLE
Restrictions for Violations and Diagnostics Tables
Keep the following considerations in mind when you use the ALTER TABLE
statement in connection with violations and diagnostics tables:
■
You cannot add, drop, or modify a column if the table that contains
the column has violations and diagnostics tables associated with it.
■
You cannot alter a violations or diagnostics table.
■
You cannot add a constraint to a violations or diagnostics table.
See the START VIOLATIONS TABLE statement on page 1-584 for further
information on violations and diagnostics tables.
ADD Clause
ADD Clause
Add Column
Clause
ADD
,
(
Add Column
Clause
)
Add Column
Clause
new
column
name
Element
column name
new column
name
1-48
Data Type
p. 1-664
DEFAULT
Clause
p. 1-51
Purpose
The name of a column before
which the new column is to be
placed
The name of the column that
you are adding
Informix Guide to SQL: Syntax
New Column
Constraint
Definition
p. 1-54
BEFORE
column
name
Restrictions
The column must already exist
in the table.
Syntax
Identifier, p. 1-723
You cannot add a SERIAL
column if the table contains
data.
Identifier, p. 1-723
ALTER TABLE
Use the ADD clause to add a column to a table. You cannot add a SERIAL
column to a table if the table contains data.
Algorithms for Adding Columns to Tables
INFORMIX-OnLine Dynamic Server uses the following two algorithms for
adding columns to tables:
■
If you execute an ALTER TABLE statement that adds a column or list
of columns to the end of a table, the database server uses an
algorithm that is known as the in-place alter algorithm. When it uses
this algorithm, the server allows the table definition to be altered
without making the table unavailable to users for longer than the
time it takes to update the table definition. Furthermore, the physical
addition of the new columns to the table definition occurs essentially
in place as rows are updated, without requiring a second copy of the
table to be created.
■
If you execute an ALTER TABLE statement that does not add a column
or list of columns to the end of a table, the database server uses a
slower algorithm. When it uses this slower algorithm, the database
server performs the alter operation by placing an exclusive lock on
the table while it copies the table to be altered to a new table that
contains the new table definition. After the copy operation is
complete, the database server drops the older version of the table.
Tip: To add a column to the end of a table, omit the BEFORE option from the ADD
clause. When you do not specify a column before which the new column is to be
added, the database server adds the new column to the end of the table by default.
Scope of the In-Place Alter Algorithm
The database server uses the in-place alter algorithm if you specify the ADD
clause without the BEFORE option and if you specify any clauses other than
the following:
■
The DROP clause
■
A MODIFY clause that changes the data type of a column or changes
the number of characters in a character column
SQL Statements 1-49
ALTER TABLE
Benefits of the In-Place Alter Algorithm
The in-place alter algorithm lets you alter tables in place instead of creating a
new table with the latest table definition and copying rows from the original
table to the new table. The in-place alter method reduces the space that is
required for altering tables and also increases the availability of the tables
that are being altered.
The database server uses the slower algorithm for altering tables whenever
your ALTER TABLE statement does not match the conditions for using the inplace alter algorithm. The database server uses the slower algorithm under
the following conditions:
1-50
■
The database server uses the slower algorithm if you specify an ADD
clause with the BEFORE option.
■
The database server uses the slower algorithm if you specify an ADD
clause without the BEFORE option, but you also specify one of the
following clauses:
❑
The DROP clause
❑
A MODIFY clause that changes the data type of a column or
changes the number of characters in a character column
Informix Guide to SQL: Syntax
ALTER TABLE
DEFAULT Clause
DEFAULT
Clause
DEFAULT
literal
NULL
CURRENT
p. 1-680
DATETIME
Field Qualifier
p. 1-669
USER
p. 1-678
TODAY
p. 1-680
SITENAME
p. 1-679
DBSERVERNAME
p. 1-679
Element
literal
Purpose
A literal term that defines alpha
or numeric constant characters
to be used as the default value
for the column
Restrictions
Term must be appropriate type
for the column. See “Literal
Terms” on page 1-52.
Syntax
Expression, p. 1-671
You specify a default value to insert into the column when you do not specify
an explicit value. When a default is not specified, and the column allows
nulls, the default is NULL. When you designate NULL as the default value for
a column, you cannot place a not null constraint on the column.
You cannot place a default on SERIAL columns.
When the altered table already has rows in it, the new column contains the
default value for all existing rows.
SQL Statements 1-51
ALTER TABLE
Literal Terms
You can designate literal terms as default values. Use a literal term to define
alpha or numeric constant characters. To use a literal term as a default value,
you must adhere to the rules in the following table.
Use a Literal
With Columns of Data Type
INTEGER
INTEGER, SMALLINT, DECIMAL, MONEY, FLOAT,
SMALLFLOAT
DECIMAL
DECIMAL, MONEY, FLOAT, SMALLFLOAT
CHARACTER
CHAR, NCHAR, NVARCHAR, VARCHAR, DATE
INTERVAL
INTERVAL
DATETIME
DATETIME
Characters must be enclosed in quotation marks. Date literals must be
formatted in accordance with the DBDATE environment variable. When
DBDATE is not set, the format mm/dd/yyyy is assumed.
For information on using a literal INTERVAL, see the Literal INTERVAL
segment on page 1-749. For more information on using a literal DATETIME,
see the Literal DATETIME segment on page 1-746.
Data-Type Requirements
The following table indicates the data type requirements for columns that
specify the CURRENT, DBSERVERNAME, SITENAME, TODAY, or USER
functions as the default value.
Function Name
Data Type Requirements
CURRENT
DATETIME column with matching qualifier
DBSERVERNAME
CHAR, NCHAR, VARCHAR, or NVARCHAR column at least
18 characters long
(1 of 2)
1-52
Informix Guide to SQL: Syntax
ALTER TABLE
Function Name
Data Type Requirements
SITENAME
CHAR, NCHAR, VARCHAR, or NVARCHAR column at least
18 characters long
TODAY
DATE column
USER
CHAR column at least 8 characters long
(2 of 2)
Example of a Literal Default Value
The following example adds a column to the items table. In items, the new
column item_weight has a literal default value:
ALTER TABLE items ADD
item_weight DECIMAL (6, 2) DEFAULT 2.00 BEFORE total_price
In this example, each existing row in the items table has a default value of
2.00 for the item_weight column.
Using Not Null Constraints with ADD
When you do not indicate a default value for a column, the default is null
unless you place a not null constraint on the column. In this case, if the not
null constraint is used, no default value exists for the column, and the column
does not allow nulls. When the table contains data, however, you cannot
specify a not null constraint when you add a column (unless both the not null
constraint and a default value other than null are specified), nor can you
specify that the new column has a unique or primary-key constraint. When
you want to add a column with a unique constraint, the table can contain a
single row of data when you issue the ALTER TABLE statement. When you
want to add a column with a not null constraint or a primary-key constraint,
the table must be empty when you issue the ALTER TABLE statement. The
following statement is valid only if the items table is empty:
ALTER TABLE items
ADD (item_weight DECIMAL(6,2) NOT NULL
BEFORE total_price)
SQL Statements 1-53
ALTER TABLE
New Column-Constraint Definition
New ColumnConstraint
Definition
UNIQUE
+
NOT
NULL
+
DISTINCT
+
ConstraintMode
Definitions
p. 1-55
PRIMARY
KEY
ConstraintMode
Definitions
p. 1-55
REFERENCES
Clause
p. 1-57
CHECK
Clause
p. 1-63
You cannot specify a unique or primary-key constraint on a new column if
the table contains data. However, in the case of a unique constraint, the table
can contain a single row of data. When you want to add a column with a
primary-key constraint, the table must be empty when you issue the ALTER
TABLE statement.
The following rules apply when you place unique or primary-key constraints
on existing columns:
1-54
■
When you place a unique or primary-key constraint on a column or
set of columns, and a unique index already exists on that column or
set of columns, the constraint shares the index. However, if the existing index allows duplicates, the database server returns an error. You
must then drop the existing index before you add the constraint.
■
When you place a unique or primary-key constraint on a column or
set of columns, and a referential constraint already exists on that
column or set of columns, the duplicate index is upgraded to unique
(if possible), and the index is shared.
Informix Guide to SQL: Syntax
ALTER TABLE
You cannot have a unique constraint on a BYTE or TEXT column, nor can you
place referential or check constraints on these types of columns. You can
place a check constraint on a BYTE or TEXT column. However, you can check
only for IS NULL, IS NOT NULL, or LENGTH.
Constraint-Mode Definitions
Constraint-Mode
Definitions
CONSTRAINT
Constraint
Name
p. 1-658
DISABLED
ENABLED
FILTERING
WITHOUT
ERROR
WITH
ERROR
You can use the Constraint-Mode Definitions option for the following
purposes:
■
You can assign a name to a constraint on a column.
■
You can set a constraint to one of the following object modes:
disabled, enabled, or filtering.
SQL Statements 1-55
ALTER TABLE
Description of Constraint Modes
You can set constraints to the following modes: disabled, enabled, or filtering.
These modes are described in the following table.
Constraint
Mode
Effect
disabled
A constraint that is created in disabled mode is not enforced during
insert, delete, and update operations.
enabled
A constraint that is created in enabled mode is enforced during
insert, delete, and update operations. If a target row causes a
violation of the constraint, the statement fails.
filtering
A constraint that is created in filtering mode is enforced during
insert, delete, and update operations. If a target row causes a
violation of the constraint, the statement continues processing, but
the bad row is written to the violations table that is associated with
the target table. Diagnostic information about the constraint
violation is written to the diagnostics table that is associated with
the target table.
If you chose the filtering mode, you can specify the WITHOUT ERROR options.
The following table describes these options.
1-56
Error Option
Effect
WITHOUT
ERROR
When a filtering mode constraint is violated during an insert,
delete, or update operation, no integrity-violation error is returned
to the user.
WITH ERROR
When a filtering mode constraint is violated during an insert,
delete, or update operation, an integrity-violation error is returned
to the user.
Informix Guide to SQL: Syntax
ALTER TABLE
Using Constraint Modes
You must observe the following rules when you use constraint modes:
■
If you do not specify the object mode of a column-level or table-level
constraint explicitly, the default mode is enabled.
■
If you do not specify the WITH ERROR or WITHOUT ERROR option for
a filtering mode constraint, the default error option is WITHOUT
ERROR.
■
When you add a column-level or table-level constraint to a table and
specify the disabled object mode for the constraint, your ALTER
TABLE statement succeeds even if existing rows in the table violate
the constraint.
■
When you add a column-level or table-level constraint to a table and
specify the enabled or filtering object mode for the constraint, your
ALTER TABLE statement succeeds if no existing rows in the table
violate the new constraint. However, if any existing rows in the table
violate the constraint, your ALTER TABLE statement fails and returns
an error.
■
When you add a column-level or table-level constraint to a table in
the enabled or filtering object mode, and existing rows in the table
violate the constraint, erroneous rows in the base table are not
filtered to the violations table. Thus, you cannot use a violations table
to detect the erroneous rows in the base table.
The REFERENCES Clause
REFERENCES
Clause
REFERENCES
table name
OL
+
,
(
column
name
)
ON DELETE CASCADE
SQL Statements 1-57
ALTER TABLE
Element
column name
table name
Purpose
A referenced column or set of
columns in the referenced table.
If the referenced table is
different from the referencing
table, the default is the primarykey column. If the referenced
table is the same as the
referencing table, there is no
default.
The name of the referenced table
Restrictions
Syntax
You must observe restrictions
Identifier, p. 1-723
on the number of columns you
can specify, the data type of the
columns, and the existing
constraints on the columns. See
“Restrictions on the Column
Name Variable in the
REFERENCES Clause of ALTER
TABLE” below.
The referenced table can be the Table Name, p. 1-768
same table as the referencing
table, or it can be a different
table in the same database.
Restrictions on the Column Name Variable in the REFERENCES Clause of
ALTER TABLE
Observe the following restrictions on the referenced column (the column or
set of columns that you specify in the column name variable).
Number of Columns
The following restrictions apply to the number of columns that you can
specify in the column name variable:
1-58
■
The number of referenced columns in the referenced table must
match the number of referencing columns in the referencing table.
■
If you are using the REFERENCES clause within the ADD or MODIFY
clauses, you can specify only one column in the column name
variable.
■
If you are using the REFERENCES clause within the ADD
CONSTRAINT clause, you can specify one column or multiple
columns in the column name variable.
Informix Guide to SQL: Syntax
ALTER TABLE
■
The maximum number of columns and the total length of columns
vary with the database server:
❑
If you are using INFORMIX-OnLine Dynamic Server, you can
specify a maximum of 16 column names. The total length of all
the columns cannot exceed 255 bytes.
❑
If you are using INFORMIX-SE, you can specify a maximum of 8
column names. The total length of all the columns cannot exceed
120 bytes.
Data Type of the Column
The data type of each referenced column must be identical to the data type of
the corresponding referencing column. The only exception is that a
referencing column must be INTEGER if the referenced column is SERIAL.
Existing Constraints on the Column
The referenced column or set of columns must be a unique or primary-key
column. That is, the referenced column in the referenced table must already
have a unique or primary-key constraint placed upon it.
Using the REFERENCES Clause in ALTER TABLE
Use the REFERENCES clause to reference a column or set of columns in
another table or the same table. When you are using the ADD or MODIFY
clause, you can reference a single column. When you are using the ADD
CONSTRAINT clause, you can reference a single column or a set of columns.
The table that is referenced in the REFERENCES clause must reside in the same
database as the altered table.
A referential constraint establishes the relationship between columns in two
tables or within the same table. The relationship between the columns is
commonly called a parent-child relationship. For every entry in the child
(referencing) columns, a matching entry must exist in the parent (referenced)
columns.
The referenced column (parent or primary-key) must be a column that is a
unique or primary-key constraint. When you specify a column in the
REFERENCES clause that does not meet this criterion, the database server
returns an error.
SQL Statements 1-59
ALTER TABLE
The referencing column (child or foreign key) that you specify in the Add
Column clause can contain null or duplicate values, but every value (that is,
all foreign-key columns that contain non-null values) in the referencing
columns must match a value in the referenced column.
Relationship Between Referencing and Referenced Columns
A referential constraint has a one-to-one relationship between referencing
and referenced columns. If the primary key is a set of columns, the foreign
key also must be a set of columns that corresponds to the primary key. The
following example creates a new column in the cust_calls table, ref_order.
The ref_order column is a foreign key that references the order_num column
in the orders table.
ALTER TABLE cust_calls ADD
ref_order INTEGER
REFERENCES orders (order_num) BEFORE user_id
When you reference a primary key in another table, you do not have to
explicitly state the primary-key columns in that table. Referenced tables that
do not specify the referenced column default to the primary-key column. In
the previous example, because order_num is the primary key in the orders
table, you do not have to reference that column explicitly.
When you place a referential constraint on a column or set of columns, and a
duplicate or unique index already exists on that column or set of columns, the
index is shared.
The data types of the referencing and referenced column must be identical,
unless the primary-key column is SERIAL data type. When you add a column
that references a SERIAL column, the column that you are adding must be an
INTEGER column.
1-60
Informix Guide to SQL: Syntax
ALTER TABLE
Using the ON DELETE CASCADE Clause
Cascading deletes allow you to specify whether you want rows deleted in the
child table when rows are deleted in the parent table. Normally, you cannot
delete data in the parent table if child tables are associated with it. You can
decide whether you want the rows in the child table deleted with the ON
DELETE CASCADE clause. With the ON DELETE CASCADE clause (or
cascading deletes), when you delete a row in the parent table, any rows that
are associated with that row (foreign keys) in a child table are also deleted.
The principal advantage to the cascading-deletes feature is that it allows you
to reduce the quantity of SQL statements you need to perform delete actions.
For example, the stock table contains the stock_num column as a primary
key. The catalog table refers to the stock_num column as a foreign key. The
following ALTER TABLE statements drop an existing foreign-key constraint
(without cascading delete) and add a new constraint that specifies cascading
deletes:
ALTER TABLE catalog DROP CONSTRAINT aa
ALTER TABLE catalog ADD CONSTRAINT
(FOREIGN KEY (stock_num, manu_code) REFERENCES stock
ON DELETE CASCADE CONSTRAINT ab)
With cascading deletes specified on the child table, in addition to deleting a
stock item from the stock table, the delete cascades to the catalog table that is
associated with the stock_num foreign key. Of course, this cascading delete
works only if the stock_num that you are deleting has not been ordered;
otherwise, the constraint from the items table would disallow the cascading
delete. For more information, see “What Happens to Multiple Child Tables?”
on page 1-62.
You specify cascading deletes with the REFERENCES clause on the ADD
CONSTRAINT clause. You need only the References privilege to indicate
cascading deletes. You do not need the Delete privilege to specify cascading
deletes in tables; however, you do need the Delete privilege on tables that are
referenced in the DELETE statement. After you indicate cascading deletes,
when you delete a row from a parent table, OnLine deletes any associated
matching rows from the child table.
Use the ADD CONSTRAINT clause to add a REFERENCES clause with the ON
DELETE CASCADE clause constraint.
SQL Statements 1-61
ALTER TABLE
What Happens to Multiple Child Tables?
When you have a parent table with two child tables, one with cascading
deletes specified and the other without cascading deletes, and you attempt to
delete a row from the parent table that applies to both child tables, the delete
statement fails, and no rows are deleted from either the parent or child tables.
In the previous example, the stock table is also parent to the items table.
However, you do not need to add the cascading-delete clause to the items
table if you are planning to delete only unordered items. The items table is
used only for ordered items.
Locking and Logging
During deletes, the database server places locks on all qualifying rows of the
referenced and referencing tables. You must turn logging on when you
perform the deletes. When logging is turned off in a database, even temporarily, deletes do not cascade. This restriction applies because you have no
way to roll back actions if logging is turned off . For example, if a parent row
is deleted, and the system crashes before the child rows are deleted, the
database would have dangling child records. Such records would violate
referential integrity. However, when logging is turned back on, subsequent
deletes cascade.
Restriction on Cascading Deletes
Cascading deletes can be used for most deletes except correlated subqueries.
In correlated subqueries, the subquery (or inner SELECT) is correlated when
the value it produces depends on a value produced by the outer SELECT
statement that contains it. If you have implemented cascading deletes, you
cannot write deletes that use a child table in the correlated subquery. You
receive an error when you attempt to delete from a query that contains such
a correlated subquery.
Locks Held During Creation of a Referential Constraint
When you create a referential constraint, an exclusive lock is placed on the
referenced table. The lock is released after you finish with the ALTER TABLE
statement or at the end of a transaction (if you are altering a table in a
database with transactions, and you are using transactions).
1-62
Informix Guide to SQL: Syntax
ALTER TABLE
CHECK Clause
CHECK
Clause
CHECK
(
Condition
p. 1-643
)
A check constraint designates a condition that must be met before data can be
inserted into a column. If a row evaluates to false for any check constraint
that is defined on a table during an insert or update, the database server
returns an error.
Check constraints are defined using search conditions. The search condition
cannot contain the following items: subqueries, aggregates, host variables,
rowids, or stored procedure calls. In addition, the search condition cannot
contain the following functions: the CURRENT, USER, SITENAME,
DBSERVERNAME, or TODAY functions.
Warning: When you specify a date value in a search condition, make sure to specify
4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on how the database server
interprets the search condition. When you specify a 2-digit year, the DBCENTURY
environment variable can affect how the database server interprets the search condition, so the check constraint may not work as you intended. See the “Informix Guide
to SQL: Reference” for more information on the DBCENTURY environment variable.
You cannot create check constraints for columns across tables. When you are
using the ADD or MODIFY clause, the check constraint cannot depend upon
values in other columns of the same table. The following example adds a new
column, unit_price, to the items table and includes a check constraint that
ensures that the entered value is greater than 0:
ALTER TABLE items
ADD (unit_price MONEY (6,2) CHECK (unit_price > 0) )
To create a constraint that checks values in more than one column, use the
ADD CONSTRAINT clause. The following example builds a constraint on the
column that was added in the previous example. The check constraint now
spans two columns in the table.
ALTER TABLE items ADD CONSTRAINT
CHECK (unit_price < total_price)
SQL Statements 1-63
ALTER TABLE
BEFORE Option
Use the BEFORE option of the ADD clause to specify the column before which
a new column or list of columns is to be added. The column that you specify
in the BEFORE option must be an existing column in the table.
If you do not include the BEFORE option in the ADD clause, the database
server adds the new column or list of columns to the end of the table
definition by default.
In the following example, to add the item_weight column before the
total_price column, include the BEFORE option in the ADD clause:
ALTER TABLE items
ADD (item_weight DECIMAL(6,2) NOT NULL
BEFORE total_price)
In the following example, to add the item_weight column to the end of the
table, omit the BEFORE option from the ADD clause:
ALTER TABLE items
ADD (item_weight DECIMAL(6,2) NOT NULL)
DROP Clause
DROP
Clause
DROP
column name
,
(
Element
column name
column name
Purpose
The name of the column that
you want to drop
)
Restrictions
The column must already exist
in the table. If the column is
referenced in a fragment
expression, it cannot be
dropped.
Syntax
Identifier, p. 1-723
Use the DROP clause to drop one or more columns from a table.
1-64
Informix Guide to SQL: Syntax
ALTER TABLE
How Dropping a Column Affects Constraints
When you drop a column, all constraints placed on that column are dropped,
as described in the following list:
■
All single-column constraints are dropped.
■
All referential constraints that reference the column are dropped.
■
All check constraints that reference the column are dropped.
■
If the column is part of a multiple-column unique or primary-key
constraint, the constraints placed on the multiple columns are also
dropped. This action, in turn, triggers the dropping of all referential
constraints that reference the multiple columns.
Because any constraints that are associated with a column are dropped when
the column is dropped, the structure of other tables might also be altered
when you use this clause. For example, if the dropped column is a unique or
primary key that is referenced in other tables, those referential constraints
also are dropped. Therefore the structure of those other tables is also altered.
How Dropping a Column Affects Triggers
When you drop a column that occurs in the triggering column list of an
UPDATE trigger, the column is dropped from the triggering column list. If the
column is the only member of the triggering column list, the trigger is
dropped from the table. See the CREATE TRIGGER statement on page 1-192 for
more information on triggering columns in an UPDATE trigger.
How Dropping a Column Affects Views
When you alter a table by dropping a column, views that depend on the
column are not modified. However, if you attempt to use the view, you
receive an error message indicating that the column was not found.
Views are not dropped because you can change the order of columns in a
table by dropping a column and then adding a new column with the same
name. Views based on that table continue to work. They retain their original
sequence of columns.
SQL Statements 1-65
ALTER TABLE
When you modify a column that has column constraints associated with it,
the following constraints are dropped:
■
All single-column constraints are dropped.
■
All referential constraints that reference the column are dropped.
■
If the modified column is part of a multiple-column unique or
primary-key constraint, all referential constraints that reference the
multiple columns also are dropped.
For example, if you modify a column that has a unique constraint, the unique
constraint is dropped. If this column was referenced by columns in other
tables, those referential constraints are also dropped. In addition, if the
column is part of a multiple-column unique or primary-key constraint, the
multiple-column constraints are not dropped, but any referential constraints
placed on the column by other tables are dropped. For example, a column is
part of a multiple-column primary-key constraint. This primary key is referenced by foreign keys in two other tables. When this column is modified, the
multiple-column primary-key constraint is not dropped, but the referential
constraints placed on it by the two other tables are dropped.
If you modify a column that appears in the triggering column list of an
UPDATE trigger, the trigger is unchanged.
Altering the Next Serial Number
You can use the MODIFY clause to reset the next value of a SERIAL column.
You cannot set the next value below the current maximum value in the
column because that action can cause the database server to generate
duplicate numbers. However, you can set the next value to any value higher
than the current maximum, which creates gaps in the sequence.
Altering the Structure of Tables
When you use the MODIFY clause, you can also alter the structure of other
tables. If the modified column is referenced by other tables, those referential
constraints are dropped. You must add those constraints to the referencing
tables again, using the ALTER TABLE statement.
SQL Statements 1-67
ALTER TABLE
When you change the data type of an existing column, all data is converted
to the new data type, including numbers to characters and characters to
numbers (if the characters represent numbers). The following statement
changes the data type of the quantity column:
ALTER TABLE items MODIFY (quantity CHAR(6))
When a unique or primary-key constraint exists, however, conversion takes
place only if it does not violate the constraint. If a data-type conversion
would result in duplicate values (by changing FLOAT to SMALLFLOAT, for
example, or by truncating CHAR values), the ALTER TABLE statement fails.
Modifying Tables for Null Values
You can modify an existing column that formerly permitted nulls to disallow
nulls, provided that the column contains no null values. To do this, specify
MODIFY with the same column name and data type and the NOT NULL
keywords. The NOT NULL keywords create a not null constraint on the
column.
You can modify an existing column that did not permit nulls to permit nulls.
To do this, specify MODIFY with the column name and the existing data type,
and omit the NOT NULL keywords. The omission of the NOT NULL keywords
drops the not null constraint on the column. However, if a unique index
exists on the column, you can remove it using the DROP INDEX statement.
An alternative method of permitting nulls in an existing column that did not
permit nulls is to use the DROP CONSTRAINT clause to drop the not null
constraint on the column.
Adding a Constraint When Existing Rows Violate the Constraint
If you use the MODIFY clause to add a constraint in the enabled mode and
receive an error message because existing rows would violate the constraint,
you can take the following steps to add the constraint successfully:
1.
Add the constraint in the disabled mode.
Issue the ALTER TABLE statement again, but this time specify the
DISABLED keyword in the MODIFY clause.
2.
1-68
Start a violations and diagnostics table for the target table with the
START VIOLATIONS TABLE statement.
Informix Guide to SQL: Syntax
ALTER TABLE
3.
Issue a SET statement to switch the object mode of the constraint to
the enabled mode.
When you issue this statement, existing rows in the target table that
violate the constraint are duplicated in the violations table; however,
you receive an integrity-violation error message, and the constraint
remains disabled.
4.
Issue a SELECT statement on the violations table to retrieve the
nonconforming rows that are duplicated from the target table.
You might need to join the violations and diagnostics tables to get all
the necessary information.
5.
Take corrective action on the rows in the target table that violate the
constraint.
6.
After you fix all the nonconforming rows in the target table, issue the
SET statement again to switch the disabled constraint to the enabled
mode.
This time the constraint is enabled, and no integrity-violation error
message is returned because all rows in the target table now satisfy
the new constraint.
ADD CONSTRAINT Clause
ADD CONSTRAINT
Clause
Table-Level
Constraint
Definition
p. 1-70
ADD CONSTRAINT
,
(
Table-Level
Constraint
Definition
p. 1-70
)
SQL Statements 1-69
ALTER TABLE
Use the ALTER TABLE statement with the ADD CONSTRAINT keywords to
specify a constraint on a new or existing column or on a set of columns. For
example, to add a unique constraint to the fname and lname columns of the
customer table, use the following statement:
ALTER TABLE customer
ADD CONSTRAINT UNIQUE (lname, fname)
To name the constraint, change the preceding statement, as shown in the
following example:
ALTER TABLE customer
ADD CONSTRAINT UNIQUE (lname, fname) CONSTRAINT u_cust
When you do not provide a constraint name, the database server provides
one. You can find the name of the constraint in the sysconstraints system
catalog table. See Chapter 2 of the Informix Guide to SQL: Reference for more
information about the sysconstraints system catalog table.
Table-Level Constraint Definition
Table-Level
Constraint Definition
,
(
UNIQUE
+
column
name
)
Constraint-Mode
Definitions
p. 1-55
DISTINCT
PRIMARY
KEY
FOREIGN KEY
,
(
column
name
CHECK
Clause
p. 1-63
1-70
+
Informix Guide to SQL: Syntax
)
REFERENCES
Clause
p. 1-57
ALTER TABLE
Element
Purpose
Restrictions
Syntax
column name
The name of the column or
If you are using OnLine, the
Identifier, p. 1-723
columns on which the constraint maximum number of columns is
is placed
16, and the total length of all the
columns cannot exceed
255 bytes. If you are using SE, the
maximum number of columns is
8, and the total length of all the
columns cannot exceed
120 bytes.
Use the Table-Level Constraint Definition option to add a table-level
constraint. You can define a table-level constraint on one column or a set of
columns. You can assign a name to the constraint and set its object mode by
means of the Constraint Mode Definitions option. See “Constraint-Mode
Definitions” on page 1-55 for further information.
Adding a Unique Constraint
You must follow certain rules when you add a unique constraint.
The column or columns can contain only unique values.
When you place a unique constraint on a column or set of columns, and a
unique index already exists on that column or set of columns, the constraint
shares the index. However, if the existing index allows duplicates, the
database server returns an error. You must then drop the existing index
before adding the unique constraint.
When you add a unique constraint, the name of the constraint must be
unique within the database.
ANSI
When you add a unique constraint, the owner.name combination (the combination of the owner name and constraint name) must be unique within the
database. ♦
A composite list can include no more than 16 column names. The total length
of all the columns cannot exceed 255 bytes.
SE
A composite list can include no more than 8 column names, and the total
length of all the columns cannot exceed 120 bytes. ♦
SQL Statements 1-71
ALTER TABLE
Adding a Primary-Key or Unique Constraint
You must follow certain rules when you add a unique or primary-key
constraint.
When you place a unique or primary-key constraint on a column or set of
columns, and a unique index already exists on that column or set of columns,
the constraint shares the index. However, if the existing index allows duplicates, the database server returns an error. You must then drop the existing
index before adding the constraint.
When you place a unique or primary-key constraint on a column or set of
columns, and a referential constraint already exists on that column or set of
columns, the duplicate index is upgraded to unique (if possible) and the
index is shared.
When you place a referential constraint on a column or set of columns, and a
referential constraint already exists on that column or set of columns, the
duplicate index is upgraded to unique (if possible), and the index is shared.
When you add a unique or primary-key constraint, the name of the
constraint must be unique within the database.
ANSI
When you add a unique or primary-key constraint, the owner.name combination (the combination of the owner name and constraint name) must be
unique within the database. ♦
A composite list can include no more than 16 column names. The total length
of all the columns cannot exceed 255 bytes.
Privileges Required for Adding Constraints
When you own the table or have the Alter privilege on the table, you can
create a unique, primary-key, or check constraint on the table and specify
yourself as the owner of the constraint. To add a referential constraint, you
must have the References privilege on either the referenced columns or the
referenced table. When you have the DBA privilege, you can create
constraints for other users.
1-72
Informix Guide to SQL: Syntax
ALTER TABLE
Recovery from Constraint Violations
If you use the ADD CONSTRAINT clause to add a table-level constraint in the
enabled mode and receive an error message because existing rows would
violate the constraint, you can follow a procedure to add the constraint
successfully. See “Adding a Constraint When Existing Rows Violate the
Constraint” on page 1-68.
DROP CONSTRAINT Clause
DROP CONSTRAINT
Clause
Constraint
Name
p. 1-658
DROP CONSTRAINT
,
(
Constraint
Name
p. 1-658
)
Use the DROP CONSTRAINT clause to drop any type of constraint, including
not null constraints.
To drop an existing constraint, specify the DROP CONSTRAINT keywords and
the name of the constraint. The following statement is an example of
dropping a constraint:
ALTER TABLE manufact DROP CONSTRAINT con_name
If a constraint name is not specified when the constraint is created, the
database server generates the name. You can query the sysconstraints system
catalog table for the names (including the owner) of constraints. For example,
to find the name of the constraint placed on the items table, you can issue the
following statement:
SELECT constrname FROM sysconstraints
WHERE tabid = (SELECT tabid FROM systables
WHERE tabname = 'items')
SQL Statements 1-73
ALTER TABLE
When you drop a unique or primary-key constraint that has a corresponding
foreign key, the referential constraints is dropped. For example, if you drop
the primary-key constraint on the order_num column in the orders table and
order_num exists in the items table as a foreign key, that referential
relationship is also dropped.
MODIFY NEXT SIZE Clause
MODIFY NEXT SIZE
Clause
MODIFY NEXT SIZE
Element
kbytes
Purpose
The length in kilobytes that you
want to assign for the next
extent for this table
kbytes
Restrictions
Syntax
The minimum length is four
Expression, p. 1-671
times the disk page size on your
system. For example, if you
have a 2-kilobyte page system,
the minimum length is
8 kilobytes. The maximum
length is equal to the chunk size.
Use the MODIFY NEXT SIZE clause to change the size of new extents. If you
want to specify an extent size of 32 kilobytes, use a statement such as the one
in the following example:
ALTER TABLE customer MODIFY NEXT SIZE 32
The size of existing extents is not changed.
1-74
Informix Guide to SQL: Syntax
ALTER TABLE
LOCK MODE Clause
LOCK MODE
Clause
LOCK MODE
(
PAGE
)
ROW
Use the LOCK MODE keywords to change the locking mode of a table. The
default lock mode is PAGE; it is set if the table is created without using the
LOCK MODE clause. You must use the LOCK MODE clause to change from
page to row locking, as shown in the following example:
ALTER TABLE items LOCK MODE (ROW)
ADD ROWIDS Clause
Tip: Use the ADD ROWIDS clause only on fragmented tables. In nonfragmented
tables, the rowid column remains unchanged. Informix recommends that you use
primary keys as an access method rather than exploiting the rowid column.
By default, fragmented tables do not contain the “hidden” rowid column.
You use the ADD ROWIDS clause to add a new column called rowid for use
with fragmented tables. OnLine assigns a unique number to each row that
remains stable for the life of the row. The database server creates an index that
it uses when search to find the physical location of the row. The ADD ROWIDS
clause cannot be used with other ALTER TABLE commands. After you add the
rowid column, each row contains an additional 4 bytes to store the rowid
value.
For additional information about the rowid column, refer to the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
SQL Statements 1-75
ALTER TABLE
DROP ROWIDS Clause
Use the DROP ROWIDS clause to drop a rowid column only if you created it
with the CREATE TABLE or ALTER FRAGMENT statements on fragmented
tables. You cannot drop the rowid columns of a nonfragmented table. The
DROP ROWIDS clause cannot be used with any other ALTER TABLE
commands.
References
See the CREATE TABLE, DROP TABLE, and LOCK TABLE statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of data-integrity
constraints and the discussion of the ON DELETE CASCADE clause in
Chapter 4. Also see the discussion of creating a database and tables in
Chapter 9.
See the SET statement in this manual for information on object modes.
1-76
Informix Guide to SQL: Syntax
BEGIN WORK
BEGIN WORK
Use the BEGIN WORK statement to start a transaction (a sequence of database
operations that the COMMIT WORK or ROLLBACK WORK statement
terminates).
Syntax
+
BEGIN WORK
Usage
The following code fragment shows how you might place statements within
a transaction:
BEGIN WORK
LOCK TABLE stock
UPDATE stock SET unit_price = unit_price * 1.10
WHERE manu_code = 'KAR'
DELETE FROM stock WHERE description = 'baseball bat'
INSERT INTO manufact (manu_code, manu_name, lead_time)
VALUES ('LYM', 'LYMAN', 14)
COMMIT WORK
Each row that an UPDATE, DELETE, or INSERT statement affects during a
transaction is locked and remains locked throughout the transaction. A transaction that contains many such statements or that contains statements
affecting many rows can exceed the limits that your operating system or the
INFORMIX-OnLine Dynamic Server configuration imposes on the maximum
number of simultaneous locks. If no other user is accessing the table, you can
avoid locking limits and reduce locking overhead by locking the table with
the LOCK TABLE statement after you begin the transaction. Like other locks,
this table lock is released when the transaction terminates.
You can issue the BEGIN WORK statement only if a transaction is not in
progress. If you issue a BEGIN WORK statement while you are in a
transaction, the database server returns an error.
SQL Statements 1-77
BEGIN WORK
ESQL
If you use the BEGIN WORK statement within a routine called by a
WHENEVER statement, specify WHENEVER SQLERROR CONTINUE and
WHENEVER SQLWARNING CONTINUE before the ROLLBACK WORK
statement. These statements prevent the program from looping if the
ROLLBACK WORK statement encounters an error or a warning. ♦
With ANSI-Compliant Databases
ANSI
The BEGIN WORK statement is not needed because transactions are implicit.
A warning is generated if you use a BEGIN WORK statement immediately
after one of the following statements:
■
DATABASE
■
COMMIT WORK
■
CREATE DATABASE
■
ROLLBACK WORK
■
START DATABASE
An error is generated if you use a BEGIN WORK statement after any other
statement. ♦
References
See the COMMIT WORK and ROLLBACK WORK statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of transactions and
locking in Chapter 4 and Chapter 7, respectively.
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Informix Guide to SQL: Syntax
CHECK TABLE
CHECK TABLE
Use the CHECK TABLE statement to compare the data in a table with its
indexes to determine whether they match. Use this statement when you think
a power failure, computer crash, or other program interruption might have
corrupted the data or the indexes. If the CHECK TABLE statement shows that
a table is damaged, use the REPAIR TABLE statement to repair the table.
Syntax
SE
CHECK TABLE
DB
+
Table
Name
p. 1-768
Usage
Specify the name of the database table for which you want to check the data
and associated indexes, as shown in the following example:
CHECK TABLE cust_calls
The CHECK TABLE statement calls the secheck utility. See the INFORMIX-SE
Administrator’s Guide for a full description of the secheck utility.
You must specify a table that is in a database on the current directory. If you
specified a simple name for a database in the DATABASE command, but the
database is not located in the current directory, CHECK TABLE does not search
the DBPATH environment variable to find the directory for the database. The
CHECK TABLE statement will fail. Similarly, if you specified an explicit
pathname for a database in the DATABASE command, but the database is not
located in the current directory, CHECK TABLE does not search for the
database in the directory that you specified. The CHECK TABLE statement
will fail.
SQL Statements 1-79
CHECK TABLE
You cannot use the CHECK TABLE statement on a table unless you own it or
have the DBA privilege.
You cannot use the CHECK TABLE statement on the system catalog table
systables because it is always open. Instead, you can run the secheck utility
from the operating-system prompt. You cannot use the CHECK TABLE
statement on other system catalog tables unless you are user informix.
References
See the REPAIR TABLE statement in this chapter.
In the INFORMIX-SE Administrator’s Guide, see the discussion of the secheck
utility in Chapter 7.
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Informix Guide to SQL: Syntax
CLOSE
CLOSE
Use the CLOSE statement when you no longer need to refer to the rows that
a select or procedure cursor produced or when you want to flush and close
an insert cursor.
Syntax
ESQL
Element
cursor id
CLOSE
Purpose
The name of the cursor to be
closed
cursor id
Restrictions
The DECLARE statement must
have previously declared the
cursor.
Syntax
Identifier, p. 1-723
Usage
Closing a cursor makes the cursor unusable for any statements except OPEN
or FREE and releases resources that the database server had allocated to the
cursor. A CLOSE statement treats a cursor that is associated with an INSERT
statement differently than one that is associated with a SELECT or EXECUTE
PROCEDURE statement.
You can close a cursor that was never opened or that has already been closed.
No action is taken in these cases.
ANSI
You get an error if you close a cursor that was not open. No other action
occurs. ♦
SQL Statements 1-81
CLOSE
Closing a Select or Procedure Cursor
When cursor id is associated with a SELECT or EXECUTE PROCEDURE
statement, closing the cursor terminates the SELECT or EXECUTE
PROCEDURE statement. The database server releases all resources that it
might have allocated to the active set of rows, for example, a temporary table
that it used to hold an ordered set. The database server also releases any locks
that it might have held on rows that were selected through the cursor. If a
transaction contains the CLOSE statement, the database server does not
release the locks until you execute COMMIT WORK or ROLLBACK WORK.
After you close a select or procedure cursor, you cannot execute a FETCH
statement that names that cursor until you have reopened it.
Closing an Insert Cursor
When cursor id is associated with an INSERT statement, the CLOSE statement
writes any remaining buffered rows into the database. The number of rows
that were successfully inserted into the database is returned in the third
element of the sqlerrd array in the sqlca structure (see the SQL API productspecific name in the following chart). For information on using SQLERRD to
count the total number of rows that were inserted, see the PUT statement on
page 1-416.
1-82
Product
Field Name
ESQL/C
sqlca.sqlerrd[2]
ESQL/COBOL
SQLERRD(3) OF SQLCA
Informix Guide to SQL: Syntax
CLOSE
The SQLCODE field of the sqlca structure indicates the result of the CLOSE
statement for an insert cursor. If all buffered rows are successfully inserted,
SQLCODE is set to zero. If an error is encountered, SQLCODE is set to a
negative error message number. See the following chart for the field name for
each SQL API product.
Product
Field Name
ESQL/C
sqlca.sqlcode
ESQL/COBOL
SQLCODE OF SQLCA
When SQLCODE is zero, the row buffer space is released, and the cursor is
closed; that is, you cannot execute a PUT or FLUSH statement that names the
cursor until you reopen it.
Tip: When you encounter an SQLCODE error, a corresponding SQLSTATE error
value might exist. Check the GET DIAGNOSTICS statement for information about
how to get the SQLSTATE value and how to use the GET DIAGNOSTICS statement to
interpret the SQLSTATE value.
If the insert is not successful, the number of successfully inserted rows is
stored in sqlerrd. Any buffered rows that follow the last successfully inserted
row are discarded. Because the CLOSE statement failed in this case, the cursor
is not closed. A second CLOSE statement can be successful because no
buffered rows exist. A subsequent OPEN statement should also be successful
because the OPEN statement performs a successful implicit close. For
example, a CLOSE statement can fail if insufficient disk space prevents some
of the rows from being inserted.
SQL Statements 1-83
CLOSE
Using End of Transaction to Close a Cursor
The COMMIT WORK and ROLLBACK WORK statements close all cursors
except those that are declared with hold. It is better to close all cursors
explicitly, however. For select or procedure cursors, this action simply makes
the intent of the program clear. It also helps to avoid a logic error if the WITH
HOLD clause is later added to the declaration of a cursor.
For an insert cursor, it is important to use the CLOSE statement explicitly so
that you can test the error code. Following the COMMIT WORK statement,
SQLCODE reflects the result of the COMMIT statement, not the result of
closing cursors. If you use a COMMIT WORK statement without first using a
CLOSE statement, and if an error occurs while the last buffered rows are being
written to the database, the transaction is still committed.
For the use of insert cursors and the WITH HOLD clause, see the DECLARE
statement on page 1-234.
References
See the DECLARE, FETCH, FLUSH, FREE, OPEN, and PUT statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of cursors in
Chapter 5.
1-84
Informix Guide to SQL: Syntax
CLOSE DATABASE
CLOSE DATABASE
Use the CLOSE DATABASE statement to close the current database.
Syntax
+
CLOSE DATABASE
Usage
Following the CLOSE DATABASE statement, the only legal SQL statements are
CREATE DATABASE, DATABASE, and DROP DATABASE. A DISCONNECT
statement can also follow a CLOSE DATABASE statement, but only if an
explicit connection existed before you issue the CLOSE DATABASE statement.
A CONNECT statement can follow a CLOSE DATABASE statement without
any restrictions.
SE
You can also use the START DATABASE and ROLLFORWARD DATABASE
statements after CLOSE DATABASE. ♦
Issue the CLOSE DATABASE statement before you drop the current database.
If your database has transactions, and if you have started a transaction, you
must issue a COMMIT WORK statement before you use the CLOSE DATABASE
statement.
The following example shows how to use the CLOSE DATABASE statement to
drop the current database:
DATABASE stores7
.
.
.
CLOSE DATABASE
DROP DATABASE stores7
SQL Statements 1-85
CLOSE DATABASE
ESQL
The CLOSE DATABASE statement cannot appear in a multistatement PREPARE
operation.
If you use the CLOSE DATABASE statement within a routine called by a
WHENEVER statement, specify WHENEVER SQLERROR CONTINUE and
WHENEVER SQLWARNING CONTINUE before the ROLLBACK WORK
statement. This action prevents the program from looping if the ROLLBACK
WORK statement encounters an error or a warning.
When you issue the CLOSE DATABASE statement, declared cursors are no
longer valid. You must redeclare any cursors that you want to use. ♦
References
See the CONNECT, CREATE DATABASE, DATABASE, DISCONNECT, and DROP
DATABASE statements in this manual.
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Informix Guide to SQL: Syntax
COMMIT WORK
COMMIT WORK
Use the COMMIT WORK statement to commit all modifications made to the
database from the beginning of a transaction.
Syntax
COMMIT WORK
Usage
Use the COMMIT WORK statement when you are sure you want to keep
changes that are made to the database from the beginning of a transaction.
Use the COMMIT WORK statement only at the end of a multistatement
operation.
The COMMIT WORK statement releases all row and table locks.
ESQL
The COMMIT WORK statement closes all open cursors except those declared
with hold. ♦
Issuing COMMIT WORK in a Database That Is Not ANSI Compliant
In a database that is not ANSI compliant, you must issue a COMMIT WORK
statement at the end of a transaction if you initiated the transaction with a
BEGIN WORK statement. If you fail to issue a COMMIT WORK statement in
this case, the database server rolls back the modifications to the database that
the transaction made.
If you are using a database that is not ANSI compliant, and you do not issue
a BEGIN WORK statement, the database server executes each statement
within its own transaction. These single-statement transactions do not
require either a BEGIN WORK statement or a COMMIT WORK statement.
SQL Statements 1-87
COMMIT WORK
Issuing COMMIT WORK in an ANSI-Compliant Database
ANSI
In an ANSI-compliant database, you do not need to mark the beginning of a
transaction. An implicit transaction is always in effect. You only need to mark
the end of each transaction. A new transaction starts automatically after each
COMMIT WORK or ROLLBACK WORK statement.
You must issue an explicit COMMIT WORK statement to mark the end of each
transaction. If you fail to do so, the database server rolls back the modifications to the database that the transaction made. ♦
References
See the BEGIN WORK, ROLLBACK WORK, and DECLARE statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of transactions in
Chapter 4.
1-88
Informix Guide to SQL: Syntax
CONNECT
CONNECT
Use the CONNECT statement to connect to a database environment.
Syntax
+
CONNECT TO
Database
Environment
p. 1-94
ESQL
ESQL
AS
AS
' connection
name '
conn_nm
variable
USER
Clause
p. 1-99
DEFAULT
ESQL
WITH CONCURRENT TRANSACTION
Element
connection
name
Purpose
Quoted string that assigns a
name to the connection
conn_nm
variable
Host variable that holds the
value of connection name
Restrictions
If your application makes
multiple connections to the same
database environment, you must
specify a unique connection
name for each connection.
Variable must be a fixed-length
character data type.
Syntax
Quoted String,
p. 1-757
Variable name must
conform to
language-specific
rules for variable
names.
SQL Statements 1-89
CONNECT
Usage
The CONNECT statement connects an application to a database environment.
The database environment can be a database, a database server, or a database
and a database server. If the application successfully connects to the specified
database environment, the connection becomes the current connection for
the application. SQL statements fail if no current connection exists between an
application and a database server. If you specify a database name, the
database server opens the database.You cannot use the CONNECT statement
in a PREPARE statement.
An application can connect to several database environments at the same
time, and it can establish multiple connections to the same database
environment, provided each connection has a unique connection name. The
only restriction on this is that an application can establish only one
connection to each local server that uses the shared-memory connection
mechanism. To find out whether a local server uses the shared memory
connection mechanism or the local loopback connection mechanism,
examine the $INFORMIXDIR/etc/sqlhosts file. (See the INFORMIX-OnLine
Dynamic Server Administrator’s Guide for more information.)
Only one connection is current at any time; other connections are dormant.
The application cannot interact with a database through a dormant
connection. When an application establishes a new connection, that
connection becomes current, and the previous current transaction becomes
dormant. You can make a dormant connection current with the SET
CONNECTION statement. See “SET CONNECTION” on page 1-527.
Privileges for Executing the CONNECT Statement
The current user, or PUBLIC, must have the Connect database privilege on the
database specified in the CONNECT statement.
The user who executes the CONNECT statement cannot have the same user
name as an existing role in the database.
For information on using the USER clause to specify an alternate user name
when the CONNECT statement connects to a database server on a remote
host, see “USER Clause” on page 1-99.
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Informix Guide to SQL: Syntax
CONNECT
Connection Identifiers
The optional connection name is a unique identifier that an application can use
to refer to a connection in subsequent SET CONNECTION and DISCONNECT
statements. If the application does not provide connection name (or a conn_nm
host variable), it can refer to the connection using the database environment.
If the application makes more than one connection to the same database
environment, however, each connection must have a unique connection
name.
After you associate a connection name with a connection, you can refer to the
connection using only that connection name.
The value of connection name is case sensitive.
Connection Context
Each connection encompasses a set of information that is called the connection
context. The connection context includes the name of the current user, the
information that the database environment associates with this name, and
information on the state of the connection (such as whether an active transaction is associated with the connection). The connection context is saved
when an application becomes dormant, and this context is restored when the
application becomes current again. (For more information on dormant
connections, see “Making a Dormant Connection the Current Connection”
on page 1-528.)
The DEFAULT Option
Use the DEFAULT option to request a connection to a default database server,
called a default connection. The default database server can be either an
INFORMIX-OnLine Dynamic Server or a INFORMIX-SE database server, and it
can be local or remote. To designate the default database server, set its name
in the environment variable INFORMIXSERVER. This form of the CONNECT
statement does not open a database.
If you select the DEFAULT option for the CONNECT statement, you must use
the DATABASE statement, the CREATE DATABASE statement, or the START
DATABASE statement to open or create a database in the default database
environment.
SQL Statements 1-91
CONNECT
The Implicit Connection with DATABASE Statements
If you do not execute a CONNECT statement in your application, the first SQL
statement must be one of the following database statements (or a single
statement PREPARE for one of the following statements):
■
DATABASE
■
CREATE DATABASE
■
START DATABASE
■
DROP DATABASE
If one of these database statements is the first SQL statement in an application,
the statement establishes a connection to a server, which is known as an
implicit connection. If the database statement specifies only a database name,
the database server name is obtained from the DBPATH environment
variable. This situation is described in “Locating the Database” on page 1-97.
An application that makes an implicit connection can establish other
connections explicitly (using the CONNECT statement) but cannot establish
another implicit connection unless the original implicit connection is disconnected. An application can terminate an implicit connection using the
DISCONNECT statement.
After any implicit connection is made, that connection is considered to be the
default connection, regardless of whether the server is the default specified
by the INFORMIXSERVER environment variable. This default allows the
application to refer to the implicit connection if additional explicit connections are made, because the implicit connection does not have an identifier.
For example, if you establish an implicit connection followed by an explicit
connection, you can make the implicit connection current by issuing the SET
CONNECTION DEFAULT statement. This means, however, that once you
establish an implicit connection, you cannot use the CONNECT DEFAULT
command because the implicit connection is considered to be the default
connection.
The database statements can always be used to open a database or create a
new database on the current database server.
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CONNECT
The WITH CONCURRENT TRANSACTION Option
The WITH CONCURRENT TRANSACTION clause lets you switch to a different
connection while a transaction is active in the current connection. If the
current connection was not established using the WITH CONCURRENT
TRANSACTION clause, you cannot switch to a different connection if a transaction is active; the CONNECT or SET CONNECTION statement fails, returning
an error, and the transaction in the current connection continues to be active.
In this case, the application must commit or roll back the active transaction in
the current connection before it switches to a different connection.
The WITH CONCURRENT TRANSACTION clause supports the concept of
multiple concurrent transactions, where each connection can have its own
transaction and the COMMIT WORK and ROLLBACK WORK statements affect
only the current connection.The WITH CONCURRENT TRANSACTION clause
does not support global transactions in which a single transaction spans
databases over multiple connections. The COMMIT WORK and ROLLBACK
WORK statements do not act on databases across multiple connections.
The following example illustrates how to use the WITH CONCURRRENT
TRANSACTION clause:
main()
{
EXEC SQL connect to 'a@srv1' as 'A';
EXEC SQL connect to 'b@srv2' as 'B' with concurrent transaction;
EXEC SQL connect to 'c@srv3' as 'C' with concurrent transaction;
/*
Execute SQL statements in connection 'C' , starting a
transaction
*/
EXEC SQL set connection 'B'; -- switch to connection 'B'
/*
Execute SQL statements starting a transaction in 'B'.
Now there are two active transactions, one each in 'B'
and 'C'.
*/
EXEC SQL set connection 'A'; -- switch to connection 'A'
/*
Execute SQL statements starting a transaction in 'A'.
Now there are three active transactions, one each in 'A',
'B' and 'C'.
*/
EXEC SQL set connection 'C'; -- ERROR, transaction active in 'A'
SQL Statements 1-93
CONNECT
/*
SET CONNECTION 'C' fails (current connection is still 'A')
The transaction in 'A' must be committed/rolled back since
connection 'A' was started without the CONCURRENT TRANSACTION
clause.
*/
EXEC SQL commit work;-- commit tx in current connection ('A')
/*
Now, there are two active transactions, in 'B' and in 'C',
which must be committed/rolled back separately
*/
EXEC SQL set connection 'B'; -- switch to connection 'B'
EXEC SQL commit work;
-- commit tx in current connection ('B')
EXEC SQL set connection 'C'; -- go back to connection 'C'
EXEC SQL commit work;
-- commit tx in current connection ('C')
EXEC SQL disconnect all;
}
Warning: When an application uses the WITH CONCURRENT TRANSACTION
clause to establish multiple connections to the same database environment, a deadlock
condition can occur. A deadlock condition occurs when one transaction obtains a lock
on a table, and a concurrent transaction tries to obtain a lock on the same table,
resulting in the application waiting for itself to release the lock.
Database Environment
Database
Environment
'dbname'
'@dbservername'
'dbname@dbservername'
ESQL
db_env variable
SE
'pathname/dbname'
'pathname/dbname@dbservername'
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Informix Guide to SQL: Syntax
CONNECT
Element
Purpose
db_env variable Host variable that contains a
value representing a database
environment
dbname
Quoted string that identifies the
name of the database to which a
connection is made
dbservername
Quoted string that identifies the
name of the database server to
which a connection is made
dbname@
dbservername
Quoted string that identifies the
name of the database and
database server to which a
connection is made
Restrictions
Variable must be a fixed-length
character data type. The value
stored in this host variable must
have one of the databaseenvironment formats listed in
the syntax diagram.
Specified database must already
exist. If you previously set the
DELIMIDENT environment
variable, surrounding quotes
must be single. If the
DELIMIDENT environment
variable has not been previously
set, surrounding quotes can be
single or double.
Specified database server must
match the name of a server in the
sqlhosts file. If you previously
set the DELIMIDENT
environment variable,
surrounding quotes must be
single. If the DELIMIDENT
environment variable has not
been previously set,
surrounding quotes can be
single or double.
Specified database must already
exist. Specified database server
must match the name of a server
in the sqlhosts file. If you
previously set the DELIMIDENT
environment variable,
surrounding quotes must be
single. If the DELIMIDENT
environment variable has not
been previously set,
surrounding quotes can be
single or double.
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
Quoted String,
p. 1-757
Quoted String,
p. 1-757
Quoted String,
p. 1-757
(1 of 2)
SQL Statements 1-95
CONNECT
Element
pathname/
dbname
pathname/
dbname@
dbservername
Purpose
Quoted string that identifies the
path of the database directory up
to the parent directory of the
.dbs directory (the directory
where INFORMIX-SE database
files reside). See “Locating the
Database” on page 1-97 for the
default actions taken by the
database server if you omit the
pathname.
Quoted string that identifies the
path of the database directory up
to the parent directory of the
.dbs directory (the directory
where INFORMIX-SE database
files reside). The string also
specifies the name of the
INFORMIX-SE database server.
See “Locating the Database” on
page 1-97 for the default actions
taken by the database server if
you omit the pathname.
Restrictions
Specified path must exist on the
computer where the database
server resides. Specified
database must already exist.
Syntax
Quoted String,
p. 1-757. Pathname
must conform to the
rules of your
operating system.
Specified path must exist on the
computer where the database
server resides. Specified
database server must match the
name of a server in the sqlhosts
file. Specified database must
already exist.
Quoted String
p. 1-757. Pathname
must conform to the
rules of your
operating system.
(2 of 2)
Specifying the Database Environment
Using the options shown in the syntax diagram, you can specify either a
server and a database, a database server only, or a database only.
Specifying a Database Server Only
The @dbservername option establishes a connection to the named database
server only; it does not open a database. When you use this option, you must
subsequently use the DATABASE, CREATE DATABASE, or START DATABASE
statement (or a PREPARE statement for one of these statements and an
EXECUTE statement) to open a database.
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CONNECT
Specifying a Database Only
The dbname option (for OnLine or SE) and the pathname/dbname option (for SE
only) establish connections to the default server or to another database server
in the DBPATH variable. It also locates and opens the named database.The
same is true of the db_env variable option if it specifies only a database name.
See “Locating the Database” below for the order in which an application
connects to different database servers to locate a database.
Locating the Database
How a database is located and opened depends on both of the following
factors:
■
Whether you specify a database server name in the database
environment expression
■
Whether the database server is INFORMIX-OnLine Dynamic Server or
INFORMIX-SE
Database Server and Database Specified
If you specify both a database server and a database in the CONNECT
statement, your application connects to the database server, which locates
and opens the database. If it is an OnLine database server, it uses parameters
that are specified in the ONCONFIG configuration file to locate the database.
SE
The SE database server searches the directory that you supply. If you do not
supply a directory path, it searches in the current directory (if the database
server is local), the login directory (if the database server is remote), or the
DBPATH environment variable. ♦
If the database server that you specify is not on-line, you get an error.
SQL Statements 1-97
CONNECT
Only Database Specified
If you specify only a database in your CONNECT statement, not a database
server, the application obtains the name of a database server from the
DBPATH environment variable. The database server in the
INFORMIXSERVER environment variable is always added in front of the
DBPATH value specified by the user. Set environment variables as the
following example shows:
setenv INFORMIXSERVER srvA
setenv DBPATH //srvB://srvC
The resulting DBPATH used by your application is shown in the following
example:
//srvA://srvB://srvC
The application first establishes a connection to the database server specified
by INFORMIXSERVER. If it is an OnLine database server, it uses parameters
that are specified in the configuration file to locate the database.
If the database does not reside on the default database server, or if the default
database server is not on-line, the application connects to the next database
server in DBPATH. In the previous example, this server would be srvB.
SE
An SE database server searches the directory that you supply. If you do not
supply a directory path, it searches in the current directory if the database
server is local or the login directory if the database server is remote.
If a database server in DBPATH is an SE database server, it can contain a
directory path. For example, the DBPATH might be as follows:
//srvB://srvC/usr/xyz
The database server will search for the database in the /usr/xyz directory. If
an SE server in DBPATH does not have any directory path specified, the
database server searches in the current directory if the database server is local
or in the remote directory if the database server is remote. ♦
If a directory in DBPATH is an NFS-mounted directory, it is expanded to
contain the host name of the NFS computer and the complete pathname of the
directory on the NFS host. In this case, the host name must be listed in your
sqlhosts file as a dbservername, and an sqlexecd daemon must be running
on the NFS host.
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CONNECT
USER Clause
USER
Clause
USER
' user identifier '
USING
auth variable
user_id
variable
Element
auth variable
Purpose
Host variable that holds the
valid password for the login
name specified in user identifier
or user_id variable
user_id variable The name of an ESQL/C or
ESQL/COBOL host variable that
holds the value of user identifier
user identifier
Quoted string that is a valid
login name for the application
Restrictions
Variable must be a fixed-length
character data type. The
password stored in this variable
must exist in the /etc/passwd
file. If the application connects to
a remote database server, the
password must exist in this file
on both the local and remote
database servers.
Variable must be a fixed-length
character data type. The login
name stored in this variable is
subject to the same restrictions
as the user identifier variable.
Specified login name must exist
in the /etc/passwd file. If the
application connects to a remote
server, the login name must exist
in this file on both the local and
remote database servers.
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
Variable name must
conform to
language-specific
rules for variable
names.
Quoted String,
p. 1-757
The User clause specifies information that is used to determine whether the
application can access the target computer when the CONNECT statement
connects to the database server on a remote host. Subsequent to the
CONNECT statement, all database operations on the remote host use the
specified user name.
SQL Statements 1-99
CONNECT
The connection is rejected if the following conditions occur:
ESQL
X/O
■
The specified user lacks the privileges to access the database named
in the database environment.
■
The specified user does not have the required permissions to connect
to the remote host.
■
You supply a USER clause but do not include the USING auth variable
phrase.
In compliance with the X/Open specification for the CONNECT statement, the
ESQL/C and ESQL/COBOL preprocessors allow a CONNECT statement that
has a USER clause without the USING auth variable phrase. The connection is
rejected at runtime by Informix database servers, however, if the auth variable
is not present. ♦
If you do not supply the USER clause, the connection is attempted using the
default user ID. The default Informix user ID is the login name of the user
running the application. In this case, network permissions are obtained using
the standard UNIX authorization procedures (for example, checking the
/etc/hosts.equiv file).
Connecting to pre-6.0 INFORMIX-OnLine Dynamic Servers
The CONNECT statement syntax described in this chapter is valid for a
Version 6.0 or later application connecting to pre-Version 6.0 database
servers. As with Version 6.0 or later database servers, an implicit connection
can be made to a pre-Version 6.0 server, provided that no existing implicit
connections exist and no implicit connections have been previously
terminated.
SE
1-100
You cannot connect to a pre-Version 6.0 server from a Version 6.0 or later
application if the INFORMIX-SE database server has a nettype seipcpip. ♦
Informix Guide to SQL: Syntax
CONNECT
Connections to pre-Version 6.0 OnLine database server differ from
connections to Version 6.0 and later database servers in the following
respects:
■
The CLOSE DATABASE statement causes a connection to a preVersion 6.0 database server to be dropped. The same statement,
applied to a connection to a Version 6.0 or later database server,
causes the database to close, but the connection remains.
■
If an application makes a connection to a pre-Version 6.0 database
server without using the WITH CONCURRENT TRANSACTION
clause, you must close the database (effectively dropping the
connection) before switching to a different connection; otherwise,
OnLine returns error -1800.
References
See the DISCONNECT, SET CONNECTION, DATABASE, START DATABASE, and
CREATE DATABASE statements in this manual.
For information on the contents of the sqlhosts file, refer to the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
SQL Statements 1-101
CREATE AUDIT
CREATE AUDIT
Use the CREATE AUDIT statement to create an audit-trail file and to start
writing the audit trail for an INFORMIX-SE database.
Syntax
SE
+
CREATE AUDIT FOR
Table
Name
p. 1-768
IN
' pathname '
Synonym
Name
p. 1-766
Element
pathname
Purpose
The full operating-system
pathname and filename for the
audit-trail file
Restrictions
You can specify only one
audit-trail file for a table. If an
audit-trail file already exists for
the table, the statement is not
executed.
Syntax
The pathname and
filename must
conform to the
conventions of your
operating system.
Usage
You can create an audit trail to keep a record of all modifications to a table.
An audit trail is a complete history of all additions, deletions, and updates to
the table. You can use the audit trail to reconstruct the table from a backup
copy that is made when the audit trail is created.
You can use the CREATE AUDIT statement only with INFORMIX-SE.
INFORMIX-OnLine Dynamic Server uses log files to provide full database
logging.
To use the CREATE AUDIT statement, you must own the table or have the DBA
privilege. You must set the Execute privilege for all directories below root in
pathname for each class of user (owner, group, and public) that accesses your
database.
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Informix Guide to SQL: Syntax
CREATE AUDIT
If an audit-trail file with the same pathname already exists, the CREATE
AUDIT statement does nothing. If an audit-trail file for the same table exists
with a different pathname, an error message is returned.
Make a backup copy of your database files as soon as you run the CREATE
AUDIT statement but before you make any further changes to the database.
(See the RECOVER TABLE statement for an example.) If possible, put the audit
trail file on a different physical device from the one that holds your data so
that a failure of one does not damage the data on the other.
Audit trails slow your access to the database very slightly; each alteration of
the database is recorded in the audit trail file as well as in the database files.
The following example shows how to use the CREATE AUDIT statement in a
UNIX environment:
CREATE AUDIT FOR orders IN '/u/safe/orders.aud'
References
See the DROP AUDIT and RECOVER TABLE statements in this manual.
For more information on audit trails, see the INFORMIX-SE Administrator’s
Guide.
SQL Statements 1-103
CREATE DATABASE
CREATE DATABASE
Use the CREATE DATABASE statement to create a new database.
Syntax
+
CREATE
DATABASE
Database
Name
p. 1-660
OL
IN
dbspace
SE
SE Log Clause
OL
OL Log Clause
SE Log Clause
WITH LOG IN ' pathname '
MODE ANSI
OL Log Clause
WITH
LOG
BUFFERED
LOG MODE ANSI
Element
dbspace
pathname
1-104
Purpose
The name of the dbspace where
you want to store the data for
this database; default is the root
dbspace
The full pathname, including the
file name, for the log file
Informix Guide to SQL: Syntax
Restrictions
Syntax
The dbspace must already exist. Identifier, p. 1-723
You cannot specify an existing
file.
The pathname and
filename must
conform to the
conventions of your
operating system.
CREATE DATABASE
Usage
The database that you create becomes the current database.
The database name that you use must be unique within the
INFORMIX-OnLine Dynamic Server environment in which you are working.
OnLine creates the system catalog tables that contain the data dictionary,
which describes the structure of the database in the dbspace. If you do not
specify the dbspace, OnLine creates the system catalog tables in the root
dbspace.
When you create a database, you alone have access to it. The database
remains inaccessible to other users until you, as DBA, grant database privileges. For information on granting database privileges, see the GRANT
statement on page 1-340.
The following statement creates the vehicles database in the root dbspace:
CREATE DATABASE vehicles
The following statement creates the vehicles database in the research
dbspace:
CREATE DATABASE vehicles IN research
SE
The following example creates the vehicles database in your current
directory:
CREATE DATABASE vehicles
The data for the database is placed in a subdirectory of your current directory
with the name database-name.dbs. The system catalog, tables, data, and index
files are placed in this directory, except for tables that you explicitly instruct
be placed elsewhere (see the CREATE TABLE statement on page 1-154). The
rules for directory names on your operating system govern the length of the
name that you choose for the database. ♦
ESQL
In SQL APIs, the CREATE DATABASE statement cannot appear in a
multistatement PREPARE operation. ♦
SQL Statements 1-105
CREATE DATABASE
ANSI-Compliant Databases
ANSI
You have the option of creating an ANSI-compliant database.
ANSI-compliant databases are set apart from databases that are not ANSI-
compliant by the following features:
■
All statements are automatically contained in transactions. All
databases on the INFORMIX-OnLine Dynamic Server use unbuffered
logging.
■
Owner-naming is enforced. You must use the owner name when
referring to each table, view, synonym, index, or constraint unless
you are the owner.
■
For databases on an OnLine database server, the default isolation
level available is repeatable read.
■
Default privileges on objects differ from those in databases that are
not ANSI-compliant. Users do not receive PUBLIC privilege to tables
and synonyms by default.
Other slight differences exist between databases that are ANSI-compliant and
those that are not. These differences are noted as appropriate with the related
<vk>SQL statement. ♦
Logging on INFORMIX-OnLine Dynamic Server
In the event of a failure, INFORMIX-OnLine Dynamic Server uses the log to recreate all committed transactions in your database.
If you do not specify the WITH LOG statement, you cannot use transactions
or the statements that are associated with databases that have logging (BEGIN
WORK, COMMIT WORK, ROLLBACK WORK, SET LOG, and SET ISOLATION).
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CREATE DATABASE
Designating Buffered Logging
The following example creates a database that uses a buffered log:
CREATE DATABASE vehicles WITH BUFFERED LOG
If you use a buffered log, you marginally enhance the performance of logging
at the risk of not being able to re-create the last few transactions after a failure.
(See the discussion of buffered logging in Chapter 9 of the Informix Guide to
SQL: Tutorial.)
ANSI
An ANSI-compliant database does not use buffered logging. ♦
Designating an ANSI-Compliant INFORMIX-OnLine Dynamic Server
Database
The following example creates an ANSI-compliant database:
CREATE DATABASE employees WITH LOG MODE ANSI
Creating an ANSI-compliant database does not mean that you get ANSI
warnings when you run the database. You must use the -ansi flag or the
DBANSIWARN environment variable to receive warnings.
For additional information about -ansi and DBANSIWARN, see Chapter 4 in
the Informix Guide to SQL: Tutorial.
Logging on INFORMIX-SE
SE
The following example creates an INFORMIX-SE database named accounts
with a log file. You can use the full pathname and filename to designate the
log file. If you specify a filename only, the log file is created in the current
working directory.
CREATE DATABASE accounts WITH LOG IN '/acct/f1993/acct_log'
If you specify the WITH LOG IN keywords, you can use transactions and the
statements that are associated with transactions (BEGIN WORK, COMMIT
WORK, and ROLLBACK WORK). Conversely, if you do not specify the WITH
LOG IN keywords, you cannot use transactions.
SQL Statements 1-107
CREATE DATABASE
You can use the START DATABASE statement to assign a log file to an existing
INFORMIX-SE database or to assign a new log file with a different name.
You can run the following SELECT statement to determine the location of the
log file for the current database:
SELECT dirpath FROM informix.systables
WHERE tabtype = 'L'
Designating an ANSI-Compliant INFORMIX-SE Database
The following example creates an ANSI-compliant database:
CREATE DATABASE employees WITH LOG IN '/u/acctg/lfile' MODE ANSI
♦
References
See the CLOSE DATABASE, CONNECT TO, DATABASE, DROP DATABASE, and
START DATABASE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of creating a database
in Chapter 9.
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Informix Guide to SQL: Syntax
CREATE INDEX
CREATE INDEX
Use the CREATE INDEX statement to create an index for one or more columns
in a table and, optionally, to cluster the physical table in the order of the
index. When more than one column is listed, the concatenation of the set of
columns is treated as a single composite column for indexing. The indexes
can be fragmented into separate dbspaces. You can create a unique or
duplicate index, and you can set the object mode of either type of index.
Syntax
+
CREATE
INDEX
UNIQUE
CLUSTER
Index
Definition
p. 1-111
DISTINCT
OL
OL
FILLFACTOR percent
IN dbspace
FRAGMENT
BY
EXPRESSION
Clause
p. 1-124
Object Modes
for Unique
Indexes
p. 1-128
Object Modes
for Duplicate
Indexes
p. 1-131
Element
Purpose
Restrictions
Syntax
dbspace
The name of the dbspace in
which you want to place the
index
The percentage of each index
page that is filled by index data
when the index is created. The
default value is 90.
The dbspace must exist at the
time you execute the statement.
Identifier, p. 1-723
Value must be in the range 1 to
100.
Literal Number,
p. 1-752
percent
SQL Statements 1-109
CREATE INDEX
Usage
When you issue the CREATE INDEX statement, the table is locked in exclusive
mode. If another process is using the table, the database server cannot
execute the CREATE INDEX statement and returns an error.
SE
You cannot use a ROLLBACK WORK statement to undo a CREATE INDEX
statement. If you roll back a transaction that contains a CREATE INDEX
statement, the index remains, and you do not receive an error message. ♦
UNIQUE Option
The following example creates a unique index:
CREATE UNIQUE INDEX c_num_ix ON customer (customer_num)
A unique index prevents duplicates in the customer_num column. A column
with a unique index can have, at most, one null value. The DISTINCT
keyword is a synonym for the keyword UNIQUE, so the following statement
would accomplish the same task:
CREATE DISTINCT INDEX c_num_ix ON customer (customer_num)
The index in either example is maintained in ascending order, which is the
default order.
If you do not specify the UNIQUE or DISTINCT keywords in a CREATE INDEX
statement, a duplicate index is created. A duplicate index allows duplicate
values in the indexed column.
You can also prevent duplicates in a column or set of columns by creating a
unique constraint with the CREATE TABLE or ALTER TABLE statement. See the
CREATE TABLE or ALTER TABLE statements for more information on creating
unique constraints.
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Informix Guide to SQL: Syntax
CREATE INDEX
How Unique and Referential Constraints Affect Indexes
Internal indexes are created for unique and referential constraints. If a unique
or referential constraint is added after the table is created, the user-created
indexes are used, if appropriate. An appropriate index is one that indexes the
same columns that are used in the referential or unique constraint. If an
appropriate index is not available, a nonfragmented index is created in the
database dbspace.
CLUSTER Option
Use the CLUSTER option to reorder the physical table in the order designated
by the index. The CREATE CLUSTER INDEX statement fails if a CLUSTER index
already exists.
CREATE CLUSTER INDEX c_clust_ix ON customer (zipcode)
This statement creates an index on the customer table that orders the table
physically by zip code.
You cannot create a CLUSTER index on a table that has an audit trail. ♦
SE
If the CLUSTER option is specified in addition to fragments on an index, the
data is clustered only within the context of the fragment and not globally
across the entire table.
Index Definition
Index
Definition
Index
Name
p. 1-741
,
ON
table name
(
)
column name
ASC
Synonym
Name
p. 1-766
DESC
SQL Statements 1-111
CREATE INDEX
Element
Purpose
column name
The name of the column or
You must observe restrictions on Identifier, p. 1-723
columns that you want to index the location of the columns, the
maximum number of columns,
the total width of the columns,
existing constraints on the
columns, and the number of
indexes allowed on the same
columns. See “Restrictions on
the Column Name Variable in
CREATE INDEX” below.
The name of the table on which The table must exist. The table
Identifier, p. 1-723
the index is created
can be a regular database table
or a temporary table.
table name
Restrictions
Syntax
Use the Index Definition portion of the CREATE INDEX statement to give a
name to the index, specify the table on which the index is created, and specify
the column or columns to be used for the index. In addition, the ASC and
DESC keywords allow you to specify whether the index will be sorted in
ascending or descending order.
Restrictions on the Column Name Variable in CREATE INDEX
Observe the following restrictions when you specify the column name
variable:
1-112
■
All the columns you specify must exist and must belong to the same
table.
■
The maximum number of columns and the total width of all columns
vary with the database server. See “Composite Indexes” on
page 1-113.
■
You cannot add an ascending index to a column or column list that
already has a unique constraint on it. See “The ASC and DESC
Keywords” on page 1-113.
■
The number of indexes you can create on the same column or same
sequence of columns is restricted. See “Number of Indexes Allowed”
on page 1-120.
Informix Guide to SQL: Syntax
CREATE INDEX
Composite Indexes
The following example creates a composite index using the stock_num and
manu_code columns of the stock table:
CREATE UNIQUE INDEX st_man_ix ON stock (stock_num, manu_code)
The index prevents any duplicates of a given combination of stock_num and
manu_code. The index is in ascending order by default.
You can include 16 columns in a composite index. The total width of all
indexed columns in a single CREATE INDEX statement cannot exceed
255 bytes.
SE
You can use up to eight columns in a composite index. The total width of all
indexed columns in a single CREATE INDEX statement cannot exceed
120 bytes. ♦
Place columns in the composite index in the order from most frequently used
to least frequently used.
The ASC and DESC Keywords
Use the ASC option to specify an index that is maintained in ascending order.
The ASC option is the default ordering scheme. Use the DESC option to
specify an index that is maintained in descending order. When a column or
list of columns is defined as unique in a CREATE TABLE or ALTER TABLE
statement, the database server implements that UNIQUE CONSTRAINT by
creating a unique ascending index. Thus, you cannot use the CREATE INDEX
statement to add an ascending index to a column or column list that is
already defined as unique.
SQL Statements 1-113
CREATE INDEX
You can create a descending index on such columns, and you can include
such columns in composite ascending indexes in different combinations. For
example, the following sequence of statements is allowed:
CREATE TABLE customer (
customer_num
SERIAL(101) UNIQUE,
fname
CHAR(15),
lname
CHAR(15),
company
CHAR(20),
address1
CHAR(20),
address2
CHAR(20),
city
CHAR(15),
state
CHAR(2),
zipcode
CHAR(5),
phone
CHAR(18)
)
CREATE INDEX cathtmp ON customer (customer_num DESC)
CREATE INDEX c_temp2 ON customer (customer_num, zipcode)
Bidirectional Traversal of Indexes
When you create an index on a column but do not specify the ASC or DESC
keywords, the database server stores the key values in ascending order by
default. If you specify the ASC keyword, the database server stores the key
values in ascending order. If you specify the DESC keyword, the database
server stores the key values in descending order.
Ascending order means that the key values are stored in order from the
smallest key to the largest key. For example, if you create an ascending index
on the lname column of the customer table, last names are stored in the index
in the following order: Albertson, Beatty, Currie.
Descending order means that the key values are stored in order from the
largest key to the smallest key. For example, if you create a descending index
on the lname column of the customer table, last names are stored in the index
in the following order: Currie, Beatty, Albertson.
However, the bidirectional traversal capability of the database server lets you
create just one index on a column and use that index for queries that specify
sorting of results in either ascending or descending order of the sort column.
1-114
Informix Guide to SQL: Syntax
CREATE INDEX
Example of Bidirectional Traversal of an Index
An example can help to illustrate the bidirectional traversal of indexes by the
database server. Suppose that you want to enter the following two queries:
SELECT lname, fname FROM customer ORDER BY lname ASC;
SELECT lname, fname FROM customer ORDER BY lname DESC;
When you specify the ORDER BY clause in SELECT statements such as these,
you can improve the performance of the queries by creating an index on the
ORDER BY column. Because of the bidirectional traversal capability of the
database server, you only need to create a single index on the lname column.
For example, you can create an ascending index on the lname column with
the following statement:
CREATE INDEX lname_bothways ON customer (lname ASC)
The database server will use the ascending index lname_bothways to sort
the results of the first query in ascending order and to sort the results of the
second query in descending order.
In the first query, you want to sort the results in ascending order. So the
database server traverses the pages of the lname_bothways index from left
to right and retrieves key values from the smallest key to the largest key. The
query result is as follows.
lname
fname
Albertson
Frank
Beatty
Lana
Currie
Philip
.
.
.
Vector
Raymond
Wallack
Jason
Watson
George
SQL Statements 1-115
CREATE INDEX
Traversing the index from left to right means that the database server starts
at the leftmost leaf node of the index and continues to the rightmost leaf node
of the index. For an explanation of leaf nodes in indexes, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
In the second query, you want to sort the results in descending order. So the
database server traverses the pages of the lname_bothways index from right
to left and retrieves key values from the largest key to the smallest key. The
query result is as follows.
lname
fname
Watson
George
Wallack
Jason
Vector
Raymond
.
.
.
Currie
Philip
Beatty
Lana
Albertson
Frank
Traversing the index from right to left means that the database server starts
at the rightmost leaf node of the index and continues to the leftmost leaf node
of the index. For an explanation of leaf nodes in indexes, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
1-116
Informix Guide to SQL: Syntax
CREATE INDEX
Choosing an Ascending or Descending Index
In the preceding example, you created an ascending index on the lname
column of the customer table by specifying the ASC keyword in the CREATE
INDEX statement. Then the database server used this index to sort the results
of the first query in ascending order of lname values and to sort the results of
the second query in descending order of lname values. However, you could
have achieved exactly the same results if you had created the index as a
descending index.
For example, the following statement creates a descending index that the
database server can use to process both queries:
CREATE INDEX lname_bothways2 ON customer (lname DESC)
The resulting lname_bothways2 index stores the key values of the lname
column in descending order, from the largest key to the smallest key. When
the database server processes the first query, it traverses the index from right
to left to perform an ascending sort of the results. When the database server
processes the second query, it traverses the index from left to right to perform
a descending sort of the results.
So it does not matter whether you create a single-column index as an
ascending or descending index. Whichever storage order you choose for an
index, the database server can traverse that index in ascending or descending
order when it processes queries.
Use of the ASC and DESC Keywords in Composite Indexes
If you want to place an index on a single column of a table, you do not need
to specify the ASC or DESC keywords because the database server can
traverse the index in either ascending or descending order. The database
server will create the index in ascending order by default, but the server can
traverse this index in either ascending or descending order when it uses the
index in a query.
However, if you create a composite index on a table, the ASC and DESC
keywords might be required. For example, if you want to enter a SELECT
statement whose ORDER BY clause sorts on multiple columns and sorts each
column in a different order, and you want to use an index for this query, you
need to create a composite index that corresponds to the ORDER BY columns.
SQL Statements 1-117
CREATE INDEX
For example, suppose that you want to enter the following query:
SELECT stock_num, manu_code, description, unit_price
FROM stock
ORDER BY manu_code ASC, unit_price DESC
This query sorts first in ascending order by the value of the manu_code
column and then in descending order by the value of the unit_price column.
To use an index for this query, you need to issue a CREATE INDEX statement
that corresponds to the requirements of the ORDER BY clause. For example,
you can enter either of following statements to create the index:
CREATE INDEX stock_idx1 ON stock
(manu_code ASC, unit_price DESC);
CREATE INDEX stock_idx2 ON stock
(manu_code DESC, unit_price ASC);
Now, when you execute the query, the database server uses the index that
you created (either stock_idx1 or stock_idx2) to sort the query results in
ascending order by the value of the manu_code column and then in
descending order by the value of the unit_price column. If you created the
stock_idx1 index, the database server traverses the index from left to right
when it executes the query. If you created the stock_idx2 index, the database
server traverses the index from right to left when it executes the query.
1-118
Informix Guide to SQL: Syntax
CREATE INDEX
Regardless of which index you created, the query result is as follows.
stock_num
manu_code
description
unit_price
8
ANZ
volleyball
$840.00
205
ANZ
3 golf balls
$312.00
110
ANZ
helmet
$244.00
304
ANZ
watch
$170.00
301
ANZ
running shoes
$95.00
310
ANZ
kick board
$84.00
201
ANZ
golf shoes
$75.00
313
ANZ
swim cap
$60.00
6
ANZ
tennis ball
$48.00
9
ANZ
volleyball net
$20.00
5
ANZ
tennis racquet
$19.80
309
HRO
ear drops
$40.00
302
HRO
ice pack
$4.50
113
SHM
18-spd, assmbld
$685.90
1
SMT
baseball gloves
$450.00
6
SMT
tennis ball
$36.00
5
SMT
tennis racquet
$25.00
.
.
.
SQL Statements 1-119
CREATE INDEX
The composite index that was used for this query (stock_idx1 or stock_idx2)
cannot be used for queries in which you specify the same sort direction for
the two columns in the ORDER BY clause. For example, suppose that you
want to enter the following queries:
SELECT stock_num, manu_code, description, unit_price
FROM stock
ORDER BY manu_code ASC, unit_price ASC;
SELECT stock_num, manu_code, description, unit_price
FROM stock
ORDER BY manu_code DESC, unit_price DESC;
If you want to use a composite index to improve the performance of these
queries, you need to enter one of the following CREATE INDEX statements.
You can use either one of the created indexes (stock_idx3 or stock_idx4) to
improve the performance of the preceding queries.
CREATE INDEX stock_idx3 ON stock
(manu_code ASC, unit_price ASC);
CREATE INDEX stock_idx4 ON stock
(manu_code DESC, unit_price DESC);
Number of Indexes Allowed
Restrictions exist on the number of indexes that you can create on the same
column or the same sequence of columns.
Restrictions on the Number of Indexes on a Single Column
You can create only one ascending index and one descending index on a
single column. For example, if you wanted to create all possible indexes on
the stock_num column of the stock table, you could create the following
indexes:
1-120
■
The stock_num_asc index on the stock_num column in ascending
order
■
The stock_num_desc index on the stock_num column in descending
order
Informix Guide to SQL: Syntax
CREATE INDEX
Because of the bidirectional traversal capability of the database server, you
do not need to create both indexes in practice. You only need to create one of
the indexes. Both of these indexes would achieve exactly the same results for
an ascending or descending sort on the stock_num column. For further information on the bidirectional traversal capability of the database server, see
“Bidirectional Traversal of Indexes” on page 1-114.
Restrictions on the Number of Indexes on a Sequence of Columns
You can create multiple indexes on a sequence of columns, provided that
each index has a unique combination of ascending and descending columns.
For example, to create all possible indexes on the stock_num and manu_code
columns of the stock table, you could create the following indexes:
■
The ix1 index on both columns in ascending order
■
The ix2 index on both columns in descending order
■
The ix3 index on stock_num in ascending order and on manu_code
in descending order
■
The ix4 index on stock_num in descending order and on manu_code
in ascending order
Because of the bidirectional-traversal capability of the database server, you
do not need to create these four indexes in practice. You only need to create
two indexes:
■
The ix1 and ix2 indexes achieve exactly the same results for sorts in
which the user specifies the same sort direction (ascending or
descending) for both columns. Therefore, you only need to create
one index of this pair.
■
The ix3 and ix4 indexes achieve exactly the same results for sorts in
which the user specifies different sort directions for the two columns
(ascending on the first column and descending on the second column
or vice versa). Therefore, you only need to create one index of this
pair.
For further information on the bidirectional-traversal capability of the
database server, see “Bidirectional Traversal of Indexes” on page 1-114.
SQL Statements 1-121
CREATE INDEX
FILLFACTOR Clause
Use the FILLFACTOR clause to provide for expansion of the index at a later
date or to create compacted indexes. You provide a percent value ranging
from 1 to 100, inclusive. The default percent value is 90.
When the index is created, OnLine initially fills only that percentage of the
nodes specified with the FILLFACTOR value. If you provide a low percentage
value, such as 50, you allow room for growth in your index. The nodes of the
index initially fill to a certain percentage and contain space for inserts. The
amount of available space depends on the number of keys in each page as
well as the percentage value. For example, with a 50-percent FILLFACTOR
value, the page would be half full and could accommodate doubling in
growth. A low percentage value can result in faster inserts and can be used
for indexes that you expect to grow.
If you provide a high percentage value, such as 99, your indexes are compacted, and any new index inserts result in splitting nodes. The maximum
density is achieved with 100 percent. With a 100-percent FILLFACTOR value,
the index has no room available for growth; any additions to the index result
in splitting the nodes. A 99-percent FILLFACTOR value allows room for at
least one insertion per node. A high percentage value can result in faster
selects and can be used for indexes that you do not expect to grow or for
mostly read-only indexes.
This option takes effect only when you build an index on a table that contains
more than 5,000 rows and uses more than 100 table pages, when you create
an index on a fragmented table, or when you create a fragmented index on a
nonfragmented table. The FILLFACTOR can also be set as a parameter in the
ONCONFIG file. The FILLFACTOR clause on the CREATE INDEX statement
overrides the setting in the ONCONFIG file.
For more information about the ONCONFIG file and the parameters you can
use with ONCONFIG, see the INFORMIX-OnLine Dynamic Server Administrator’s Guide.
1-122
Informix Guide to SQL: Syntax
CREATE INDEX
Attached and Detached Indexes
When you fragment a table and, at a later time, create an index for that table,
the index uses the same fragmentation strategy as the table unless you
specify otherwise with the FRAGMENT BY EXPRESSION clause or the IN
dbspace clause. Any changes to the table fragmentation result in a corresponding change to the index fragmentation. Attached indexes are indexes
created without a fragmentation strategy. Indexes are detached indexes when
they are created with a fragmentation strategy or stored in separate dbspaces
from the table.
For information on the IN dbspace clause, see “The IN dbspace Clause” below.
For information on the FRAGMENT BY EXPRESSION clause, see “The
FRAGMENT BY EXPRESSION Clause” on page 1-124.
The IN dbspace Clause
Use the IN dbspace clause to specify the dbspace where you want your index
to reside. With this clause, you create a detached index, even though the
index is not fragmented. The dbspace that you specify must already exist. If
you do not specify the IN dbspace clause, the index is created in the dbspace
where the table was created. In addition, if you do not specify the IN dbspace
clause, but the underlying table is fragmented, the index is created as a
detached index, subject to all the restrictions on fragmented indexes. See
“The FRAGMENT BY EXPRESSION Clause” on page 1-124 for more
information about fragmented indexes.
The IN dbspace clause allows you to isolate an index. For example, if the
customer table is created in the custdata dbspace, but you want to create an
index in a separate dbspace called custind, use the following statements:
CREATE TABLE customer
.
.
.
IN custdata EXTENT SIZE 16
CREATE INDEX idx_cust ON customer (customer_num)
IN custind
SQL Statements 1-123
CREATE INDEX
The FRAGMENT BY EXPRESSION Clause
FRAGMENT BY
EXPRESSION
Clause
FRAGMENT BY
EXPRESSION
,
frag-expression
IN dbspace
,
frag-expression
IN dbspace
,
Element
dbspace
Purpose
The dbspace that will contain an
index fragment that
frag-expression defines
REMAINDER IN
remainder
dbspace
Restrictions
You must specify at least two
dbspaces. You can specify a
maximum of 2,048 dbspaces.
The dbspaces must exist at the
time you execute the statement.
Syntax
Identifier, p. 1-723
(1 of 2)
1-124
Informix Guide to SQL: Syntax
CREATE INDEX
Element
frag-expression
remainder
dbspace
Purpose
An expression that defines a
fragment where an index key is
to be stored using a range, hash,
or arbitrary rule
Restrictions
If you specify a value for
remainder dbspace, you must
specify at least one fragment
expression. If you do not specify
a value for remainder dbspace, you
must specify at least two
fragment expressions. You can
specify a maximum of 2,048
fragment expressions. Each
fragment expression can contain
only columns from the current
table and only data values from
a single row. The columns
contained in a fragment
expression must be the same as
the indexed columns, or a subset
of the indexed columns. No
subqueries, stored procedures,
current date/time functions, or
aggregates are allowed in a
fragment expression.
The dbspace that contains index If you specify two or more
keys that do not meet the condi- fragment expressions, remainder
tions defined in any fragment
dbspace is optional. If you specify
expression
only one fragment expression,
remainder dbspace is required.
The dbspace specified in
remainder dbspace must exist at
the time you execute the
statement.
Syntax
Expression, p. 1-671,
and Condition,
p. 1-643
Identifier, p. 1-723
(2 of 2)
You use the FRAGMENT BY EXPRESSION clause to define the expressionbased distribution scheme.
SQL Statements 1-125
CREATE INDEX
In an expression-based distribution scheme, each fragment expression in a rule
specifies a dbspace. Each fragment expression within the rule isolates data
and aids the database server in searching for index keys. You can specify one
of the following rules:
■
Range rule
A range rule specifies fragment expressions that use a range to
specify which index keys are placed in a fragment, as the following
example shows:
.
.
.
FRAGMENT BY EXPRESSION
c1 < 100 IN dbsp1,
c1 >= 100 and c1 < 200 IN dbsp2,
c1 >= 200 IN dbsp3;
■
Hash rule
A hash rule specifies fragment expressions that are created when you
use a hash algorithm, which is often implemented with the MOD
function, as the following example shows:
.
.
.
FRAGMENT BY
MOD(id_num,
MOD(id_num,
MOD(id_num,
■
EXPRESSION
3) = 0 IN dbsp1,
3) = 1 IN dbsp2,
3) = 2 IN dbsp3;
Arbitrary rule
An arbitrary rule specifies fragment expressions based on a
predefined SQL expression that typically includes the use of OR
clauses to group data, as the following example shows:
.
.
.
FRAGMENT BY EXPRESSION
zip_num = 95228 OR zip_num = 95443 IN dbsp2,
zip_num = 91120 OR zip_num = 92310 IN dbsp4,
REMAINDER IN dbsp5;
1-126
Informix Guide to SQL: Syntax
CREATE INDEX
Warning: When you specify a date value in a fragment expression, make sure to specify 4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on the distribution scheme. When
you specify a 2-digit year, the DBCENTURY environment variable can affect the distribution scheme and can produce unpredictable results. See the “Informix Guide to
SQL: Reference” for more information on the DBCENTURY environment variable.
Creating Index Fragments
When you fragment a table, all indexes for the table become fragmented the
same as the table, unless you specify a different fragmentation strategy.
Fragmentation of Unique Indexes
You can fragment unique indexes only with a table that uses an expressionbased distribution scheme. The columns referenced in the fragment
expression must be part of the indexed columns. If your CREATE INDEX
statement fails to meet either of these restrictions, the CREATE INDEX fails,
and work is rolled back.
Fragmentation of System Indexes
System indexes (such as those used in referential constraints and unique
constraints) utilize user indexes if they exist. If no user indexes can be
utilized, system indexes remain nonfragmented and are moved to the
dbspace where the database was created. To fragment a system index, create
the fragmented index on the constraint columns, and then add the constraint
using the ALTER TABLE statement.
Fragmentation of Indexes on Temporary Tables
You can create explicit temporary tables with the TEMP TABLE clause of the
CREATE TABLE statement or with the INTO TEMP clause of the SELECT
statement. If you specified more than one dbspace in the DBSPACETEMP
environment variable, but you did not specify an explicit fragmentation
strategy, the database server fragments the temporary table round-robin
across the dbspaces that DBSPACETEMP specifies.
SQL Statements 1-127
CREATE INDEX
If you then try to create a unique index on the temporary table, but you do
not specify a fragmentation strategy for the index, the index is not
fragmented in the same way as the table. You can fragment a unique index
only if the underlying table uses an expression-based distribution scheme,
but the temporary table is fragmented according to a round-robin distribution scheme.
Instead of fragmenting the unique index on the temporary table, the database
server creates the index in the first dbspace that the DBSPACETEMP
environment variable specifies. To avoid this result, use the FRAGMENT BY
EXPRESSION clause to specify a fragmentation strategy for the index.
For more information on the DBSPACETEMP environment variable, see the
Informix Guide to SQL: Reference.
Object Modes for Unique Indexes
Object Modes for
Unique Indexes
DISABLED
ENABLED
FILTERING
WITHOUT
ERROR
WITH
ERROR
1-128
Informix Guide to SQL: Syntax
CREATE INDEX
You can set unique indexes in the following modes: disabled, enabled, and
filtering. The following list explains these modes.
Object Mode
Effect
disabled
A unique index created in disabled mode is not updated after
insert, delete, and update operations that modify the base table.
Because the contents of the disabled index are not up to date, the
optimizer does not use the index during the execution of queries.
enabled
A unique index created in enabled mode is updated after insert,
delete, and update operations that modify the base table. Because
the contents of the enabled index are up to date, the optimizer uses
the index during the execution of queries. If an insert or update
operation causes a duplicate key value to be added to a unique
enabled index, the statement fails.
filtering
A unique index created in filtering mode is updated after insert,
delete, and update operations that modify the base table. Because
the contents of the filtering mode index are up to date, the optimizer
uses the index during the execution of queries. If an insert or update
operation causes a duplicate key value to be added to a unique
index in filtering mode, the statement continues processing, but the
bad row is written to the violations table associated with the base
table. Diagnostic information about the unique-index violation is
written to the diagnostics table associated with the base table.
If you specify filtering mode, you can also specify one of the following error
options.
Error Option
Effect
WITHOUT
ERROR
When a unique-index violation occurs during an insert or update
operation, no integrity-violation error is returned to the user. You
can specify this option only with the filtering-object mode.
WITH ERROR
When a unique-index violation occurs during an insert or update
operation, an integrity-violation error is returned to the user. You
can specify this option only with the filtering-object mode.
SQL Statements 1-129
CREATE INDEX
Specifying Object Modes for Unique Indexes
You must observe the following rules when you specify object modes for
unique indexes in CREATE INDEX statements:
■
You can set a unique index to the enabled, disabled, or filtering
modes.
■
If you do not specify the object mode of a unique index explicitly, the
default mode is enabled.
■
If you do not specify the WITH ERROR or WITHOUT ERROR option for
a filtering-mode unique index, the default error option is WITHOUT
ERROR.
■
When you add a new unique index to an existing base table and
specify the disabled object mode for the index, your CREATE INDEX
statement succeeds even if duplicate values in the indexed column
would cause a unique-index violation.
■
When you add a new unique index to an existing base table and
specify the enabled or filtering-object mode for the index, your
CREATE INDEX statement succeeds provided that no duplicate
values exist in the indexed column that would cause a unique-index
violation. However, if any duplicate values exist in the indexed
column, your CREATE INDEX statement fails and returns an error.
■
When you add a new unique index to an existing base table in the
enabled or filtering mode, and duplicate values exist in the indexed
column, erroneous rows in the base table are not filtered to the violations table. Thus, you cannot use a violations table to detect the
erroneous rows in the base table.
Adding a Unique Index When Duplicate Values Exist in the Column
If you attempt to add a unique index in the enabled mode but receive an error
message because duplicate values are in the indexed column, take the
following steps to add the index successfully:
1-130
1.
Add the index in the disabled mode. Issue the CREATE INDEX
statement again, but this time specify the DISABLED keyword.
2.
Start a violations and diagnostics table for the target table with the
START VIOLATIONS TABLE statement.
Informix Guide to SQL: Syntax
CREATE INDEX
3.
Issue a SET statement to switch the object mode of the index to the
enabled mode. When you issue this statement, existing rows in the
target table that violate the unique-index requirement are duplicated
in the violations table. However, you receive an integrity-violation
error message, and the index remains disabled.
4.
Issue a SELECT statement on the violations table to retrieve the nonconforming rows that are duplicated from the target table. You might
need to join the violations and diagnostics tables to get all the necessary information.
5.
Take corrective action on the rows in the target table that violate the
unique-index requirement.
6.
After you fix all the nonconforming rows in the target table, issue the
SET statement again to switch the disabled index to the enabled
mode. This time the index is enabled, and no integrity violation error
message is returned because all rows in the target table now satisfy
the new unique-index requirement.
Object Modes for Duplicate Indexes
Object Modes for
Duplicate Indexes
DISABLED
ENABLED
SQL Statements 1-131
CREATE INDEX
If you create a duplicate index, you can set the object mode of the index to the
disabled or enabled mode. The following table explains these modes.
Object Mode
Effect
disabled
A duplicate index is created in disabled mode. The disabled index
is not updated after insert, delete, and update operations that
modify the base table. Because the contents of the disabled index
are not up to date, the optimizer does not use the index during the
execution of queries.
enabled
A duplicate index is created in enabled mode. The enabled index is
updated after insert, delete, and update operations that modify the
base table. Because the contents of the enabled index are up to date,
the optimizer uses the index during the execution of queries. If an
insert or update operation causes a duplicate key value to be added
to a duplicate enabled index, the statement does not fail.
Specifying Object Modes for Duplicate Indexes
You must observe the following rules when you specify object modes for
duplicate indexes in CREATE INDEX statements:
■
You can set a duplicate index to the enabled or disabled mode, but
you cannot set a duplicate index to the filtering mode.
■
If you do not specify the object mode of a duplicate index explicitly,
the default mode is enabled.
How the Database Server Treats Disabled Indexes
Whether a disabled index is a unique or duplicate index, the database server
effectively ignores the index during data-manipulation operations.
When an index is disabled, the database server stops updating it and stops
using it during queries, but the catalog information about the disabled index
is retained. So you cannot create a new index on a column or set of columns
if a disabled index on that column or set of columns already exists.
Similarly, you cannot create an active (not disabled) unique, foreign-key, or
primary-key constraint on a column or set of columns if the indexes needed
by the active constraint exist and are disabled.
1-132
Informix Guide to SQL: Syntax
CREATE INDEX
References
See the ALTER INDEX, DROP INDEX, and CREATE TABLE statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussions of indexes in
Chapter 3. In addition, see the INFORMIX-OnLine Dynamic Server Performance Guide for information about performance issues with indexes.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
CREATE INDEX statement.
SQL Statements 1-133
CREATE PROCEDURE
CREATE PROCEDURE
Use the CREATE PROCEDURE statement to name and define a stored
procedure.
Syntax
+
CREATE
PROCEDURE
DBA
Procedure
Name
p. 1-754
(
)
,
Parameter
p. 1-136
Statement
Block
p. 1-140
END
PROCEDURE
;
,
DOCUMENT
Element
pathname
RETURNING
Clause
p. 1-138
Purpose
The pathname and filename of
the listing file that is to contain
warnings generated during the
compilation of the procedure.
See “WITH LISTING IN Option”
on page 1-139 for the default
action taken when you omit the
pathname.
Quoted String
p. 1-757
WITH
LISTING IN
Restrictions
The specified pathname must
exist on the computer where the
database resides.
' pathname '
Syntax
The pathname and
filename must
conform to the
conventions of your
operating system.
Usage
You must have the Resource privilege on a database to create a procedure.
The entire length of a CREATE PROCEDURE statement must be less than 64
kilobytes. This length is the literal length of the CREATE PROCEDURE
statement, including blank space and tabs.
1-134
Informix Guide to SQL: Syntax
CREATE PROCEDURE
If the statement block portion of the CREATE PROCEDURE statement is empty,
no operation takes place when you call the procedure. You might use such a
procedure in the development stage when you want to establish the existence
of a procedure but have not yet coded it.
Warning: When you specify a date value in an expression in any statement in the
statement block, make sure to specify 4 digits instead of 2 digits for the year. When
you specify a 4-digit year, the DBCENTURY environment variable has no effect on
how the database server interprets the date value. When you specify a 2-digit year,
the DBCENTURY environment variable can affect how the database server interprets
the date value, so the stored procedure might produce unpredictable results. See the
“Informix Guide to SQL: Reference” for more information on the DBCENTURY
environment variable.
ESQL
SE
You can use a CREATE PROCEDURE statement only within a PREPARE
statement. If you want to create a procedure for which the text is known at
compile time, you must use a CREATE PROCEDURE FROM statement. ♦
You cannot use a ROLLBACK WORK statement to undo a CREATE
PROCEDURE statement. If you roll back a transaction that contains a CREATE
PROCEDURE statement, the procedure remains, and you do not receive an
error message. ♦
DBA Option
If you create a procedure using the DBA option, it is known as a DBAprivileged procedure. If you do not use the DBA option, the procedure is
known as an owner-privileged procedure. The privileges associated with the
execution of a procedure are determined by whether the procedure is created
with the DBA keyword. See Chapter 12 of the Informix Guide to SQL: Tutorial
for more information.
If you create an owner-privileged procedure in a database that is not
ANSI-compliant, the NODEFDAC environment variable prevents privileges
on that procedure from being granted to PUBLIC. See the Informix Guide to
SQL: Reference for further information on the NODEFDAC environment
variable.
SQL Statements 1-135
CREATE PROCEDURE
Parameter Syntax and Use
Parameter
SQL Data Type
(Subset)
p. 1-137
variable
name
LIKE
table
name
.
REFERENCES
DEFAULT
column
name
BYTE
TEXT
Element
column name
default value
table name
variable name
Purpose
The name of a column whose
data type is assigned as variable
name
The default value that a
procedure uses if you do not
supply a value for variable name
when you call the procedure
The name of the table that
contains column name
The name of a parameter for
which you supply a value when
you call the procedure
default
value
DEFAULT
NULL
Restrictions
The column must exist in the
specified table.
Syntax
Identifier, p. 1-723
The default value must conform Expression, p. 1-671
to the data type of variable name.
The table must exist in the
database.
You can specify zero, one, or
more parameters in a CREATE
PROCEDURE statement.
Identifier, p. 1-723
Identifier, p. 1-723
To define a parameter within the CREATE PROCEDURE statement, you must
specify its name. You must also specify its data type. You can specify the data
type directly or use the LIKE or REFERENCES clauses to identify the data type.
Specifying a Default Value for a Parameter
You can use the DEFAULT keyword followed by an expression to specify a
default value for a parameter. If you provide a default value for a parameter,
and the procedure is called with fewer arguments than were defined for that
procedure, the default value is used. If you do not provide a default value for
a parameter, and the procedure is called with fewer arguments than were
defined for that procedure, the calling application receives an error.
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Informix Guide to SQL: Syntax
CREATE PROCEDURE
The following example shows a CREATE PROCEDURE statement that specifies
a default value for a parameter. This procedure finds the square of the i
parameter. If the procedure is called without specifying the argument for the
i parameter, the database server uses the default value 0 for the i parameter.
CREATE PROCEDURE square_w_default
(i INT DEFAULT 0) {Specifies default value of i}
RETURNING INT; {Specifies return of INT value}
DEFINE j INT; {Defines procedure variable j}
LET j = i * i; {Finds square of i and assigns it to j}
RETURN j; {Returns value of j to calling module}
END PROCEDURE;
Warning: When you specify a date value as the default value for a parameter, make
sure to specify 4 digits instead of 2 digits for the year. When you specify a 4-digit year,
the DBCENTURY environment variable has no effect on how the database server
interprets the date value. When you specify a 2-digit year, the DBCENTURY environment variable can affect how the database server interprets the date value, so the
stored procedure might not use the default value that you intended. See the “Informix
Guide to SQL: Reference” for more information on the DBCENTURY environment
variable.
Subset of SQL Data Types Allowed in the Parameter List
The SQL Data Type subset includes all the SQL data types except SERIAL,
TEXT, and BYTE. For the complete syntax of all the SQL data types, see
page 1-664.
To use a TEXT or BYTE data type, use the REFERENCES keyword, as the
diagram on page 1-136 shows.
Referencing TEXT or BYTE Values
Use the REFERENCES clause to specify that a parameter contains TEXT or
BYTE data. If you use the DEFAULT NULL option in the REFERENCES clause,
and you call the procedure without a parameter, a null value is used.
SQL Statements 1-137
CREATE PROCEDURE
RETURNING Clause
RETURNING
Clause
,
;
SQL Data Type
(Subset)
p. 1-137
RETURNING
REFERENCES
BYTE
TEXT
In the following examples, the RETURNING clause can be a noncursory
procedure or a cursory procedure. In the first example, the RETURNING
clause can return zero or one value if it is a noncursory procedure. However,
if this clause is associated with a cursory procedure, it returns more than one
row from a table, and each returned row contains zero or one value. In the
second example, the RETURNING clause can return zero or two values if it is
a noncursory procedure. However, if this clause is associated with a cursory
procedure, it returns more than one row from a table and each returned row
contains zero or two values.
RETURNING INT;
RETURNING INT, INT;
The receiving procedure or program must be written appropriately to accept
the information.
Adding Comments to the Procedure
To add a comment to any line of a procedure, place a double-dash (--) before
the comment or enclose the comment in curly brackets ({}). The double dash
complies with the ANSI standard. The curly brackets are an Informix
extension to the ANSI standard.
For examples of comments in procedures, see “Specifying a Default Value for
a Parameter” on page 1-136. For detailed information on the double-dash (--)
and curly-brackets ({}) symbols, see “How to Enter SQL Comments” on
page 1-9.
1-138
Informix Guide to SQL: Syntax
CREATE PROCEDURE
Describing the Procedure in the DOCUMENT Clause
The quoted string or strings in the DOCUMENT clause provide a synopsis and
description of the procedure. The DOCUMENT text is intended for the user of
the procedure. Anyone with access to the database can query the
sysprocbody system catalog table to obtain a description of one or all the
procedures stored in the database.
For example, to find the description of the procedure called do_something,
execute the following query:
SELECT data FROM sysprocbody b, sysprocedures p
= p.procid {join between the two catalogs}
WHERE b.procid
AND
p.procname = 'do_something' {look for procedure do_something}
{ want user document }
AND b.datakey = 'D'
ORDER BY b.seqno;
{
... in order
}
The rows returned are the complete text as supplied in the DOCUMENT
clause of the CREATE PROCEDURE statement.
CREATE PROCEDURE ret_sal (dep_no INT, name CHAR(8) default user)
RETURNING INT;
.
.
.
END PROCEDURE
DOCUMENT
'Usage: salary (dept [required], name [default: your name])',
'returns your (or someone else’s) salary',
'Warning: This procedure sends mail on illegal use'
WITH LISTING IN '/usr/tmp/sal.warnings';
WITH LISTING IN Option
The WITH LISTING IN option specifies a filename where compile time
warnings are sent. This listing file is created on the computer where the
database resides. After you compile a procedure, this file holds one or more
warning messages.
If you specify a filename but not a directory in the pathname variable, the
default directory is your home directory on the computer where the database
resides. If you do not have a home directory on this computer, the file is
created in the root directory (the directory named “/”).
If you do not use the WITH LISTING IN option, the compiler does not generate
a list of warnings.
SQL Statements 1-139
CREATE PROCEDURE
The Statement Block
Statement Block
DEFINE
Statement
p. 2-8
CALL Statement
p. 2-4
ON
EXCEPTION
Statement
p. 2-34
CONTINUE
Statement
p. 2-7
EXECUTE PROCEDURE
Statement
p. 1-293
EXIT Statement
p. 2-16
FOR Statement
p. 2-18
FOREACH Statement
p. 2-23
IF Statement
p. 2-27
LET Statement
p. 2-31
RAISE EXCEPTION
Statement
p. 2-39
RETURN Statement
p. 2-41
SYSTEM Statement
p. 2-43
TRACE Statement
p. 2-46
WHILE Statement
p. 2-49
Subset of SQL
Statement
p. 1-141
BEGIN
1-140
Informix Guide to SQL: Syntax
Statement
Block
;
END
CREATE PROCEDURE
The statement block can be empty, which results in a procedure that does
nothing. Also, you cannot close the current database or select a new database
within a procedure. And you cannot drop the current procedure within a
procedure. You can, however, drop another procedure.
Subset of SQL Statements Allowed in the Statement Block
You can use any SQL statement in the statement block, except those listed in
Figure 1-1.
Figure 1-1
SQL Statements That Cannot Be Used in a Stored Procedure
CHECK TABLE
FREE
CLOSE
GET DESCRIPTOR
CLOSE DATABASE
INFO
CONNECT
CREATE DATABASE
LOAD
OPEN
CREATE PROCEDURE
OUTPUT
CREATE PROCEDURE FROM
PREPARE
DATABASE
DECLARE
DESCRIBE
PUT
REPAIR
EXECUTE
SET DESCRIPTOR
EXECUTE IMMEDIATE
START DATABASE
FETCH
FLUSH
UNLOAD
WHENEVER
ROLLFORWARD DATABASE
Restrictions on SELECT Statement
You can use a SELECT statement in only two cases:
■
You can use the INTO TEMP clause to put the results of the SELECT
statement into a temporary table.
■
You can use the SELECT...INTO form of the SELECT statement to put
the resulting values into procedure variables.
SQL Statements 1-141
CREATE PROCEDURE
Support for Roles and User Identity
You can use roles with stored procedures. You can execute role-related
statements (CREATE ROLE, DROP ROLE, and SET ROLE) and SET SESSION
AUTHORIZATION statements within a stored procedure. You can also grant
privileges to roles with the GRANT statement within a procedure. Privileges
that a user has acquired through enabling a role or by a SET SESSION
AUTHORIZATION statement are not relinquished when a procedure is
executed.
For further information about roles, see the CREATE ROLE, DROP ROLE,
GRANT, REVOKE, and SET ROLE statements in this guide.
Restrictions on a Procedure Called in a Data Manipulation Statement
If a stored procedure is called as part of an INSERT, UPDATE, DELETE, or
SELECT statement, the called procedure cannot execute any statement listed
in Figure 1-2. This restriction ensures that the stored procedure cannot make
changes that affect the SQL statement that contains the procedure call.
Figure 1-2
SQL Statements Not Allowed in a Procedure That a Data Manipulation Statement Calls
ALTER FRAGMENT
ALTER INDEX
ALTER OPTICAL
ALTER TABLE
BEGIN WORK
COMMIT WORK
CREATE TRIGGER
DELETE
DROP DATABASE
DROP INDEX
DROP OPTICAL
1-142
Informix Guide to SQL: Syntax
DROP SYNONYM
DROP TABLE
DROP TRIGGER
DROP VIEW
INSERT
RENAME COLUMN
RENAME TABLE
ROLLBACK WORK
SET CONSTRAINTS
UPDATE
CREATE PROCEDURE
For example, if you use the following INSERT statement, the execution of the
called procedure dup_name is restricted:
CREATE PROCEDURE sp_insert ()
.
.
.
INSERT INTO q_customer
VALUES (SELECT * FROM customer
WHERE dup_name ('lname') = 2)
.
.
.
END PROCEDURE;
In this example, dup_name cannot execute the statements listed in
Figure 1-2. However, if dup_name is called within a statement that is not an
INSERT, UPDATE, SELECT, or DELETE statement (namely EXECUTE
PROCEDURE), dup_name can execute the statements listed in Figure 1-2.
You can use the BEGIN WORK and COMMIT WORK statements in procedures.
You can start a transaction, finish a transaction, or start and finish a transaction in a procedure. If you start a transaction in a procedure that is executed
remotely, you must finish the transaction before the procedure exits.
References
See the CREATE PROCEDURE FROM, DROP PROCEDURE, GRANT, EXECUTE
PROCEDURE, PREPARE, UPDATE STATISTICS, and REVOKE statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of creating and using
stored procedures in Chapter 12.
SQL Statements 1-143
CREATE PROCEDURE FROM
CREATE PROCEDURE FROM
Use the CREATE PROCEDURE FROM statement to create a procedure. The
actual text of the procedure resides in a separate file.
Syntax
ESQL
+
CREATE PROCEDURE FROM
' filename'
variable
name
Element
filename
variable name
Purpose
The pathname and filename of
the file that contains the full text
of a CREATE PROCEDURE
statement. The default
pathname is the current
directory.
The name of a program variable
that holds the value of filename
Restrictions
The specified file must exist.
Syntax
The pathname and
filename must
conform to the
conventions of your
operating system.
The file that is specified in the
program variable must exist.
The name must
conform to
language-specific
rules for variable
names.
Usage
The filename that is provided in this statement is relative; if a simple filename
is provided, the database server looks for the file in the current directory.
References
See the CREATE PROCEDURE statement in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of creating and using
stored procedures in Chapter 12.
1-144
Informix Guide to SQL: Syntax
CREATE ROLE
CREATE ROLE
Use the CREATE ROLE statement to create a new role.
Syntax
+
OL
Element
role name
CREATE ROLE
role name
Purpose
Restrictions
Syntax
Name assigned to a role created Maximum number of characters Identifier, p. 1-723
by the DBA
is 8.
A role name cannot be a user
name known to the database
server or the operating system of
the database server. A role name
cannot be in the username
column of the sysusers system
catalog table or in the grantor or
grantee columns of the
systabauth, syscolauth,
sysprocauth, sysfragauth, and
sysroleauth system catalog
tables.
Usage
The database administrator (DBA) uses the CREATE ROLE statement to create
a new role. A role can be considered as a classification, with privileges on
database objects granted to the role. The DBA can assign the privileges of a
related work task, such as engineer, to a role and then grant that role to users,
instead of granting the same set of privileges to every user.
After a role is created, the DBA can use the GRANT statement to grant the role
to users or to other roles. When a role is granted to a user, the user must use
the SET ROLE statement to enable the role. Only then can the user use the
privileges of the role.
SQL Statements 1-145
CREATE SCHEMA
CREATE SCHEMA
Purpose
The CREATE SCHEMA statement allows you to issue a block of CREATE and
GRANT statements as a unit. It allows you to specify an owner of your choice
for all objects that the CREATE SCHEMA statement creates.
Syntax
DB
CREATE SCHEMA
AUTHORIZATION
CREATE TABLE
Statement
p. 1-154
user
name
+
CREATE INDEX
Statement
p. 1-109
CREATE VIEW
Statement
p. 1-224
+
CREATE SYNONYM
Statement
p. 1-150
GRANT
Statement
p. 1-340
CREATE TRIGGER
Statement
p. 1-192
OP
CREATE OPTICAL
CLUSTER
Statement
see INFORMIXOnLine/Optical
User Manual
SQL Statements 1-147
CREATE SCHEMA
Element
user name
Purpose
The name of the user who will
own the objects that the CREATE
SCHEMA statement creates
Restrictions
Syntax
If the user who issues the
Identifier, p. 1-723
CREATE SCHEMA statement has
the Resource privilege, user name
must be the name of this user. If
the user who issues the CREATE
SCHEMA statement has the DBA
privilege, user name can be the
name of this user or another
user.
Usage
You cannot issue the CREATE SCHEMA statement until you create the affected
database.
Users with the Resource privilege can create a schema for themselves. In this
case, user name must be the name of the person with the Resource privilege
who is running the CREATE SCHEMA statement. Anyone with the DBA
privilege can also create a schema for someone else. In this case, user name can
identify a user other than the person who is running the CREATE SCHEMA
statement.
You can put CREATE and GRANT statements in any logical order within the
statement, as the following example shows. Statements are considered part
of the CREATE SCHEMA statement until a semicolon or an end-of-file symbol
is reached.
CREATE SCHEMA AUTHORIZATION sarah
CREATE TABLE mytable (mytime DATE, mytext TEXT)
GRANT SELECT, UPDATE, DELETE ON mytable TO rick
CREATE VIEW myview AS
SELECT * FROM mytable WHERE mytime > '12/31/1993'
CREATE INDEX idxtime ON mytable (mytime);
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Informix Guide to SQL: Syntax
CREATE SCHEMA
Creating Objects Within CREATE SCHEMA
All objects that a CREATE SCHEMA statement creates are owned by user name,
even if you do not explicitly name each object. If you are the DBA, you can
create objects for another user. If you are not the DBA, and you try to create
an object for an owner other than yourself, you receive an error message.
Granting Privileges Within CREATE SCHEMA
You can only grant privileges with the CREATE SCHEMA statement; you
cannot revoke or drop privileges.
Creating Objects or Granting Privileges Outside CREATE
SCHEMA
If you create an object or use the GRANT statement outside a CREATE
SCHEMA statement, you receive warnings if you use the -ansi flag or set
DBANSIWARN.
References
See the CREATE INDEX, CREATE SYNONYM, CREATE TABLE, CREATE VIEW,
and GRANT statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of creating the
database in Chapter 9.
SQL Statements 1-149
CREATE SYNONYM
CREATE SYNONYM
Use the CREATE SYNONYM statement to provide an alternative name for a
table or view.
Syntax
+
CREATE
SYNONYM
PUBLIC
Synonym
Name
p. 1-766
FOR
PRIVATE
Table Name
p. 1-768
View Name
p. 1-772
Usage
Users have the same privileges for a synonym that they have for the table to
which the synonym applies.
The synonym name must be unique; that is, the synonym name cannot be the
same as another database object, such as a table, view, or temporary table.
Once a synonym is created, it persists until the owner executes the DROP
SYNONYM statement. This property distinguishes a synonym from an alias
that you can use in the FROM clause of a SELECT statement. The alias persists
for the existence of the SELECT statement. If a synonym refers to a table or
view in the same database, the synonym is automatically dropped if you
drop the referenced table or view.
You cannot create a synonym for a synonym in the same database.
ANSI
The owner of the synonym (owner.synonym) qualifies the name of a synonym.
The identifier owner.synonym must be unique among all the synonyms, tables,
temporary tables, and views in the database. You must specify owner when
you refer to a synonym that another user owns. The following example
shows this convention:
CREATE SYNONYM emp FOR accting.employee
♦
1-150
Informix Guide to SQL: Syntax
CREATE SYNONYM
SE
You cannot use a ROLLBACK WORK statement to undo a CREATE SYNONYM
statement. If you roll back a transaction that contains a CREATE SYNONYM
statement, the synonym remains, and you do not receive an error message. ♦
You can create a synonym for any table or view in any database on your
database server. Use the owner. convention if the table is part of an
ANSI-compliant database. The following example shows a synonym for a
table outside the current database. It assumes that you are working on the
same database server that contains the payables database.
CREATE SYNONYM mysum FOR payables:jean.summary
You can create a synonym for any table or view that exists on any networked
database server as well as on the database server that contains your current
database. The database server that holds the table must be on-line when you
create the synonym. In a network, INFORMIX-OnLine Dynamic Server verifies
that the object of the synonym exists when you create the
synonym.
The following example shows how to create a synonym for an object that is
not in the current database:
CREATE SYNONYM mysum FOR payables@phoenix:jean.summary
The identifier mysum now refers to the table jean.summary, which is in the
payables database on the phoenix database server. Note that if the summary
table is dropped from the payables database, the mysum synonym is left
intact. Subsequent attempts to use mysum return the error Table not found.
PUBLIC and PRIVATE Synonyms
If you use the PUBLIC keyword (or no keyword at all), anyone who has access
to the database can use your synonym. If a synonym is public, a user does not
need to know the name of the owner of the synonym. Any synonym in a
database that is not ANSI compliant and was created before Version 5.0 of the
database server is a public synonym.
ANSI
Synonyms are always private. If you use the PUBLIC or PRIVATE keywords,
you receive a syntax error. ♦
SQL Statements 1-151
CREATE SYNONYM
If you use the PRIVATE keyword, the synonym can be used only by the owner
of the synonym or if the owner’s name is specified explicitly with the
synonym. More than one private synonym with the same name can exist in
the same database. However, a different user must own each synonym with
that name.
You can own only one synonym with a given name; you cannot create both
private and public synonyms with the same name. For example, the
following code generates an error:
CREATE SYNONYM our_custs FOR customer;
CREATE PRIVATE SYNONYM our_custs FOR cust_calls;-- ERROR!!!
Synonyms with the Same Name
If you own a private synonym, and a public synonym exists with the same
name, when you use the synonym by its unqualified name, the private
synonym is used.
If you use DROP SYNONYM with a synonym, and multiple synonyms exist
with the same name, the private synonym is dropped. If you issue the DROP
SYNONYM statement again, the public synonym is dropped.
Chaining Synonyms with INFORMIX-OnLine Dynamic Server
If you create a synonym for a table that is not in the current database, and this
table is dropped, the synonym stays in place. You can create a new synonym
for the dropped table, with the name of the dropped table as the synonym
name, which points to another external or remote table. In this way, you can
move a table to a new location and chain synonyms together so that the
original synonyms remain valid. (You can chain as many as 16 synonyms in
this manner.)
The following steps chain two synonyms together for the customer table,
which will ultimately reside on the zoo database server (the CREATE TABLE
statements are not complete):
1.
In the stores7 database on the database server that is called training,
issue the following statement:
CREATE TABLE customer (lname CHAR(15)...)
2.
On the database server called accntg, issue the following statement:
CREATE SYNONYM cust FOR stores7@training:customer
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Informix Guide to SQL: Syntax
CREATE SYNONYM
3.
On the database server called zoo, issue the following statement:
CREATE TABLE customer (lname CHAR(15)...)
4.
On the database server called training, issue the following
statement:
DROP TABLE customer
CREATE SYNONYM customer FOR stores7@zoo:customer
The synonym cust on the accntg database server now points to the customer
table on the zoo database server.
The following steps show an example of chaining two synonyms together
and changing the table to which a synonym points:
1.
On the database server called training, issue the following
statement:
CREATE TABLE customer (lname CHAR(15)...)
2.
On the database server called accntg, issue the following statement:
CREATE SYNONYM cust FOR stores7@training:customer
3.
On the database server called training, issue the following
statement:
DROP TABLE customer
CREATE TABLE customer (lastname CHAR(20)...)
The synonym cust on the accntg database server now points to a new version
of the customer table on the training database server.
References
See the DROP SYNONYM statement in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of synonyms in
Chapter 5 and Chapter 11
SQL Statements 1-153
CREATE TABLE
CREATE TABLE
Use the CREATE TABLE statement to create a new table in the current
database, place data-integrity constraints on its columns or on a combination
of its columns, designate the size of its initial and subsequent extents, and
specify how to lock each table. The statement is also used to fragment tables
into separate dbspaces.
Syntax
,
CREATE
TABLE
Table
Name
p. 1-768
(
Column
Definition
p. 1-158
,
,
+
Temp
Table
Clause
p. 1-177
Table-Level
Constraint
Definition
p. 1-174
)
OL
WITH
ROWIDS
p. 1-182
Storage
Option
p. 1-183
Usage
Table names must be unique within a database. However, although
temporary table names must be different from existing table, view, or
synonym names in the current database, they need not be different from
other temporary table names used by other users.
ANSI
SE
DB
1-154
In an ANSI-compliant database, the combination owner.tablename must be
unique within the database. ♦
You cannot use a ROLLBACK WORK statement to undo a CREATE TABLE
statement. If you roll back a transaction that contains a CREATE TABLE
statement, the table remains, and you do not receive an error message. ♦
Using the CREATE TABLE statement outside the CREATE SCHEMA statement
generates warnings if you use the -ansi flag or set DBANSIWARN. ♦
Informix Guide to SQL: Syntax
CREATE TABLE
ESQL
Using the CREATE TABLE statement generates warnings if you use the -ansi
flag or set DBANSIWARN. ♦
Privileges on Tables
By default, all users who have been granted the Connect privilege to a
database have all access privileges (except Alter and References) to the new
table. To further restrict access, use the REVOKE statement to take all access
away from PUBLIC (everyone on the system). Then, use the GRANT statement
to designate the access privileges that you want to give to specific users.
When set to yes, the environment variable NODEFDAC prevents default
privileges on a new table in a database that is not ANSI compliant from being
granted to PUBLIC. For information about preventing privileges from being
granted to PUBLIC, see the NODEFDAC environment variable in the Informix
Guide to SQL: Reference.
ANSI
In an ANSI-compliant database, no default table-level privileges exist. You
must grant these privileges explicitly. ♦
Defining Constraints
When you create a table, several elements must be defined. For example, the
table and columns within that table must have unique names. Also, every
table column must have at least a data type associated with it. You can also,
optionally, place several constraints on a given column. For example, you can
indicate that the column has a specific default value or that data entered into
the column must be checked to meet a specific data requirement.
Putting a constraint on a column is similar to putting an index on a column
(using the CREATE INDEX statement). However, if you use constraints instead
of indexes, you can also implement data-integrity constraints and turn
effective checking off and on. For information on data-integrity constraints,
refer to Chapter 3 of the Informix Guide to SQL: Tutorial. For information on
effective checking, see the SET statement on page 1-501.
Important: In a database without logging, detached checking is the only constraintchecking mode available. Detached checking means that constraint checking is
performed on a row-by-row basis.
SQL Statements 1-155
CREATE TABLE
You can define constraints at either the column or table level. If you choose to
define constraints at the column level, you cannot have multiple-column
constraints. In other words, the constraint created at the column level can
apply only to a single column. If you choose to define constraints at the table
level, you can apply constraints to single or multiple columns. At either level,
single-column constraints are treated the same way.
Whenever you place a data restriction on a column, a constraint is created
automatically. You have the option of specifying a name for the constraint. If
you choose not to specify a name for the constraint, the database server
creates a default constraint name for you automatically.
When you create a constraint of any type, the name of the constraint must be
unique within the database.
ANSI
When you create a constraint of any type, the owner.name combination (the
combination of the owner name and constraint name) must be unique within
the database. ♦
Limits on Constraint Definitions
You can include 16 columns in a list of columns for a unique, primary-key, or
referential constraint. The total length of all columns cannot exceed 255 bytes.
SE
You can use up to eight columns, inclusive, in an INFORMIX-SE list of
columns. The total length of all columns cannot exceed 120 bytes. ♦
You cannot place a constraint on a violations or diagnostics table. For further
information on violations and diagnostics tables, see the START VIOLATIONS
TABLE statement on page 1-584.
Adding or Dropping Constraints
After you have used the CREATE TABLE statement to place constraints on a
column or set of columns, you must use the ALTER TABLE statement to add
or drop the constraint from the column or composite column list.
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CREATE TABLE
Enforcing Primary-Key, Unique, and Referential Constraints
Primary-key, unique, and referential constraints are implemented as an
ascending index that allows only unique entries or an ascending index that
allows duplicates. When one of these constraints is placed on a column, the
database server performs the following functions:
■
Creates a unique index for a unique or primary-key constraint
■
Creates a non-unique index for the columns specified in the
referential constraint
However, if a constraint already was created on the same column or set of
columns, another index is not built for the constraints. Instead, the existing
index is shared by the constraints. If the existing index is non-unique, it is
upgraded if a unique or primary-key constraint is placed on that column.
Because these constraints are enforced through indexes, you cannot create an
index (using the CREATE INDEX statement) for a column that is of the same
data type as the constraint placed on that column. For example, if a unique
constraint exists on a column, you can create neither an ascending unique
index for that column nor a duplicate ascending index.
Constraint Names
A row is added to the sysindexes system catalog table for each new primarykey, unique, or referential constraint that does not share an index with an
existing constraint. The index name in the sysindexes system catalog table is
created with the following format:
[space]<tabid>_<constraint id>
In this format, tabid and constraint id are from the systables and
sysconstraints system catalog tables, respectively. For example, the index
name might be something like this: " 121_13" (quotes used to show the space).
The constraint name must be unique within the database. If you do not
specify a constraint name, the database server generates one for the
sysconstraints system catalog table using the following template:
<constraint type><tabid>_<constraint id>
SQL Statements 1-157
CREATE TABLE
In this template, constraint type is the letter u for unique or primary-key
constraints, r for referential constraints, c for check constraints, and n for not
null constraints. For example, the constraint name for a unique constraint
might look like this: u111_14. If the name conflicts with an existing identifier,
the database server returns an error, and you must then supply a constraint
name.
Object Modes for Constraints
You can specify the object mode for any type of column-level or table-level
constraint. You can set the object mode of the constraint to the enabled,
disabled, or filtering mode. See “Constraint-Mode Definitions” on page 1-163
for further information on object modes.
Column-Definition Option
Column
Definition
column
name
Data Type
p. 1-664
DEFAULT
Clause
p. 1-159
Element
column name
Purpose
The name of a column in the
table
Column-Level
Constraint
Definition
p. 1-162
Restrictions
Name must be unique within a
table, but you can use the same
names in different tables in the
same database.
Syntax
Identifier, p. 1-723
Use the column-definition portion of the CREATE TABLE statement to list the
name, data type, default values, and constraints of a single column as well as
to indicate whether the column does not allow duplicate values.
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CREATE TABLE
The DEFAULT Clause
DEFAULT
Clause
literal
DEFAULT
NULL
+
CURRENT
p. 1-680
+
DATETIME
Field Qualifier
p. 1-669
USER
p. 1-678
TODAY
p. 1-680
OL
+
+
SITENAME
p. 1-679
DBSERVERNAME
p. 1-679
Element
literal
Purpose
A literal term that defines alpha
or numeric constant characters
to be used as the default value
for the column
Restrictions
Term must be appropriate type
for the column. See “Literal
Terms as Default Values” on
page 1-160.
Syntax
Expression, p. 1-671
The default value is inserted into the column when an explicit value is not
specified. If a default is not specified, and the column allows nulls, the default
is NULL. If you designate NULL as the default value for a column, you cannot
specify a not null constraint as part of the column definition.
You cannot designate default values for serial columns. If the column is TEXT
or BYTE data type, you can only designate NULL as the default value.
SQL Statements 1-159
CREATE TABLE
Literal Terms as Default Values
You can designate literal terms as default values. A literal term is a string of
character or numeric constant characters that you define. To use a literal term
as a default value, you must adhere to the following rules.
Use a Literal
With Columns of Data Type
INTEGER
INTEGER, SMALLINT, DECIMAL, MONEY, FLOAT,
SMALLFLOAT
DECIMAL
DECIMAL, MONEY, FLOAT, SMALLFLOAT
CHARACTER
CHAR, NCHAR, NVARCHAR, VARCHAR, DATE
INTERVAL
INTERVAL
DATETIME
DATETIME
Characters must be enclosed in quotation marks. Date literals must be of the
format specified with the DBDATE environment variable. If DBDATE is not
set, the format mm/dd/yyyy is assumed.
For information on using a literal INTERVAL, refer to the Literal INTERVAL
segment on page 1-749. For more information on using a literal DATETIME,
refer to the Literal DATETIME segment on page 1-746.
You cannot designate NULL as a default value for a column that is part of a
primary key.
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Informix Guide to SQL: Syntax
CREATE TABLE
Data Type Requirements for Certain Columns
The following table indicates the data type requirements for columns that
specify the CURRENT, DBSERVERNAME, SITENAME, TODAY, or USER
functions as the default value.
Function Name
Data Type Requirement
CURRENT
DATETIME column with matching qualifier
DBSERVERNAME
CHAR, NCHAR, NVARCHAR, or VARCHAR column at least
18 characters long
SITENAME
CHAR, NCHAR, NVARCHAR, or VARCHAR column at least
18 characters long
TODAY
DATE column
USER
CHAR or VARCHAR column at least 8 characters long
Example of Default Values in Column Definitions
The following example creates a table called accounts. In accounts, the
acc_num, acc_type, and acc_descr columns have literal default values. The
acc_id column defaults to the user’s login name.
CREATE TABLE accounts (
acc_num INTEGER DEFAULT 0001,
acc_type CHAR(1) DEFAULT 'A',
acc_descr CHAR(20) DEFAULT 'New Account',
acc_id CHAR(8) DEFAULT USER)
SQL Statements 1-161
CREATE TABLE
Specifying a Not Null Constraint in a Column Definition
If you do not indicate a default value for a column, the default is NULL unless
you place a not null constraint on the column. In this case, no default value
exists for the column. The following example creates the newitems table. In
newitems, the column manucode does not have a default value nor does it
allow nulls.
CREATE TABLE newitems (
newitem_num INTEGER,
manucode CHAR(3) NOT NULL,
promotype INTEGER,
descrip CHAR(20))
If you place a not null constraint on a column (and no default value is
specified), you must enter a value into this column when you insert a row or
update that column in a row. If you do not enter a value, the database server
returns an error.
Column-Level Constraint-Definition Option
Column-Level
Constraint
Definition
UNIQUE
+
NOT
NULL
+
DISTINCT
+
ConstraintMode
Definitions
p. 1-163
PRIMARY
KEY
REFERENCES
Clause
p. 1-165
CHECK
Clause
p. 1-172
1-162
Informix Guide to SQL: Syntax
ConstraintMode
Definitions
p. 1-163
CREATE TABLE
Unlike the table-level constraint-definition option, constraints at the column
level are limited to a single column. In other words, you cannot create not
null, check, unique, primary, or foreign-key multiple-column constraints. For
more information on the unique, primary-key, and check constraints, see
“Table-Level Constraint-Definition Option” on page 1-174.
The following example creates a simple table with two constraints, a
primary-key constraint named num on the acc_num column and a unique
constraint named code on the acc_code column:
CREATE TABLE accounts (
acc_num INTEGER PRIMARY KEY CONSTRAINT num,
acc_code INTEGER UNIQUE CONSTRAINT code,
acc_descr CHAR(30))
Using Blob Data Types in Constraints
You cannot place a unique, primary-key, or referential constraint on BYTE or
TEXT columns. However, you can check for null or non-null values if you
place a check constraint on a BYTE or TEXT column.
Constraint-Mode Definitions
Constraint-Mode
Definitions
DISABLED
CONSTRAINT
Constraint
Name
p. 1-658
ENABLED
FILTERING
WITHOUT
ERROR
WITH
ERROR
SQL Statements 1-163
CREATE TABLE
You can use the Constraint-Mode Definitions option for the following
purposes:
■
You can assign a name to a column-level or table-level constraint.
■
You can set any type of column-level constraint or table-level
constraint to the disabled, enabled, or filtering-object modes.
Description of Constraint Modes
You can set constraints in the following modes: disabled, enabled, and
filtering. The following list explains these modes and options.
Constraint
Mode
Effect
disabled
A constraint created in disabled mode is not enforced during insert,
delete, and update operations.
enabled
A constraint created in enabled mode is enforced during insert,
delete, and update operations. If a target row causes a violation of
the constraint, the statement fails.
filtering
A constraint created in filtering mode is enforced during insert,
delete, and update operations. If a target row causes a violation of
the constraint, the statement continues processing, but the bad row
is written to the violations table associated with the target table.
Diagnostic information about the constraint violation is written to
the diagnostics table associated with the target table.
If you choose filtering mode, you can specify the WITHOUT ERROR or WITH
ERROR options. The following list explains these options.
1-164
Error Option
Effect
WITHOUT
ERROR
When a filtering-mode constraint is violated during an insert,
delete, or update operation, no integrity-violation error is returned
to the user.
WITH ERROR
When a filtering-mode constraint is violated during an insert,
delete, or update operation, an integrity-violation error is returned
to the user.
Informix Guide to SQL: Syntax
CREATE TABLE
Using Constraint-Mode Definitions
You must observe the following rules concerning the use of constraint-mode
definitions:
■
If you do not specify the object mode of a column-level constraint or
table-level constraint explicitly, the default mode is enabled.
■
If you do not specify the WITH ERROR or WITHOUT ERROR option for
a filtering-mode constraint, the default error option is WITHOUT
ERROR.
■
Constraints defined on temporary tables are always in the enabled
mode. You cannot create a constraint on a temporary table in the
disabled or filtering mode, nor can you use the SET statement to
switch the object mode of a constraint on a temporary table to the
disabled or filtering mode.
■
You cannot assign a name to a not null constraint on a temporary
table.
■
You cannot create a constraint on a table that is serving as a violations
or diagnostics table for another table.
The REFERENCES Clause
REFERENCES
Clause
REFERENCES
table
name
OL
+
,
(
column
name
)
ON DELETE CASCADE
SQL Statements 1-165
CREATE TABLE
Element
column name
table name
Purpose
A referenced column or columns
in the referenced table. If the
referenced table is different from
the referencing table, the default
is the primary-key column or
columns. If the referenced table
is the same as the referencing
table, there is no default.
Restrictions
Syntax
You must observe restrictions on Identifier, p. 1-723
the table where the column
resides, the existing constraints
on the column, the data type of
the column, and the maximum
number of columns. See
“Restrictions on the Column
Name Variable in the REFERENCES Clause” below.
The name of the referenced table The referenced table can be the Table Name, p. 1-768
same table as the referencing
table, or it can be a different
table. The referenced table must
reside in the same database as
the referencing table.
Restrictions on the Column Name Variable in the REFERENCES Clause
You must observe the following restrictions on the column name variable.
Table Where the Column Resides
The referenced column (the column that you specify in the column name
variable) can be in the same table as the referencing column, or the referenced
column can be in a different table.
Existing Constraints on the Column
The referenced column must be a unique or primary-key column. That is, the
referenced column in the referenced table must already have a unique or
primary-key constraint placed on it.
Data Type of the Column
The data type of the referenced column must be identical to the data type of
the referencing column. The only exception is that a referencing column must
be INTEGER if the referenced column is SERIAL.
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CREATE TABLE
Number of Columns
You can specify only one column when you are using the REFERENCES clause
at the column level (that is, when you are using the REFERENCES clause in the
Column-Definition option).
You can specify multiple columns when you are using the REFERENCES
clause at the table level (that is, when you are using the REFERENCES clause
in the Constraint-Definition option).
The maximum number of columns and the total length of columns vary with
the database server, as the following list describes:
■
If you are using INFORMIX-OnLine Dynamic Server, the maximum
number of columns is 16, and the total length of the columns cannot
exceed 255 bytes.
■
If you are using INFORMIX-SE, the maximum number of columns is
8, and the total length of the columns cannot exceed 120 bytes.
Using the REFERENCES Clause
You can use the REFERENCES clause to establish a referential relationship
between two tables or within the same table.
The table referenced in the REFERENCES clause must reside in the same
database as the created table.
Referenced and Referencing Column Requirements
In a referential relationship, the referenced column is a column or set of
columns within a table that uniquely identifies each row in the table. In other
words, the referenced column or set of columns must be a unique or primarykey constraint. If the referenced columns do not meet this criteria, the
database server returns an error.
Unlike a referenced column, the referencing column or set of columns can
contain null and duplicate values. However, every non-null value in the
referencing columns must match a value in the referenced columns. When a
referencing column meets this criteria, it is called a foreign key.
SQL Statements 1-167
CREATE TABLE
The relationship between referenced and referencing columns is called a
parent-child relationship, where the parent is the referenced column (primary
key) and the child is the referencing column (foreign key). This parent-child
relationship is established through a referential constraint.
A referential constraint can be established between two tables or within the
same table. For example, you can have an employee table where the emp_no
column uniquely identifies every employee through an employee number.
The mgr_no column in that table contains the employee number of the
manager who manages that employee. In this case, mgr_no is the foreign key
(the child) that references emp_no, the primary key (the parent).
A referential constraint must have a one-to-one relationship between referencing and referenced columns. In other words, if the primary key is a set of
columns, then the foreign key also must be a set of columns that corresponds
to the primary key. The following example creates two tables. The first table
has a multiple-column primary key, and the second table has a referential
constraint that references this key.
CREATE TABLE accounts (
acc_num INTEGER,
acc_type INTEGER,
acc_descr CHAR(20),
PRIMARY KEY (acc_num, acc_type))
CREATE TABLE sub_accounts (
sub_acc INTEGER PRIMARY KEY,
ref_num INTEGER NOT NULL,
ref_type INTEGER NOT NULL,
sub_descr CHAR(20),
FOREIGN KEY (ref_num, ref_type) REFERENCES accounts
(acc_num, acc_type))
In this example, the foreign key of the sub_accounts table, ref_num and
ref_type, references the primary key, acc_num and acc_type, in the accounts
table. If, during an insert, you tried to insert a row into the sub_accounts
table whose value for ref_num and ref_type did not exactly correspond to
the values for acc_num and acc_type in an existing row in the accounts table,
the database server would return an error. Likewise, if you attempt to update
sub_accounts with values for ref_num and ref_type that do not correspond
to an equivalent set of values in acc_num and acc_type (from the accounts
table), the database server returns an error.
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CREATE TABLE
If you are referencing a primary key in another table, you do not have to state
the primary-key columns in that table explicitly. Referenced tables that do not
specify the referenced columns default to the primary-key columns. The
references section of the previous example can be rewritten, as the following
example shows:
.
.
.
FOREIGN KEY (ref_num, ref_type) REFERENCES accounts
.
.
.
Because acc_num and acc_type is the primary key of the accounts table, and
no other columns are specified, the foreign key, ref_num and ref_type,
references those columns.
Data Type Restrictions
The data types of the referencing and referenced columns must be identical
unless the column is SERIAL data type. You can specify SERIAL for the
primary key of the parent table and INTEGER for the foreign key. In the
previous example, a one-to-one correspondence exists between the data
types of the primary and foreign keys. If the primary-key column was
defined as type SERIAL, the statement would still be successfully executed.
You cannot place a referential constraint on a BYTE or TEXT column.
Locking Implications
When you create a referential constraint, an exclusive lock is placed on the
referenced table. The lock is released when the CREATE TABLE statement is
done. If you are creating a table in a database with transactions, and you are
using transactions, the lock is released at the end of the transaction.
SQL Statements 1-169
CREATE TABLE
Using REFERENCES in a Column Definition
When you use the REFERENCES clause at the column-definition level, you can
reference a single column. The following example creates two tables,
accounts and sub_accounts. A referential constraint is created between the
foreign key, ref_num, in the sub_accounts table and the primary key,
acc_num, in the accounts table.
CREATE TABLE accounts (
acc_num INTEGER PRIMARY KEY,
acc_type INTEGER,
acc_descr CHAR(20))
CREATE TABLE sub_accounts (
sub_acc INTEGER PRIMARY KEY,
ref_num INTEGER REFERENCES accounts (acc_num),
sub_descr CHAR(20))
Note that ref_num is not explicitly called a foreign key in the columndefinition syntax. At the column level, the foreign-key designation is applied
automatically.
If you are referencing the primary key in another table, you do not need to
specify the referenced table column. In the preceding example, you can
simply reference the accounts table without specifying a column. Because
acc_num is the primary key of the accounts table, it becomes the referenced
column by default.
Using the ON DELETE CASCADE Clause
Cascading deletes allow you to specify whether you want rows deleted in the
child table when rows are deleted in the parent table. Unless you specify
cascading deletes, the default prevents you from deleting data in the parent
table if child tables are associated with the parent table. With the ON DELETE
CASCADE clause, when you delete a row in the parent table, any rows
associated with that row (foreign keys) in a child table are also deleted. The
principal advantage to the cascading deletes feature is that it allows you to
reduce the quantity of SQL statements you need to perform delete actions.
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CREATE TABLE
For example, the all_candy table contains the candy_num column as a
primary key. The hard_candy table refers to the candy_num column as a
foreign key. The following CREATE TABLE statement creates the hard_candy
table with the cascading-delete clause on the foreign key:
CREATE TABLE hard_candy (candy_num INT, candy_flavor CHAR(20),
FOREIGN KEY (candy_num) REFERENCES all_candy ON DELETE CASCADE);
With cascading deletes specified on the child table, in addition to deleting a
candy item from the all_candy table, the delete cascades to the hard_candy
table associated with the candy_num foreign key.
You specify cascading deletes with the REFERENCES clause on a column-level
or table-level constraint. You need only the References privilege to indicate
cascading deletes. You do not need the Delete privilege to perform cascading
deletes; however, you do need the Delete privilege on tables referenced in the
DELETE statement. After you indicate cascading deletes, when you delete a
row from a parent table, OnLine deletes any associated matching rows from
the child table.
What Happens to Multiple Children Tables
If you have a parent table with two child constraints, one child with
cascading deletes specified and one child without cascading deletes, and you
attempt to delete a row from the parent table that applies to both child tables,
the delete statement fails, and no rows are deleted from either the parent or
child tables.
Locking and Logging
During deletes, the database server places locks on all qualifying rows of the
referenced and referencing tables. You must turn logging on when you
perform the deletes. If logging is turned off in a database, even temporarily,
deletes do not cascade. This restriction applies because if logging is turned
off, you cannot roll back any actions. For example, if a parent row is deleted,
and the system crashes before the child rows are deleted, the database will
have dangling child records, which violates referential integrity. However,
when logging is turned back on, subsequent deletes cascade.
SQL Statements 1-171
CREATE TABLE
Restriction on Cascading Deletes
Cascading deletes can be used for most deletes. The only exception is
correlated subqueries. In correlated subqueries, the subquery (or inner
SELECT) is correlated when the value it produces depends on a value
produced by the outer SELECT statement that contains it. If you have implemented cascading deletes, you cannot write deletes that use a child table in
the correlated subquery. You receive an error when you attempt to delete
from a query that contains such a correlated subquery.
See Chapter 4 of the Informix Guide to SQL: Tutorial for a detailed discussion
about cascading deletes.
The CHECK Clause
CHECK
Clause
CHECK
(
Condition
p. 1-643
)
Check constraints allow you to designate conditions that must be met before
data can be assigned to a column during an INSERT or UPDATE statement. If
a row evaluates to false for any check constraint defined on a table during an
insert or update, the database server returns an error.
Check constraints are defined using search conditions. The search condition
cannot contain subqueries; aggregates; host variables; rowids; the CURRENT,
USER, SITENAME, DBSERVERNAME, or TODAY functions; or stored procedure
calls.
Warning: When you specify a date value in a search condition, make sure to specify
4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on how the database server
interprets the search condition. When you specify a 2-digit year, the DBCENTURY
environment variable can affect how the database server interprets the search condition, so the check constraint might not work as you intended. See the “Informix
Guide to SQL: Reference” for more information on the DBCENTURY environment
variable.
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CREATE TABLE
Defining Check Constraints at the Column Level
If you define a check constraint at the column level, the only column that the
check constraint can check against is the column itself. In other words, the
check constraint cannot depend upon values in other columns of the table.
For example, as the following statement shows, the table acct_chk has two
columns with check constraints:
CREATE TABLE acct_chk (
chk_id SERIAL PRIMARY KEY,
debit INTEGER REFERENCES accounts (acc_num),
debit_amt MONEY CHECK (debit_amt BETWEEN 0 AND 99999),
credit INTEGER REFERENCES accounts (acc_num),
credit_amt MONEY CHECK (credit_amt BETWEEN 0 AND 99999))
Both debit_amt and credit_amt are columns of MONEY data type whose
values must be between 0 and 99999. If, however, you wanted to test that
both columns contained the same value, you would not be able to create the
check constraint at the column level. To create a constraint that checks values
in more than one column, you must define the constraint at the table level.
Defining Check Constraints at the Table Level
When a check constraint is defined at the table level, each column in the
search condition must be a column in that table. You cannot create a check
constraint for columns across tables. The next example builds the same table
and columns as the previous example. However, the check constraint now
spans two columns in the table.
CREATE TABLE acct_chk (
chk_id SERIAL PRIMARY KEY,
debit INTEGER REFERENCES accounts (acc_num),
debit_amt MONEY,
credit INTEGER REFERENCES accounts (acc_num),
credit_amt MONEY,
CHECK (debit_amt = credit_amt))
In this example, the debit_amt and credit_amt columns must equal each
other, or the insert or update fails.
SQL Statements 1-173
CREATE TABLE
Table-Level Constraint-Definition Option
Table-Level
Constraint Definition
,
(
UNIQUE
+
column
name
)
+
Constraint-Mode
Definitions
p. 1-163
DISTINCT
PRIMARY
KEY
,
FOREIGN KEY
column
name
(
)
REFERENCES
Clause
p. 1-165
CHECK
Clause
p. 1-172
Element
column name
Purpose
The name of the column or
columns on which the constraint
is placed
Restrictions
Syntax
You must observe general
Identifier, p. 1-723
restrictions that apply regardless
of the type of constraint you are
defining. You must also observe
specific restrictions that depend
on the type of constraint you are
defining. See “Restrictions on
the Column Name Variable in
the Table-Level ConstraintDefinition Option” below.
Restrictions on the Column Name Variable in the Table-Level
Constraint-Definition Option
You must observe the following restrictions on the column name variable:
1-174
■
General restrictions that apply regardless of the type of constraint
you are defining
■
Specific restrictions that depend on the type of constraint you are
defining
Informix Guide to SQL: Syntax
CREATE TABLE
General Restrictions
The column must be a column in the table, and the column cannot be a BYTE
or TEXT column.
The maximum number of columns and the total length of the columns vary
with the database server. If you are using INFORMIX-OnLine Dynamic Server,
you can include up to 16 columns in a list of columns. The total length of all
the columns cannot exceed 255 bytes. If you are using INFORMIX-SE, you can
use up to 8 columns in a list of columns. The total length of all the columns
cannot exceed 120 bytes.
Restrictions for Unique Constraints
When you define a unique constraint (UNIQUE or DISTINCT keywords), a
column cannot appear in the constraint list more than once.
You cannot place a unique constraint on a column on which you have already
placed a primary-key constraint.
Restrictions for Primary-Key Constraints
You can define a primary-key constraint (PRIMARY KEY keywords) on only
one column or one set of columns in a table.You cannot define a column or
set of columns as a primary key if you have already defined another column
or set of columns as the primary key.
Restrictions for Referential Constraints
When you specify a referential constraint, the data type of the referencing
column (the column you specify after the FOREIGN KEY keywords) must
match the data type of the referenced column (the column you specify in the
REFERENCES clause). The only exception is that the referencing column must
be INTEGER if the referenced column is SERIAL.
Using the Table-Level Constraint-Definition Option
The table-level constraint-definition option allows you to create constraints
for a single column or a set of columns. You can create the following types of
constraints with this option: unique, primary-key, foreign-key (referential),
and check constraints.
SQL Statements 1-175
CREATE TABLE
Defining a Column as Unique
Use the UNIQUE keyword to require that a single column or set of columns
accepts only unique data. You cannot insert duplicate values in a column that
has a unique constraint.
Each column named in a unique constraint must be a column in the table and
cannot appear in the constraint list more than once. The following example
creates a simple table that has a unique constraint on one of its columns:
CREATE TABLE accounts (a_name CHAR(12), a_code SERIAL,
UNIQUE (a_name) CONSTRAINT acc_name)
If you want to define the constraint at the column level instead, simply
include the keywords UNIQUE and CONSTRAINT in the column definition, as
the following example shows:
CREATE TABLE accounts
(a_name CHAR(12) UNIQUE CONSTRAINT acc_name, a_code SERIAL)
You cannot place a unique constraint on a BYTE or TEXT column.
Defining a Column as a Primary Key
A primary key is a column or set of columns that contains a non-null unique
value for each row in a table. A table can have only one primary key, and a
column that is defined as a primary key cannot also be defined as unique. In
the previous two examples, a unique constraint was placed on the column
a_name. The following example creates this column as the primary key for
the accounts table:
CREATE TABLE accounts
(a_name CHAR(12), a_code SERIAL, PRIMARY KEY (a_name))
You cannot place a primary-key constraint on a BYTE or TEXT column.
Defining a Column as a Foreign Key
A foreign key joins and establishes dependencies between tables. A foreign
key references a unique or primary key in a table. For every entry in the
foreign-key columns, a matching entry must exist in the unique or primarykey columns if all foreign-key columns contain non-null values. You cannot
make BYTE or TEXT columns foreign keys.
1-176
Informix Guide to SQL: Syntax
CREATE TABLE
TEMP TABLE Clause
Temp
Table
Clause
,
TEMP
TABLE
temp
table
name
(
Temporary
Table
Column
Definition
p. 1-180
Element
Purpose
temp table name The name that you want to
assign to the temporary table
)
,
,
WITH NO LOG
Temp Table
Table-Level
Constraint
p. 1-181
Restrictions
Syntax
The name must be different from Identifier, p. 1-723
any existing table, view, or
synonym name in the current
database, but it does not have to
be different from other
temporary table names used by
other users.
Temporary tables created with the CREATE TEMP TABLE statement are called
explicit temporary tables. Explicit temporary tables can also be created with
the SELECT ... INTO TEMP statement.
When an application creates an explicit temporary table, it exists until one of
the following situations occurs:
■
The application terminates.
■
The application closes the database where the table was created. In
this case, the table is dropped only if the database does transaction
logging, and the temporary table was not created with the WITH NO
LOG option.
■
The application closes the database where the table was created and
opens a database in a different database server (a second OnLine or
an SE database server).
When any of these events occur, the temporary table is deleted.
SQL Statements 1-177
CREATE TABLE
DB
The INFO statement and the Info Menu Option cannot be used with
temporary tables. ♦
Temporary table names must be different from existing table, view, or
synonym names in the current database; however, they need not be different
from other temporary table names used by other users.
Temporary tables that are created as a part of processing are called implicit
temporary tables. Implicit temporary tables are discussed in the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
You can specify where temporary tables are created with the CREATE TEMP
TABLE statement, environment variables, and ONCONFIG parameters.
OnLine stores temporary tables in the following order:
1.
The IN dbspace clause
You can specify the dbspace where you want the temporary table
stored with the IN dbspace clause of the CREATE TABLE statement.
2.
The dbspaces you specify when you fragment temporary tables
Use the FRAGMENT BY clause of the CREATE TABLE statement to
fragment regular and temporary tables.
3.
The DBSPACETEMP environment variable
If you do not use the IN dbspace clause or the FRAGMENT BY clause to
fragment the table, OnLine checks to see if the DBSPACETEMP
environment variable is set. The DBSPACETEMP environment
variable lists dbspaces where temporary tables can be stored. This
list can include standard dbspaces, temporary dbspaces, or both. If
the environment variable is set, OnLine stores the temporary table in
one of the dbspaces specified in that list.
4.
The ONCONFIG parameter DBSPACETEMP
You can specify a location for temporary tables with the ONCONFIG
parameter DBSPACETEMP.
If you do not use the IN dbspace clause, the FRAGMENT BY clause to fragment
the table, the DBSPACETEMP environment variable, or the ONCONFIG
parameter DBSPACETEMP, the temporary tables are created in the same
dbspace as your database server.
1-178
Informix Guide to SQL: Syntax
CREATE TABLE
You can specify more than one dbspace for the DBSPACETEMP environment
variable. For example, you can specify the following dbspace definitions for
the DBSPACETEMP environment variable:
setenv DBSPACETEMP tempspc1:tempspc2:tempspc3
Each temporary table that you create round-robins to a dbspace. For
example, if you created three temporary tables, the first one, temp1, would
go into the dbspace called tempspc1; the second one, temp2, would go into
tempspc2; and the third one, temp3, would go into tempspc3.
SE
Temporary tables are created in the directory specified by the DBTEMP
environment variable. If the DBTEMP environment variable is not set,
temporary tables are created in the directory of the database (that is, the
.dbs directory). ♦
For additional information about the DBSPACETEMP environment variable,
see Chapter 4, “Environment Variables” in the Informix Guide to SQL:
Reference. For additional information about the ONCONFIG parameter
DBSPACETEMP, see the INFORMIX-OnLine Dynamic Server Administrator’s
Guide.
If you have the Connect privilege on a database, you can create temporary
tables. Once a temporary table is created, you can build indexes on the table.
However, you are the only user who can see the temporary table.
Fragmenting Temporary Tables
You can create temporary tables with a fragmentation strategy.
SQL Statements 1-179
CREATE TABLE
Temporary-Table Column Definition
Temporary Table Column
Definition
column
name
Data Type
p. 1-664
DEFAULT
Clause
p. 1-159
Element
column name
Purpose
The name of a column in the
table
Temp Table
Column
Constraint
Definition
p. 1-180
NOT NULL
Restrictions
Name must be unique within a
table, but you can use the same
names in different tables in the
same database.
Syntax
Identifier, p. 1-723
You define columns for temporary tables in the same manner as you define
columns for regular database tables. The only difference is the option for
defining column constraints, which is defined in the following section.
For more information about defining single columns for temporary tables,
see the “Column-Definition Option” on page 1-158.
Temporary-Table Column Constraint Definition
Temp Table Column
Constraint Definition
UNIQUE
+
DISTINCT
PRIMARY
KEY
CHECK
Clause
p. 1-172
1-180
Informix Guide to SQL: Syntax
CREATE TABLE
Temporary-table column constraints are the same as column constraints for
regular tables, with the following exceptions:
■
You cannot place referential constraints on columns in a temporary
table. Temporary columns cannot be referenced or referencing
columns.
■
The Constraint Mode Definitions option is not available for columns
in temporary tables. You cannot assign a name to a constraint on a
temporary-table column. You cannot set the object mode of a
constraint on a temporary-table column. See “Constraint-Mode
Definitions” on page 1-163 for further information on this option.
For more information about column constraints in regular tables, see
“Column-Level Constraint-Definition Option” on page 1-162.
Table-Level Constraint for Temporary Tables
Temp Table Table-Level
Constraint
UNIQUE
,
(
+
column
name
)
DISTINCT
PRIMARY
KEY
CHECK
Clause
p. 1-172
Element
column name
Purpose
The name of the column or
columns on which the constraint
is placed
Restrictions
Syntax
See “Restrictions on Table-Level Identifier, p. 1-723
Constraints for Temporary
Tables” on page 1-182.
You can place a table-level constraint on one or more columns of a temporary
table.
SQL Statements 1-181
CREATE TABLE
Restrictions on Table-Level Constraints for Temporary Tables
Table-level constraints are defined for temporary tables in the same manner
as regular database tables, with the following exceptions:
■
You cannot place referential constraints on columns in a temporary
table. In other words, temporary columns cannot be referenced or
referencing columns.
■
The Constraint Mode Definitions option is not available for
constraints on columns in temporary tables. You cannot assign a
name to a constraint on a temporary-table column. You cannot set
the object mode of a constraint on a temporary-table column. See
“Constraint-Mode Definitions” on page 1-163 for further
information on this option.
For more information about table-level constraints on regular tables, see
“Table-Level Constraint-Definition Option” on page 1-174.
WITH NO LOG Option for Temporary Tables
You must use the WITH NO LOG keywords on temporary tables created in
temporary dbspaces.
Using the WITH NO LOG keywords prevents logging of temporary tables in
databases started with logging.
If you use the WITH NO LOG keywords in a CREATE TABLE statement, and the
database does not use logging, the WITH NO LOG option is ignored.
Once you turn off logging on a temporary table, you cannot turn it back on;
a temporary table is, therefore, always logged or never logged.
The following example shows how to prevent logging temporary tables in a
database that uses logging:
CREATE TEMP TABLE tab2 (fname CHAR(15), lname CHAR(15))
WITH NO LOG
1-182
Informix Guide to SQL: Syntax
CREATE TABLE
The WITH ROWIDS Clause
Important: Use the WITH ROWIDS clause only on fragmented tables. In nonfragmented tables, the rowid column remains unchanged. Informix recommends,
however, that you utilize primary keys as an access method rather than exploiting the
rowid column.
Nonfragmented tables contain a hidden column called the rowid column.
However, fragmented tables do not contain this column. If a table is
fragmented, you can use the WITH ROWIDS clause to add the rowid column
to the table. OnLine assigns each row in the rowid column a unique number
that remains stable for the life of the row. The database server uses an index
to find the physical location of the row. Each row contains an additional
4 bytes to store the rowid column after you add it.
Storage Option
Storage
Option
OL
IN dbspace
Extent Option
p. 1-188
LOCK MODE
p. 1-190
FRAGMENT
BY
Clause
p. 1-186
SE
IN 'pathname'
SQL Statements 1-183
CREATE TABLE
Element
dbspace
pathname
Purpose
The name of the dbspace in
which a database table or
temporary table is to be stored.
The default for database tables is
the dbspace in which the current
database resides.
The full operating-system
pathname and filename in which
you want to store the database
table. The default is the directory
of the database (the .dbs
directory).
Restrictions
Specified dbspace must already
exist.
Syntax
Identifier, p. 1-723
You cannot use the pathname
variable for a temporary table.
You can specify any valid
directory in pathname. You
cannot add an extension to the
filename.
See “The IN
pathname Option”
on page 1-190.
The storage option allows you to specify where the table is stored and the
locking granularity for the table.
The IN dbspace Clause
The IN dbspace clause allows you to isolate a table. The dbspace that you
specify must already exist. If you do not specify the IN dbspace clause, the
default is the dbspace where the current database resides. Temporary tables
do not have a default dbspace. For further information about storing
temporary tables, see the “TEMP TABLE Clause” on page 1-177.
1-184
Informix Guide to SQL: Syntax
CREATE TABLE
For example, if the stores7 database is in the stockdata dbspace, but you
want the customer data placed in a separate dbspace called custdata, use the
following statements:
CREATE DATABASE stores7 IN stockdata
CREATE TABLE customer
(
customer_num
SERIAL(101),
fname
CHAR(15),
lname
CHAR(15),
company
CHAR(20),
address1
CHAR(20),
address2
CHAR(20),
city
CHAR(15),
state
CHAR(2),
zipcode
CHAR(5),
phone
CHAR(18)
)
IN custdata EXTENT SIZE 16
.
.
.
For more information about storing your tables in separate dbspaces, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
If your table has one or more blob columns, you can store the blob data with
the table data or in a separate blobspace. See the Data Type segment on
page 1-664 for more information. The following example shows how
blobspaces and dbspaces are specified.
The following statement creates the resume table. The data for the table is
stored in the employ dbspace. The data in the resume column is stored with
the table, but the data associated with the photo column is stored in a
blobspace named photo_space.
CREATE TABLE resume
(
fname
lname
phone
recd_date
contact_date
comments
vita
photo
)
IN employ
CHAR(15),
CHAR(15),
CHAR(18),
DATETIME YEAR TO HOUR,
DATETIME YEAR TO HOUR,
VARCHAR(250, 100),
TEXT IN TABLE,
BYTE IN photo_space
SQL Statements 1-185
CREATE TABLE
The FRAGMENT BY Clause
The FRAGMENT BY clause allows you to create fragmented tables.
Fragmentation means that groups of rows within a table are stored together
in the same dbspace.
FRAGMENT BY
Clause
,
FRAGMENT BY
ROUND ROBIN IN
dbspace
,
dbspace
,
EXPRESSION
frag-expression
IN dbspace
,
frag-expression
IN dbspace
,
Element
dbspace
frag-expression
REMAINDER IN
remainder
dbspace
Purpose
Restrictions
The dbspace that contains a table You must specify at least two
fragment
dbspaces. You can specify a
maximum of 2,048 dbspaces.
The dbspaces must exist when
you execute the statement.
An expression that defines a
If you specify a value for
fragment where a row is to be
remainder dbspace, you must
stored using a range, hash, or
specify at least one fragment
arbitrary rule
expression. If you do not specify
a value for remainder dbspace, you
must specify at least two
fragment expressions. You can
specify a maximum of 2,048
fragment expressions. Each
fragment expression can contain
only columns from the current
table and only data values from
a single row. No subqueries,
stored procedures, current
date/time functions, or
aggregates are allowed in a
fragment expression.
Syntax
Identifier, p. 1-723
Expression, p. 1-671,
and Condition,
p. 1-643
(1 of 2)
1-186
Informix Guide to SQL: Syntax
CREATE TABLE
Element
remainder
dbspace
Purpose
The dbspace that contains table
rows that do not meet the conditions defined in any fragment
expression
Restrictions
Syntax
If you specify two or more
Identifier, p. 1-723
fragment expressions, remainder
dbspace is optional. If you specify
only one fragment expression,
remainder dbspace is required.
The dbspace specified in
remainder dbspace must exist at
the time you execute the
statement.
(2 of 2)
Use the FRAGMENT BY clause to define the distribution scheme, either roundrobin or expression-based.
In a round-robin distribution scheme, specify at least two dbspaces where
you want the fragments to be placed. As records are inserted into the table,
they are placed in the first available dbspace. OnLine balances the load
between the specified dbspaces as you insert records and distributes the rows
in such a way that the fragments always maintain approximately the same
number of rows. In this distribution scheme, the database server must scan
all fragments when searching for a row.
In an expression-based distribution scheme, each fragment expression in a rule
specifies a dbspace. Each fragment expression within the rule isolates data
and aids the database server in searching for rows. Specify one of the
following rules:
■
Range rule
A range rule specifies fragment expressions that use a range to
specify which rows are placed in a fragment, as the following
example shows:
...
FRAGMENT BY EXPRESSION
c1 < 100 IN dbsp1,
c1 >= 100 and c1 < 200 IN dbsp2,
c1 >= 200 IN dbsp3;
SQL Statements 1-187
CREATE TABLE
■
Hash rule
A hash rule specifies fragment expressions that are created when you
use a hash algorithm, which is often implemented with the MOD
function, as the following example shows:
...
FRAGMENT BY
MOD(id_num,
MOD(id_num,
MOD(id_num,
■
EXPRESSION
3) = 0 IN dbsp1,
3) = 1 IN dbsp2,
3) = 2 IN dbsp3;
Arbitrary rule
An arbitrary rule specifies fragment expressions based on a
predefined SQL expression that typically includes the use of OR
clauses to group data, as the following example shows:
...
FRAGMENT BY EXPRESSION
zip_num = 95228 OR zip_num = 95443 IN dbsp2,
zip_num = 91120 OR zip_num = 92310 IN dbsp4,
REMAINDER IN dbsp5;
Warning: When you specify a date value in a fragment expression, make sure to
specify 4 digits instead of 2 digits for the year. When you specify a 4-digit year, the
DBCENTURY environment variable has no effect on the distribution scheme. When
you specify a 2-digit year, the DBCENTURY environment variable can affect the distribution scheme and can produce unpredictable results. See the “Informix Guide to
SQL: Reference” for more information on the DBCENTURY environment variable.
Extent Option
Extent Option
EXTENT SIZE
1-188
Informix Guide to SQL: Syntax
first
kbytes
NEXT SIZE
next
kbytes
CREATE TABLE
Element
first kbytes
next kbytes
Purpose
The length in kilobytes of the
first extent for the table. The
default length is eight times the
disk page size on your system.
For example, if you have a
2-kilobyte page system, the
default length is 16 kilobytes.
The length in kilobytes for the
subsequent extents. The default
length is eight times the disk
page size on your system. For
example, if you have a 2-kilobyte
page system, the default length
is 16 kilobytes.
Restrictions
Syntax
The minimum length is four
Expression, p. 1-671
times the disk page size on your
system. For example, if you have
a 2-kilobyte page system, the
minimum length is eight
kilobytes. The maximum length
is equal to the chunk size.
The minimum length is four
Expression, p. 1-671
times the disk page size on your
system. For example, if you have
a 2-kilobyte page system, the
minimum length is
8 kilobytes.The maximum
length is equal to the chunk size.
See the INFORMIX-OnLine Dynamic Server Performance Guide for a discussion
about calculating extent sizes.
The following example specifies a first extent of 20 kilobytes and allows the
rest of the extents to use the default size:
CREATE TABLE emp_info
(
f_name CHAR(20),
l_name CHAR(20),
position CHAR(20),
start_date DATETIME YEAR TO DAY,
comments VARCHAR(255)
)
EXTENT SIZE 20
Revising Extent Sizes for Unloaded Tables
You can revise the CREATE TABLE statements in generated schema files to
revise the extent and next-extent sizes of unloaded tables. See the
INFORMIX-OnLine Dynamic Server Administrator’s Guide for information
about revising extent sizes.
SQL Statements 1-189
CREATE TABLE
LOCK MODE Clause
LOCK MODE Clause
LOCK MODE
PAGE
ROW
The default locking granularity is a page.
Row-level locking provides the highest level of concurrency. However, if you
are using many rows at one time, the lock-management overhead can
become significant. You can also exceed the maximum number of locks
available, depending on the configuration of your OnLine system.
Page locking allows you to obtain and release one lock on a whole page of
rows. Page locking is especially useful when you know that the rows are
grouped into pages in the same order that you are using to process all the
rows. For example, if you are processing the contents of a table in the same
order as its cluster index, page locking is especially appropriate.
You can change the lock mode of an existing table with the ALTER TABLE
statement.
The IN pathname Option
SE
The pathname in an IN clause can specify any valid directory and is not
restricted to the directory that contains the current database. This allows you
to spread your tables over multiple disks.
In UNIX, pathname cannot be longer than 64 characters and must be within
quotes ('). A pathname must appear in the following form:
[/directory-name/...]filename
If pathname in an IN clause specifies a filename that is different from table
name, always use table name (rather than the filename) to refer to the table in
subsequent <vk>SQL statements.
The creator of the table must have search permissions on all directories in the
path and write permissions on the directory that is to contain the files. ♦
1-190
Informix Guide to SQL: Syntax
CREATE TABLE
References
See the ALTER TABLE, CREATE INDEX, CREATE DATABASE, DROP TABLE, and
SET statements in this manual. Also see the Condition, Data Type, Identifier,
and Table Name segments.
In the Informix Guide to SQL: Tutorial, see the discussion of data-integrity
constraints and the discussion of the ON DELETE CASCADE clause in
Chapter 4. Also see the discussion of creating a database and tables in
Chapter 9.
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of extent sizing.
SQL Statements 1-191
CREATE TRIGGER
CREATE TRIGGER
Use the CREATE TRIGGER statement to create a trigger on a table in the
database. A trigger is a database object that automatically sets off a specified
set of SQL statements when a specified event occurs.
Syntax
DB
ESQL
+
CREATE TRIGGER
Trigger
Name
p. 1-195
Trigger Object
Modes
p. 1-222
INSERT
ON
Table
Name
p. 1-768
Action
Clause
p. 1-199
Insert
REFERENCING
Clause
p. 1-202
DELETE
ON
Table
Name
p. 1-768
Action
Clause
p. 1-199
Delete
REFERENCING
Clause
p. 1-203
UPDATE
Clause
p. 1-197
ON
Table
Name
p. 1-768
Informix Guide to SQL: Syntax
Action
Clause
Referencing
p. 1-205
Action
Clause
p. 1-199
Update
REFERENCING
Clause
p. 1-204
1-192
Action
Clause
Referencing
p. 1-205
Action
Clause
Referencing
p. 1-205
CREATE TRIGGER
Usage
You must be either the owner of the table or have the DBA status to create a
trigger on a table.
You can use roles with triggers. Role-related statements (CREATE ROLE,
DROP ROLE, and SET ROLE) and SET SESSION AUTHORIZATION statements
can be triggered inside a trigger. Privileges that a user has acquired through
enabling a role or through a SET SESSION AUTHORIZATION statement are not
relinquished when a trigger is executed.
You can define a trigger with a stand-alone CREATE TRIGGER statement.
DB
You can define a trigger as part of a schema by placing the CREATE TRIGGER
statement inside a CREATE SCHEMA statement. ♦
You can create a trigger only on a table in the current database. You cannot
create a trigger on a temporary table, a view, or a system catalog table.
You cannot create a trigger inside a stored procedure if the procedure is called
inside a data manipulation statement. For example, you cannot create a
trigger inside the stored procedure sp_items in the following INSERT
statement:
INSERT INTO items EXECUTE PROCEDURE sp_items
See “Data Manipulation Statements” on page 1-13 for a list of data
manipulation statements.
ESQL
If you are embedding the CREATE TRIGGER statement in an ESQL/C or
ESQL/COBOL program, you cannot use a host variable in the trigger
specification. ♦
You cannot use a stored procedure variable in a CREATE TRIGGER statement.
SE
You cannot use a ROLLBACK WORK statement to undo a CREATE TRIGGER
statement. If you roll back a transaction that contains a CREATE TRIGGER
statement, the trigger remains, and you do not receive an error message. ♦
SQL Statements 1-193
CREATE TRIGGER
The Trigger Event
The trigger event specifies the type of statement that activates a trigger. The
trigger event can be an INSERT, DELETE, or UPDATE statement. Each trigger
can have only one trigger event. The occurrence of the trigger event is the
triggering statement.
For each table, you can define only one trigger that is activated by an INSERT
statement and only one trigger that is activated by a DELETE statement. For
each table, you can define multiple triggers that are activated by UPDATE
statements. See “UPDATE Clause” on page 1-197 for more information about
multiple triggers on the same table.
You cannot define a DELETE trigger event on a table with a referential
constraint that specifies ON DELETE CASCADE.
You are responsible for guaranteeing that the triggering statement returns the
same result with and without the triggered actions. See “Action Clause” on
page 1-199 and “Triggered Action List” on page 1-206 for more information
on the behavior of triggered actions.
If INFORMIX-OnLine Dynamic Server is the database server, a triggering
statement from an external database server can activate the trigger. As shown
in the following example, an insert trigger on newtab, managed by
dbserver1, is activated by an INSERT statement from dbserver2. The trigger
executes as if the insert originated on dbserver1.
-- Trigger on stores7@dbserver1:newtab
CREATE TRIGGER ins_tr INSERT ON newtab
REFERENCING new AS post_ins
FOR EACH ROW(EXECUTE PROCEDURE nt_pct (post_ins.mc));
-- Triggering statement from dbserver2
INSERT INTO stores7@dbserver1:newtab
SELECT item_num, order_num, quantity, stock_num,
manu_code,
total_price FROM items;
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Informix Guide to SQL: Syntax
CREATE TRIGGER
Trigger Events with Cursors
If the triggering statement uses a cursor, the complete trigger is activated
each time the statement executes. For example, if you declare a cursor for a
triggering INSERT statement, each PUT statement executes the complete
trigger. Similarly, if a triggering UPDATE or DELETE statement contains the
clause WHERE CURRENT OF, each update or delete activates the complete
trigger. This behavior is different from what occurs when a triggering
statement does not use a cursor and updates multiple rows. In this case, the
set of triggered actions executes only once. For more information on the
execution of triggered actions, see “Action Clause” on page 1-199.
Privileges on the Trigger Event
You must have the appropriate Insert, Delete, or Update privilege on the
triggering table to execute the INSERT, DELETE, or UPDATE statement that is
the trigger event. The triggering statement might still fail, however, if you do
not have the privileges necessary to execute one of the SQL statements in the
action clause. When the triggered actions are executed, the database server
checks your privileges for each SQL statement in the trigger definition as if
the statement were being executed independently of the trigger. For information on the privileges you need to execute a trigger, see “Privileges to
Execute Triggered Actions” on page 1-215.
Impact of Triggers
The INSERT, DELETE, and UPDATE statements that initiate triggers might
appear to execute slowly because they activate additional SQL statements,
and the user might not know that other actions are occurring.
The execution time for a triggering data manipulation statement depends on
the complexity of the triggered action and whether it initiates other triggers.
Obviously, the elapsed time for the triggering data manipulation statement
increases as the number of cascading triggers increases. For more information on triggers that initiate other triggers, see “Cascading Triggers” on
page 1-216.
SQL Statements 1-195
CREATE TRIGGER
Trigger Name
Trigger
Name
Identifier
p. 1-723
owner.
Element
owner
Purpose
The user name of the owner of
the trigger
Restrictions
The specified name must be a
valid user name.
Syntax
Identifier, p. 1-723
When you create a trigger, the name of the trigger must be unique within a
database.
ANSI
When you create a trigger, the owner.name combination (the combination of
the owner name and trigger name) must be unique within a database. ♦
For information about the relationship between the trigger owner’s privileges and the privileges of other users, see “Privileges to Execute Triggered
Actions” on page 1-215.
1-196
Informix Guide to SQL: Syntax
CREATE TRIGGER
UPDATE Clause
UPDATE
Clause
UPDATE
,
OF
Element
column name
Purpose
The name of a column or
columns that activate the trigger.
The default is all the columns in
the table on which you create the
trigger.
column name
Restrictions
Syntax
The specified columns must
Identifier, p. 1-723
belong to the table on which you
create the trigger. If you define
more than one update trigger on
a table, the column lists of the
triggering statements must be
mutually exclusive.
If the trigger event is an UPDATE statement, the trigger executes when any
column in the triggering column list is updated.
If the triggering UPDATE statement updates more than one of the triggering
columns in a trigger, the trigger executes only once.
Defining Multiple Update Triggers
If you define more than one update trigger event on a table, the column lists
of the triggers must be mutually exclusive. The following example shows
that trig3 is illegal on the items table because its column list includes
stock_num, which is a triggering column in trig1. Multiple update triggers
on a table cannot include the same columns.
CREATE TRIGGER trig1 UPDATE OF item_num, stock_num ON items
REFERENCING OLD AS pre NEW AS post
FOR EACH ROW(EXECUTE PROCEDURE proc1());
CREATE TRIGGER trig2 UPDATE OF manu_code ON items
BEFORE(EXECUTE PROCEDURE proc2());
-- Illegal trigger: stock_num occurs in trig1
CREATE TRIGGER trig3 UPDATE OF order_num, stock_num ON items
BEFORE(EXECUTE PROCEDURE proc3());
SQL Statements 1-197
CREATE TRIGGER
When an UPDATE Statement Activates Multiple Triggers
When an UPDATE statement updates multiple columns that have different
triggers, the column numbers of the triggering columns determine the order
of trigger execution. Execution begins with the smallest triggering column
number and proceeds in order to the largest triggering column number. The
following example shows that table taba has four columns (a, b, c, d):
CREATE TABLE taba (a int, b int, c int, d int)
Define trig1 as an update on columns a and c, and define trig2 as an update
on columns b and d, as shown in the following example:
CREATE TRIGGER trig1 UPDATE OF a, c ON taba
AFTER (UPDATE tabb SET y = y + 1);
CREATE TRIGGER trig2 UPDATE OF b, d ON taba
AFTER (UPDATE tabb SET z = z + 1);
The triggering statement is shown in the following example:
UPDATE taba SET (b, c) = (b + 1, c + 1)
Then trig1 for columns a and c executes first, and trig2 for columns b and d
executes next. In this case, the smallest column number in the two triggers is
column 1 (a), and the next is column 2 (b).
1-198
Informix Guide to SQL: Syntax
CREATE TRIGGER
Action Clause
Action
Clause
BEFORE
Triggered
Action List
p. 1-206
FOR EACH
ROW
FOR EACH
ROW
Triggered
Action List
p. 1-206
Triggered
Action List
p. 1-206
AFTER
AFTER
AFTER
Triggered
Action List
p. 1-206
Triggered
Action List
p. 1-206
Triggered
Action List
p. 1-206
The action clause defines the characteristics of triggered actions and specifies
the time when these actions occur. You must define at least one triggered
action, using the keywords BEFORE, FOR EACH ROW, or AFTER to indicate
when the action occurs relative to the triggering statement. You can specify
triggered actions for all three options on a single trigger, but you must order
them in the following sequence: BEFORE, FOR EACH ROW, and AFTER. You
cannot follow a FOR EACH ROW triggered action list with a BEFORE triggered
action list. If the first triggered action list is FOR EACH ROW, an AFTER action
list is the only option that can follow it. See “Action Clause Referencing” on
page 1-205 for more information on the action clause when a REFERENCING
clause is present.
BEFORE Actions
The BEFORE triggered action or actions execute once before the triggering
statement executes. If the triggering statement does not process any rows, the
BEFORE triggered actions still execute because the database server does not
yet know whether any row is affected.
SQL Statements 1-199
CREATE TRIGGER
FOR EACH ROW Actions
The FOR EACH ROW triggered action or actions execute once for each row
that the triggering statement affects. The triggered SQL statement executes
after the triggering statement processes each row.
If the triggering statement does not insert, delete, or update any rows, the
FOR EACH ROW triggered actions do not execute.
AFTER Actions
An AFTER triggered action or actions execute once after the action of the
triggering statement is complete. If the triggering statement does not process
any rows, the AFTER triggered actions still execute.
Actions of Multiple Triggers
When an UPDATE statement activates multiple triggers, the triggered actions
merge. Assume that taba has columns a, b, c, and d, as shown in the
following example:
CREATE TABLE taba (a int, b int, c int, d int)
Next, assume that you define trig1 on columns a and c, and trig2 on columns
b and d. If both triggers have triggered actions that are executed BEFORE, FOR
EACH ROW, and AFTER, then the triggered actions are executed in the
following sequence:
1.
BEFORE action list for trigger (a, c)
2.
BEFORE action list for trigger (b, d)
3.
FOR EACH ROW action list for trigger (a, c)
4.
FOR EACH ROW action list for trigger (b, d)
5.
AFTER action list for trigger (a, c)
6.
AFTER action list for trigger (b, d)
The database server treats the triggers as a single trigger, and the triggered
action is the merged-action list. All the rules governing a triggered action
apply to the merged list as one list, and no distinction is made between the
two original triggers.
1-200
Informix Guide to SQL: Syntax
CREATE TRIGGER
Guaranteeing Row-Order Independence
In a FOR EACH ROW triggered-action list, the result might depend on the
order of the rows being processed. You can ensure that the result is
independent of row order by following these suggestions:
■
Avoid selecting the triggering table in the FOR EACH ROW section. If
the triggering statement affects multiple rows in the triggering table,
the result of the SELECT statement in the FOR EACH ROW section varies as each row is processed. This condition also applies to any
cascading triggers. See “Cascading Triggers” on page 1-216.
■
In the FOR EACH ROW section, avoid updating a table with values
derived from the current row of the triggering table. If the triggered
actions modify any row in the table more than once, the final result
for that row depends on the order in which rows from the triggering
table are processed.
■
Avoid modifying a table in the FOR EACH ROW section that is
selected by another triggered statement in the same FOR EACH ROW
section, including any cascading triggered actions. If you modify a
table in this section and refer to it later, the changes to the table might
not be complete when you refer to it. Consequently, the result might
differ, depending on the order in which rows are processed.
The database server does not enforce rules to prevent these situations
because doing so would restrict the set of tables from which a triggered
action can select. Furthermore, the result of most triggered actions is
independent of row order. Consequently, you are responsible for ensuring
that the results of the triggered actions are independent of row order.
SQL Statements 1-201
CREATE TRIGGER
INSERT REFERENCING Clause
INSERT
REFERENCING
Clause
REFERENCING
correlation name
NEW
AS
Element
correlation
name
Purpose
A name that you assign to a new
column value so that you can
refer to it within the triggered
action. The new column value in
the triggering table is the value
of the column after execution of
the triggering statement.
Restrictions
The correlation name must be
unique within the CREATE
TRIGGER statement.
Syntax
Identifier, p. 1-723
Once you assign a correlation name, you can use it only inside the FOR EACH
ROW triggered action. See “Action Clause Referencing” on page 1-205.
To use the correlation name, precede the column name with the correlation
name, followed by a period. For example, if the new correlation name is post,
refer to the new value for the column fname as post.fname.
If the trigger event is an INSERT statement, using the old correlation name as
a qualifier causes an error because no value exists before the row is inserted.
For the rules that govern the use of correlation names, see “Using Correlation
Names in Triggered Actions” on page 1-209.
You can use the INSERT REFERENCING clause only if you define a FOR EACH
ROW triggered action.
1-202
Informix Guide to SQL: Syntax
CREATE TRIGGER
The following example illustrates the use of the INSERT REFERENCING
clause. This example inserts a row into backup_table1 for every row that is
inserted into table1. The values that are inserted into col1 and col2 of
backup_table1 are an exact copy of the values that were just inserted into
table1.
CREATE TABLE table1 (col1 INT, col2 INT);
CREATE TABLE backup_table1 (col1 INT, col2 INT);
CREATE TRIGGER before_trig
INSERT ON table1
REFERENCING NEW as new
FOR EACH ROW
(
INSERT INTO backup_table1 (col1, col2)
VALUES (new.col1, new.col2)
);
As the preceding example shows, the advantage of the INSERT
REFERENCING clause is that it allows you to refer to the data values that the
trigger event in your triggered action produces.
DELETE REFERENCING Clause
DELETE
REFERENCING
Clause
REFERENCING
correlation name
OLD
AS
Element
correlation
name
Purpose
A name that you assign to an old
column value so that you can
refer to it within the triggered
action. The old column value in
the triggering table is the value
of the column before execution
of the triggering statement.
Restrictions
The correlation name must be
unique within the CREATE
TRIGGER statement.
Syntax
Identifier, p. 1-723
Once you assign a correlation name, you can use it only inside the FOR EACH
ROW triggered action. See “Action Clause Referencing” on page 1-205.
SQL Statements 1-203
CREATE TRIGGER
You use the correlation name to refer to an old column value by preceding the
column name with the correlation name and a period (.). For example, if the
old correlation name is pre, refer to the old value for the column fname as
pre.fname.
If the trigger event is a DELETE statement, using the new correlation name as
a qualifier causes an error because the column has no value after the row is
deleted. See “Using Correlation Names in Triggered Actions” on page 1-209
for the rules governing the use of correlation names.
You can use the DELETE REFERENCING clause only if you define a FOR EACH
ROW triggered action.
UPDATE REFERENCING Clause
UPDATE
REFERENCING
Clause
REFERENCING
1
correlation
name
OLD
AS
1
correlation
name
NEW
AS
Element
correlation
name
1-204
Purpose
A name that you assign to an old
or new column value so that you
can refer to it within the
triggered action. The old column
value in the triggering table is
the value of the column before
execution of the triggering
statement. The new column
value in the triggering table is
the value of the column after
executing the triggering
statement.
Informix Guide to SQL: Syntax
Restrictions
Syntax
You can specify a correlation
Identifier, p. 1-723
name for an old column value
only (OLD option), for a new
column value only (NEW
option), or for both the old and
new column values. Each correlation name you specify must be
unique within the CREATE
TRIGGER statement.
CREATE TRIGGER
Once you assign a correlation name, you can use it only inside the FOR EACH
ROW triggered action. See “Action Clause Referencing” on page 1-205.
Use the correlation name to refer to an old or new column value by preceding
the column name with the correlation name and a period (.). For example, if
the new correlation name is post, you refer to the new value for the column
fname as post.fname.
If the trigger event is an UPDATE statement, you can define both old and new
correlation names to refer to column values before and after the triggering
update. See “Using Correlation Names in Triggered Actions” on page 1-209
for the rules that govern the use of correlation names.
You can use the UPDATE REFERENCING clause only if you define a FOR EACH
ROW triggered action.
Action Clause Referencing
Action
Clause
Referencing
FOR EACH
ROW
BEFORE
Triggered
Action List
p. 1-206
Triggered
Action List
p. 1-206
AFTER
Triggered
Action List
p. 1-206
If the CREATE TRIGGER statement contains an INSERT REFERENCING clause,
a DELETE REFERENCING clause, or an UPDATE REFERENCING clause, you
must include a FOR EACH ROW triggered-action list in the action clause. You
can also include BEFORE and AFTER triggered-action lists, but they are
optional. See “Action Clause” on page 1-199 for information on the BEFORE,
FOR EACH ROW, and AFTER triggered-action lists.
SQL Statements 1-205
CREATE TRIGGER
Triggered Action List
Triggered
Action List
,
,
(
WHEN
(
Condition
p. 1-643
)
INSERT
Statement
p. 1-370
)
DELETE
Statement
p. 1-252
UPDATE
Statement
p. 1-612
EXECUTE
PROCEDURE
p. 1-293
The triggered action consists of an optional WHEN condition and the action
statements. Objects that are referenced in the triggered action, that is, tables,
columns, and stored procedures, must exist when the CREATE TRIGGER
statement is executed. This rule applies only to objects that are referenced
directly in the trigger definition.
Warning: When you specify a date expression in the WHEN condition or in an
action statement, make sure to specify 4 digits instead of 2 digits for the year. When
you specify a 4-digit year, the DBCENTURY environment variable has no effect on
how the database server interprets the date expression. When you specify a 2-digit
year, the DBCENTURY environment variable can affect how the database server
interprets the date expression, so the triggered action might produce unpredictable
results. See the “Informix Guide to SQL: Reference” for more information on the
DBCENTURY environment variable.
1-206
Informix Guide to SQL: Syntax
CREATE TRIGGER
The WHEN Condition
The WHEN condition lets you make the triggered action dependent on the
outcome of a test. When you include a WHEN condition in a triggered action,
if the triggered action evaluates to true, the actions in the triggered action list
execute in the order in which they appear. If the WHEN condition evaluates
to false or unknown, the actions in the triggered action list are not executed. If
the triggered action is in a FOR EACH ROW section, its search condition is
evaluated for each row.
For example, the triggered action in the following trigger executes only if the
condition in the WHEN clause is true:
CREATE TRIGGER up_price
UPDATE OF unit_price ON stock
REFERENCING OLD AS pre NEW AS post
FOR EACH ROW WHEN(post.unit_price > pre.unit_price * 2)
(INSERT INTO warn_tab VALUES(pre.stock_num,
pre.order_num, pre.unit_price, post.unit_price,
CURRENT))
A stored procedure that executes inside the WHEN condition carries the same
restrictions as a stored procedure that is called in a data manipulation
statement. See “CREATE PROCEDURE” on page 1-134 for more information
about a stored procedure that is called within a data manipulation statement.
The Action Statements
The triggered-action statements can be INSERT, DELETE, UPDATE, or
EXECUTE PROCEDURE statements. If a triggered-action list contains multiple
statements, these statements execute in the order in which they appear in the
list.
SE
In INFORMIX-SE, all objects referenced in the triggered actions must be in the
current database. ♦
SQL Statements 1-207
CREATE TRIGGER
Achieving a Consistent Result
To guarantee that the triggering statement returns the same result with and
without the triggered actions, make sure that the triggered actions in the
BEFORE and FOR EACH ROW sections do not modify any table referenced in
the following clauses:
■
WHERE clause
■
SET clause in the UPDATE statement
■
SELECT clause
■
EXECUTE PROCEDURE clause in a multiple-row INSERT statement
Using Keywords
If you use the INSERT, DELETE, UPDATE, or EXECUTE keywords as an
identifier in any of the following clauses inside a triggered action list, you
must qualify them by the owner name, the table name, or both:
■
FROM clause of a SELECT statement
■
INTO clause of the EXECUTE PROCEDURE statement
■
GROUP BY clause
■
SET clause of the UPDATE statement
You get a syntax error if these keywords are not qualified when you use these
clauses inside a triggered action.
If you use the keyword as a column name, it must be qualified by the table
name—for example, table.update. If both the table name and the column
name are keywords, they must be qualified by the owner name—for
example, owner.insert.update. If the owner name, table name, and column
name are all keywords, the owner name must be in quotes—for example,
'delete'.insert.update. The only exception is when these keywords are the
first table or column name in the list, and you do not have to qualify them.
For example, delete in the following statement does not need to be qualified
because it is the first column listed in the INTO clause:
CREATE TRIGGER t1 UPDATE OF b ON tab1
FOR EACH ROW (EXECUTE PROCEDURE p2()
INTO delete, d)
1-208
Informix Guide to SQL: Syntax
CREATE TRIGGER
The following statements show examples in which you must qualify the
column name or the table name:
FROM clause of a SELECT statement
CREATE TRIGGER t1 INSERT ON tab1
BEFORE (INSERT INTO tab2 SELECT * FROM tab3,
'owner1'.update)
INTO clause of an EXECUTE PROCEDURE statement
CREATE TRIGGER t3 UPDATE OF b ON tab1
FOR EACH ROW (EXECUTE PROCEDURE p2() INTO
d, tab1.delete)
GROUP BY clause of a SELECT statement
CREATE TRIGGER t4 DELETE ON tab1
BEFORE (INSERT INTO tab3 SELECT deptno, SUM(exp)
FROM budget GROUP BY deptno, budget.update)
SET clause of an UPDATE statement
CREATE TRIGGER t2 UPDATE OF a ON tab1
BEFORE (UPDATE tab2 SET a = 10, tab2.insert = 5)
Using Correlation Names in Triggered Actions
The following rules apply when you use correlation names in triggered
actions:
■
You can use the correlation names for the old and new column values
only in statements in the FOR EACH ROW triggered-action list. You
can use the old and new correlation names to qualify any column in
the triggering table in either the WHEN condition or the triggered
SQL statements.
■
The old and new correlation names refer to all rows affected by the
triggering statement.
SQL Statements 1-209
CREATE TRIGGER
■
You cannot use the correlation name to qualify a column name in the
GROUP BY, the SET, or the COUNT DISTINCT clause.
■
The scope of the correlation names is the entire trigger definition.
This scope is statically determined, meaning that it is limited to the
trigger definition; it does not encompass cascading triggers or
columns that are qualified by a table name in a stored procedure that
is a triggered action.
When to Use Correlation Names
In an SQL statement in a FOR EACH ROW triggered action, you must qualify
all references to columns in the triggering table with either the old or new
correlation name, unless the statement is valid independent of the triggered
action.
In other words, if a column name inside a FOR EACH ROW triggered action
list is not qualified by a correlation name, even if it is qualified by the
triggering table name, it is interpreted as if the statement is independent of
the triggered action. No special effort is made to search the definition of the
triggering table for the nonqualified column name.
For example, assume that the following DELETE statement is a triggered
action inside the FOR EACH ROW section of a trigger:
DELETE FROM tab1 WHERE col_c = col_c2
For the statement to be valid, both col_c and col_c2 must be columns from
tab1. If col_c2 is intended to be a correlation reference to a column in the
triggering table, it must be qualified by either the old or the new correlation
name. If col_c2 is not a column in tab1 and is not qualified by either the old
or new correlation name, you get an error.
1-210
Informix Guide to SQL: Syntax
CREATE TRIGGER
When a column is not qualified by a correlation name, and the statement is
valid independent of the triggered action, the column name refers to the
current value in the database. In the triggered action for trigger t1 in the
following example, mgr in the WHERE clause of the correlated subquery is an
unqualified column from the triggering table. In this case, mgr refers to the
current column value in empsal because the INSERT statement is valid
independent of the triggered action.
CREATE
CREATE
CREATE
CREATE
DATABASE db1;
TABLE empsal (empno INT, salary INT, mgr INT);
TABLE mgr (eno INT, bonus INT);
TABLE biggap (empno INT, salary INT, mgr INT);
CREATE TRIGGER t1 UPDATE OF salary ON empsal
AFTER (INSERT INTO biggap SELECT * FROM empsal WHERE salary <
(SELECT bonus FROM mgr WHERE eno = mgr));
In a triggered action, an unqualified column name from the triggering table
refers to the current column value, but only when the triggered statement is
valid independent of the triggered action.
Qualified Versus Unqualified Value
The following table summarizes the value retrieved when you use the
column name qualified by the old correlation name and the column name
qualified by the new correlation name.
Trigger Event
old.col
new.col
INSERT
no value (error)
inserted value
UPDATE
original value
current value (N)
original value
current value (U)
original value
no value (error)
(column updated)
UPDATE
(column not updated)
DELETE
SQL Statements 1-211
CREATE TRIGGER
Refer to the following key when you read the table.
Term
Meaning
original value
is the value before the triggering statement.
current value
is the value after the triggering statement.
(N)
cannot be changed by triggered action.
(U)
can be updated by triggered statements; value may be
different from original value because of preceding triggered
actions.
Outside a FOR EACH ROW triggered-action list, you cannot qualify a column
from the triggering table with either the old correlation name or the new
correlation name; it always refers to the current value in the database.
Action on the Triggering Table
You cannot reference the triggering table in any triggered SQL statement,
with the following exceptions:
■
The trigger event is UPDATE and the triggered SQL statement is also
UPDATE, and the columns in both statements, including any
nontriggering columns in the triggering UPDATE, are mutually
exclusive.
For example, assume that the following UPDATE statement, which
updates columns a and b of tab1, is the triggering statement:
UPDATE tab1 SET (a, b) = (a + 1, b + 1)
Now consider the triggered actions in the following example. The
first UPDATE statement is a valid triggered action, but the second one
is not because it updates column b again.
UPDATE tab1 SET c = c + 1; -- OK
UPDATE tab1 SET b = b + 1;-- ILLEGAL
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Informix Guide to SQL: Syntax
CREATE TRIGGER
■
The triggered SQL statement is a SELECT statement. The SELECT
statement can be a triggered statement in the following instances:
❑
The SELECT statement appears in a subquery in the WHEN clause
or a triggered-action statement.
❑
The triggered action is a stored procedure, and the SELECT
statement appears inside the stored procedure.
This rule, which states that a triggered SQL statement cannot reference the
triggering table, with the two noted exceptions, applies recursively to all
cascading triggers, which are considered part of the initial trigger. This
situation means that a cascading trigger cannot update any columns in the
triggering table that were updated by the original triggering statement,
including any nontriggering columns affected by that statement. For
example, assume the following UPDATE statement is the triggering
statement:
UPDATE tab1 SET (a, b) = (a + 1, b + 1)
Then in the cascading triggers shown in the following example, trig2 fails at
runtime because it references column b, which is updated by the triggering
UPDATE statement. See “Cascading Triggers” on page 1-216 for more
information about cascading triggers.
CREATE TRIGGER trig1 UPDATE OF a ON tab1-- Valid
AFTER (UPDATE tab2 set e = e + 1);
CREATE TRIGGER trig2 UPDATE of e ON tab2-- Invalid
AFTER (UPDATE tab1 set b = b + 1);
SQL Statements 1-213
CREATE TRIGGER
Rules for Stored Procedures
The following rules apply to a stored procedure that is used as a triggered
action:
■
The stored procedure cannot be a cursory procedure (that is, a
procedure that returns more than one row) in a place where only one
row is expected.
■
When an EXECUTE PROCEDURE statement is the triggered action,
you can specify the INTO clause only for an UPDATE trigger when the
triggered action occurs in the FOR EACH ROW section. In this case,
the INTO clause can contain only column names from the triggering
table. The following statement illustrates the appropriate use of the
INTO clause:
CREATE TRIGGER upd_totpr UPDATE OF quantity ON items
REFERENCING OLD AS pre_upd NEW AS post_upd
FOR EACH ROW(EXECUTE PROCEDURE
calc_totpr(pre_upd.quantity,
post_upd.quantity, pre_upd.total_price)
INTO total_price)
When the INTO clause appears in the EXECUTE PROCEDURE
statement, the database server updates the columns named there
with the values returned from the stored procedure. The database
server performs the update immediately upon returning from the
stored procedure. See “EXECUTE PROCEDURE” on page 1-293 for
more information about the statement.
■
You cannot use the old or new correlation name inside the stored
procedure. If you need to use the corresponding values in the
procedure, you must pass them as parameters. The stored procedure
should be independent of triggers, and the old or new correlation
name do not have any meaning outside the trigger.
■
You cannot use the following statements inside the stored procedure:
ALTER FRAGMENT, ALTER INDEX, ALTER OPTICAL, ALTER TABLE,
BEGIN WORK, COMMIT WORK, CREATE TRIGGER, DELETE, DROP
INDEX, DROP OPTICAL, DROP SYNONYM, DROP TABLE, DROP
TRIGGER, DROP VIEW, INSERT, RENAME COLUMN, RENAME TABLE,
ROLLBACK WORK, SET CONSTRAINTS, and UPDATE.
When you use a stored procedure as a triggered action, the objects that it
references are not checked until the procedure is executed.
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Informix Guide to SQL: Syntax
CREATE TRIGGER
Privileges to Execute Triggered Actions
If you are not the trigger owner but the trigger owner’s privileges include the
WITH GRANT OPTION privilege, you inherit the owner’s privileges as well as
the WITH GRANT OPTION privilege for each triggered SQL statement. You
have these privileges in addition to your privileges.
If the triggered action is a stored procedure, you must have the Execute
privilege on the procedure or the owner of the trigger must have the Execute
privilege and the WITH GRANT OPTION privilege. Inside the stored
procedure, you do not carry the privileges of the trigger owner; instead you
have the following privileges:
1.
The triggered action is a DBA-privileged procedure.
When you are granted the Execute privilege on the procedure, the
database server automatically grants you DBA privileges for the
procedure execution. These DBA privileges are available only when
you are executing the procedure.
2.
The triggered action is an owner-privileged procedure.
If the procedure owner has the WITH GRANT OPTION right for the
necessary privileges on the underlying objects, you inherit these
privilege when you are granted the Execute privilege. In this case, all
the nonqualified objects that the procedure references are qualified
by the name of the procedure owner.
If the procedure owner does not have the WITH GRANT OPTION
right, you have your original privileges on the underlying objects
when the procedure executes.
For more information on privileges on stored procedures, see Chapter 12 in
the Informix Guide to SQL: Tutorial.
SQL Statements 1-215
CREATE TRIGGER
Creating a Triggered Action That Anyone Can Use
To create a trigger that is executable by anyone who has the privileges to
execute the triggering statement, you can ask the DBA to create a
DBA-privileged procedure and grant you the Execute privilege with the
WITH GRANT OPTION right. You then use the DBA-privileged procedure as
the triggered action. Anyone can execute the triggered action because the
DBA-privileged procedure carries the WITH GRANT OPTION right. When you
activate the procedure, the database server applies privilege-checking rules
for a DBA. For more information about privileges on stored procedures, see
Chapter 12 of the Informix Guide to SQL: Tutorial.
Cascading Triggers
The database server allows triggers to cascade, meaning that the triggered
actions of one trigger can activate another trigger. The maximum number of
triggers in a cascading sequence is 61; the initial trigger plus a maximum of
60 cascading triggers. When the number of cascading triggers in a series
exceeds the maximum, the database server returns error number -748, as the
following example shows:
Exceeded limit on maximum number of cascaded triggers.
The following example illustrates a series of cascading triggers that enforce
referential integrity on the manufact, stock, and items tables in the stores7
database. When a manufacturer is deleted from the manufact table, the first
trigger, del_manu, deletes all the items from that manufacturer from the
stock table. Each delete in the stock table activates a second trigger,
del_items, that deletes all the items from that manufacturer from the items
table. Finally, each delete in the items table triggers the stored procedure
log_order, which creates a record of any orders in the orders table that can no
longer be filled.
CREATE TRIGGER del_manu
DELETE ON manufact
REFERENCING OLD AS pre_del
FOR EACH ROW(DELETE FROM stock
WHERE manu_code = pre_del.manu_code);
CREATE TRIGGER del_stock
DELETE ON stock
REFERENCING OLD AS pre_del
FOR EACH ROW(DELETE FROM items
1-216
Informix Guide to SQL: Syntax
CREATE TRIGGER
WHERE manu_code = pre_del.manu_code);
CREATE TRIGGER del_items
DELETE ON items
REFERENCING OLD AS pre_del
FOR EACH ROW(EXECUTE PROCEDURE log_order(pre_del.order_num));
When you are not using logging, or you are using the INFORMIX-SE database
server, with or without logging, referential integrity constraints on both the
manufact and stock tables would prohibit the triggers in this example from
executing. When you use INFORMIX-OnLine Dynamic Server with logging,
however, the triggers execute successfully because constraint checking is
deferred until all the triggered actions are complete, including the actions of
cascading triggers. See “Constraint Checking” on page 1-217 for more information about how constraints are handled when triggers execute.
The database server prevents loops of cascading triggers by not allowing you
to modify the triggering table in any cascading triggered action, except an
UPDATE statement, which does not modify any column that the triggering
UPDATE statement updated.
Constraint Checking
When you use logging, INFORMIX-OnLine Dynamic Server defers constraint
checking on the triggering statement until after the statements in the
triggered-action list execute. OnLine effectively executes a SET statement
(SET CONSTRAINTS ALL DEFERRED) before it executes the triggering
statement. After the triggered action is completed, it effectively executes
another SET statement (SET CONSTRAINTS constr_name IMMEDIATE) to check
the constraints that were deferred. This action allows you to write triggers so
that the triggered action can resolve any constraint violations that the
triggering statement creates. For more information, see the SET statement on
page 1-501.
SQL Statements 1-217
CREATE TRIGGER
Consider the following example, in which the table child has constraint r1,
which references the table parent. You define trigger trig1 and activate it with
an INSERT statement. In the triggered action, trig1 checks to see if parent has
a row with the value of the current cola in child; if not, it inserts it.
CREATE TABLE parent (cola INT PRIMARY KEY);
CREATE TABLE child (cola INT REFERENCES parent CONSTRAINT r1);
CREATE TRIGGER trig1 INSERT ON child
REFERENCING NEW AS new
FOR EACH ROW
WHEN((SELECT COUNT (*) FROM parent
WHERE cola = new.cola) = 0)
-- parent row does not exist
(INSERT INTO parent VALUES (new.cola));
When you insert a row into a table that is the child table in a referential
constraint, the row might not exist in the parent table. The database server
does not immediately return this error on a triggering statement. Instead, it
allows the triggered action to resolve the constraint violation by inserting the
corresponding row into the parent table. As the previous example shows,
you can check within the triggered action to see whether the parent row
exists, and if so, bypass the insert.
For an INFORMIX-OnLine Dynamic Server database without logging, OnLine
does not defer constraint checking on the triggering statement. In this case, it
immediately returns an error if the triggering statement violates a constraint.
OnLine does not allow the SET statement in a triggered action. OnLine checks
this restriction when you activate a trigger because the statement could occur
inside a stored procedure.
SE
1-218
For an INFORMIX-SE database, with or without logging, constraint checking
occurs prior to the triggered action. If a constraint violation results from the
triggering statement, INFORMIX-SE returns an error immediately. ♦
Informix Guide to SQL: Syntax
CREATE TRIGGER
Preventing Triggers from Overriding Each Other
When you activate multiple triggers with an UPDATE statement, a trigger can
possibly override the changes that an earlier trigger made. If you do not want
the triggered actions to interact, you can split the UPDATE statement into
multiple UPDATE statements, each of which updates an individual column.
As another alternative, you can create a single update trigger for all columns
that require a triggered action. Then, inside the triggered action, you can test
for the column being updated and apply the actions in the desired order. This
approach, however, is different than having the database server apply the
actions of individual triggers, and it has the following disadvantages:
■
If the trigger has a BEFORE action, it applies to all columns because
you cannot yet detect whether a column has changed.
■
If the triggering UPDATE statement sets a column to the current
value, you cannot detect the update, so the triggered action is
skipped. You might want to execute the triggered action even though
the value of the column has not changed.
The Client/Server Environment
In an OnLine database, the statements inside the triggered action can affect
tables in external databases. The following example shows an update trigger
on dbserver1, which triggers an update to items on dbserver2:
CREATE TRIGGER upd_nt UPDATE ON newtab
REFERENCING new AS post
FOR EACH ROW(UPDATE stores7@dbserver2:items
SET quantity = post.qty WHERE stock_num = post.stock
AND manu_code = post.mc)
SQL Statements 1-219
CREATE TRIGGER
If a statement from an external database server initiates the trigger, however,
and the triggered action affects tables in an external database, the triggered
actions fail. For example, the following combination of triggered action and
triggering statement results in an error when the triggering statement
executes:
-- Triggered action from dbserver1 to dbserver3:
CREATE TRIGGER upd_nt UPDATE ON newtab
REFERENCING new AS post
FOR EACH ROW(UPDATE stores7@dbserver3:items
SET quantity = post.qty WHERE stock_num = post.stock
AND manu_code = post.mc);
-- Triggering statement from dbserver2:
UPDATE stores7@dbserver1:newtab
SET qty = qty * 2 WHERE s_num = 5
AND mc = 'ANZ';
SE
In an INFORMIX-SE database, all objects referenced in the triggered actions
must be in the current database. ♦
Logging and Recovery
You can create triggers for databases, with and without logging. However,
when the database does not have logging, you cannot roll back when the
triggering statement fails. In this case, you are responsible for maintaining
data integrity in the database.
In INFORMIX-OnLine Dynamic Server, if the trigger fails and the database has
transactions, all triggered actions and the triggering statement are rolled back
because the triggered actions are an extension of the triggering statement.
The rest of the transaction, however, is not rolled back.
SE
In INFORMIX-SE, if you explicitly begin a transaction, you must explicitly roll
back the whole transaction. If the database has no transactions, data integrity
might possibly be violated when the triggered actions fail.
Even if the database has logging, any data definition statement in the
triggered action cannot be rolled back. Again, you are responsible for
maintaining data integrity as well as integrity of the database structure. ♦
1-220
Informix Guide to SQL: Syntax
CREATE TRIGGER
The row action of the triggering statement occurs before the triggered actions
in the FOR EACH ROW section. If the triggered action fails for a database
without logging, the application must restore the row that was changed by
the triggering statement to its previous value.
When you use a stored procedure as a triggered action, if you terminate the
procedure in an exception-handling section, any actions that modify data
inside that section are rolled back along with the triggering statement. In the
following partial example, when the exception handler traps an error, it
inserts a row into the table logtab:
ON EXCEPTION IN (-201)
INSERT INTO logtab values (errno, errstr);
RAISE EXCEPTION -201
END EXCEPTION
When the RAISE EXCEPTION statement returns the error, however, the
database server rolls back this insert because it is part of the triggered actions.
If the procedure is executed outside a triggered action, the insert is not rolled
back.
The stored procedure that implements a triggered action cannot contain any
BEGIN WORK, COMMIT WORK, or ROLLBACK WORK statements. If the
database has logging, you must either begin an explicit transaction before the
triggering statement, or the statement itself must be an implicit transaction.
In any case, another transaction-related statement cannot appear inside the
stored procedure.
You can use triggers to enforce referential actions that the database server
does not currently support. For any INFORMIX-SE database or for an
INFORMIX-OnLine Dynamic Server database without logging, you are
responsible for maintaining data integrity when the triggering statement
fails.
SQL Statements 1-221
CREATE TRIGGER
Trigger Object Modes
Trigger Object
Modes
DISABLED
ENABLED
The Trigger Object Modes option allows you to create a trigger in either the
enabled or disabled object mode.
You can create triggers in the following object modes.
Object Mode
Effect
disabled
When a trigger is created in disabled mode, the database server
does not execute the triggered action when the trigger event (an
insert, delete, or update operation) takes place. In effect, the
database server ignores the trigger even though its catalog
information is maintained.
enabled
When a trigger is created in enabled mode, the database server
executes the triggered action when the trigger event (an insert,
delete, or update operation) takes place.
Specifying Object Modes for Triggers
You must observe the following rules when you specify the object mode for
a trigger in the CREATE TRIGGER statement:
1-222
■
If you do not specify the disabled or enabled object modes explicitly,
the default object mode is enabled.
■
In contrast to unique indexes and constraints of all types, you cannot
set triggers to the filtering object mode because a trigger does not
impose any type of data-integrity requirement on the tables in the
database.
Informix Guide to SQL: Syntax
CREATE TRIGGER
■
You can use the SET statement to switch the mode of a disabled
trigger to the enabled mode. Once the trigger has been re-enabled,
the database server executes the triggered action whenever the
trigger event takes place. However, the re-enabled trigger does not
perform retroactively. The database server does not attempt to
execute the trigger for rows that were inserted, deleted, or updated
after the trigger was disabled and before it was enabled; therefore, be
cautious about disabling a trigger. If disabling a trigger will
eventually destroy the semantic integrity of the database, do not
disable the trigger in the first place.
■
You cannot create a trigger on a violations table or a diagnostics
table.
References
See the DROP TRIGGER, CREATE PROCEDURE, and EXECUTE PROCEDURE
statements in this manual.
In the Informix Guide to SQL: Tutorial, see Chapter 12.
SQL Statements 1-223
CREATE VIEW
CREATE VIEW
Use the CREATE VIEW statement to create a new view that is based upon
existing tables and views in the database.
Syntax
CREATE VIEW
View
Name
p. 1-772
,
(
Element
column name
AS
Purpose
The name of a column or
columns in the view
column
name
)
SELECT
Statement
(Subset)
p. 1-225
WITH CHECK
OPTION
Restrictions
Syntax
See “Naming View Columns” on Identifier, p. 1-723
page 1-226.
Usage
Except for the statements in the following list, you can use a view in any
<vk>SQL statement where you can use a table.
ALTER FRAGMENT
ALTER INDEX
ALTER TABLE
CREATE INDEX
CREATE TABLE
CREATE TRIGGER
DROP TABLE
DROP TRIGGER
LOCK TABLE
RECOVER TABLE
RENAME TABLE
UNLOCK TABLE
DROP INDEX
The view behaves like a table that is called view name. It consists of the set of
rows and columns that the SELECT statement returns each time the SELECT
statement is executed by using the view. The view reflects changes to the
underlying tables with one exception. If a SELECT * clause defines the view,
the view has only the columns in the underlying tables at the time the view
is created. New columns that are subsequently added to the underlying
tables with the ALTER TABLE statement do not appear in the view.
1-224
Informix Guide to SQL: Syntax
CREATE VIEW
The view name must be unique; that is, a view name cannot have the same
name as another database object, such as a table, synonym, or temporary
table.
The view inherits the data types of the columns from the tables from which
they come. Data types of virtual columns are determined from the nature of
the expression.
To create a view, you must have the Select privilege on all columns from
which the view is derived.
The SELECT statement is stored in the sysviews system catalog table. When
you subsequently refer to a view in another statement, the database server
performs the defining SELECT statement while it executes the new statement.
SE
DB
You cannot use a ROLLBACK WORK statement to undo a CREATE VIEW
statement. If you roll back a transaction that contains a CREATE VIEW
statement, the view remains, and you do not receive an error message. ♦
If you create a view outside the CREATE SCHEMA statement, you receive
warnings if you use the -ansi flag or set DBANSIWARN. ♦
Subset of a SELECT Allowed in CREATE VIEW
The SELECT statement has the form that is described on page 1-459, but in
CREATE VIEW, it cannot have an ORDER BY clause, INTO TEMP clause, or
UNION operator. Do not use display labels in the select list; display labels are
interpreted as column names.
SQL Statements 1-225
CREATE VIEW
Naming View Columns
The number of columns that you specify in the column name parameter must
match the number of columns returned by the SELECT statement that defines
the view.
If you do not specify a list of columns, the view inherits the column names of
the underlying tables. In the following example, the view herostock has the
same column names as the ones in the SELECT statement:
CREATE VIEW herostock AS
SELECT stock_num, description, unit_price, unit, unit_descr
FROM stock WHERE manu_code = 'HRO'
If the SELECT statement returns an expression, the corresponding column in
the view is called a virtual column. You must provide a name for virtual
columns. You must also provide a column name in cases where the selected
columns have duplicate column names when the table prefixes are stripped.
For example, when both orders.order_num and items.order_num appear in
the SELECT statement, you must provide two separate column names to label
them in the CREATE VIEW statement, as the following example shows:
CREATE VIEW someorders (custnum,ocustnum,newprice) AS
SELECT orders.order_num,items.order_num,
items.total_price*1.5
FROM orders, items
WHERE orders.order_num = items.order_num
AND items.total_price > 100.00
If you must provide names for some of the columns in a view, then you must
provide names for all the columns; that is, the column list must contain an
entry for every column that appears in the view.
Using a View in the SELECT Statement
You can define a view in terms of other views, but you must abide by the
restrictions on creating views that are listed in Chapter 10 of the Informix
Guide to SQL: Tutorial. See that manual for further information.
1-226
Informix Guide to SQL: Syntax
CREATE VIEW
WITH CHECK OPTION Keywords
The WITH CHECK OPTION keywords instruct the database server to ensure
that all modifications that are made through the view to the underlying tables
satisfy the definition of the view.
The following example creates a view that is named palo_alto, which uses all
the information in the customer table for customers in the city of Palo Alto.
The database server checks any modifications made to the customer table
through palo_alto because the WITH CHECK OPTION is specified.
CREATE VIEW palo_alto AS
SELECT * FROM customer
WHERE city = 'Palo Alto'
WITH CHECK OPTION
What do the WITH CHECK OPTION keywords really check and prevent? It is
possible to insert into a view a row that does not satisfy the conditions of the
view (that is, a row that is not visible through the view). It is also possible to
update a row of a view so that it no longer satisfies the conditions of the view.
For example, if the view was created without the WITH CHECK OPTION
keywords, you could insert a row through the view where the city is Los
Altos, or you could update a row through the view by changing the city from
Palo Alto to Los Altos.
To prevent such inserts and updates, you can add the WITH CHECK OPTION
keywords when you create the view. These keywords ask the database server
to test every inserted or updated row to ensure that it meets the conditions
that are set by the WHERE clause of the view. The database server rejects the
operation with an error if the row does not meet the conditions.
However, even if the view was created with the WITH CHECK OPTION
keywords, you can perform inserts and updates through the view to change
columns that are not part of the view definition. A column is not part of the
view definition if it does not appear in the WHERE clause of the SELECT
statement that defines the view.
SQL Statements 1-227
CREATE VIEW
Updating Through Views
If a view is built on a single table, the view is updatable if the SELECT statement
that defined it did not contain any of the following items:
■
Columns in the select list that are aggregate values
■
Columns in the select list that use the UNIQUE or DISTINCT keyword
■
A GROUP BY clause
■
A derived value for a column, which was created using an
arithmetical expression
In an updatable view, you can update the values in the underlying table by
inserting values into the view.
Important: You cannot update or insert rows in a remote table through views with
check options.
References
See the CREATE TABLE, DROP VIEW, GRANT, SELECT, and SET SESSION
AUTHORIZATION statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of views and
security in Chapter 10.
1-228
Informix Guide to SQL: Syntax
DATABASE
DATABASE
Use the DATABASE statement to select an accessible database as the current
database.
Syntax
+
DATABASE
Database
Name
p. 1-660
EXCLUSIVE
Usage
You can use the DATABASE statement to select any database on your database
server. To select a database on another OnLine database server, specify the
name of the database server with the database name.
If you specify the name of the current database server or another database
server with the database name, the database server name cannot be
uppercase.
Issuing a DATABASE statement when a database is already open closes the
current database before opening the new one. Closing the current database
releases any cursor resources held by the database server, which invalidates
any cursors you have declared up to that point. If the user identity was
changed through a SET SESSION AUTHORIZATION statement, the original
user name is restored.
The current user (or PUBLIC) must have the Connect privilege on the
database specified in the DATABASE statement. The current user cannot have
the same user name as an existing role in the database.
ESQL
You cannot include the DATABASE statement in a multistatement PREPARE
operation.
You can determine the type of database a user selects by checking the
warning flag after a DATABASE statement in the sqlca structure.
SQL Statements 1-229
DATABASE
If the database has transactions, the second element of the sqlwarn structure
contains a W after the DATABASE statement executes. See the following table
for the name of the variable that each SQL API product uses.
Product
Field Name
ESQL/C
sqlca.sqlwarn.sqlwarn1
ESQL/COBOL
SQLWARN1 OF SQLWARN OF SQLCA
♦
ESQL
ANSI
If the database is ANSI compliant, the third element of the sqlwarn structure
contains a W after the DATABASE statement executes. See the following table
for the name of the variable that each product uses.
Product
Field Name
ESQL/C
sqlca.sqlwarn.sqlwarn2
ESQL/COBOL
SQLWARN2 OF SQLWARN OF SQLCA
♦
ESQL
1-230
If the database is an INFORMIX-OnLine Dynamic Server database, the fourth
element of the sqlwarn structure contains a W after the DATABASE statement
executes. See the following table for the name of the variable that each
product uses.
Product
Field Name
ESQL/C
sqlca.sqlwarn.sqlwarn3
ESQL/COBOL
SQLWARN3 OF SQLWARN OF SQLCA
Informix Guide to SQL: Syntax
DATABASE
If the database is running in secondary mode, the seventh element of the
sqlwarn structure contains a W after the DATABASE statement executes. See
the following table for the name of the variable that each product uses.
Product
Field Name
ESQL/C
sqlca.sqlwarn.sqlwarn6
ESQL/COBOL
SQLWARN6 OF SQLWARN OF SQLCA
♦
SE
SE
ESQL
Only the databases stored in your current directory, or in a directory
specified in your DBPATH environment variable, are recognized. ♦
To specify a database that does not reside in your current directory or in a
directory specified by the DBPATH environment variable, follow the
DATABASE keyword with a program or host variable that evaluates to the full
pathname of the database (excluding the .dbs extension). ♦
EXCLUSIVE Keyword
The EXCLUSIVE keyword opens the database in exclusive mode and prevents
access by anyone but the current user. To allow others access to the database,
you must execute the CLOSE DATABASE statement and then reopen the
database without the EXCLUSIVE keyword.
The following statement opens the stores7 database on the training database
server in exclusive mode:
DATABASE stores7@training EXCLUSIVE
If another user has already opened the database, exclusive access is denied,
an error is returned, and no database is opened.
References
See the CLOSE DATABASE and CONNECT statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of database design
in Chapter 8 and implementing the data model in Chapter 9.
SQL Statements 1-231
DEALLOCATE DESCRIPTOR
DEALLOCATE DESCRIPTOR
Use the DEALLOCATE DESCRIPTOR statement to free a system-descriptor
area that was previously allocated for a specified descriptor or descriptor
variable.
Syntax
+
ESQL
DEALLOCATE DESCRIPTOR
'descriptor '
descriptor
variable
Element
descriptor
Purpose
Quoted string that identifies a
system-descriptor area
descriptor
variable
Host variable name that
identifies a system-descriptor
area
Restrictions
System-descriptor area must
already be allocated. The
surrounding quotes must be
single.
System-descriptor area must
already be allocated.
Syntax
Quoted String,
p. 1-757
Variable name must
conform to
language-specific
rules for variable
names.
Usage
The DEALLOCATE DESCRIPTOR statement frees all the memory that is
associated with the system-descriptor area that descriptor or descriptor variable
identifies. It also frees all the value descriptors (including memory for data
values in the value descriptors).
You can reuse a descriptor or descriptor variable after it is deallocated.
Deallocation occurs automatically at the end of the program.
If you deallocate a nonexistent descriptor or descriptor variable, an error
results.
1-232
Informix Guide to SQL: Syntax
DEALLOCATE DESCRIPTOR
E/C
You cannot use the DEALLOCATE DESCRIPTOR statement to deallocate an
sqlda structure. You can use it only to free the memory that is allocated for a
system-descriptor area. ♦
The following examples show the DEALLOCATE DESCRIPTOR statement for
INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL, respectively. In each
example, the first line shows an embedded-variable name, and the second
line shows a quoted string that identifies the allocated system-descriptor
area.
INFORMIX-ESQL/C
EXEC SQL deallocate descriptor :descname;
EXEC SQL deallocate descriptor 'desc1';
INFORMIX-ESQL/COBOL
EXEC SQL DEALLOCATE DESCRIPTOR :DESCNAME END-EXEC.
EXEC SQL DEALLOCATE DESCRIPTOR 'DESC1' END-EXEC.
References
See the ALLOCATE DESCRIPTOR, DECLARE, DESCRIBE, EXECUTE, FETCH, GET
DESCRIPTOR, OPEN, PREPARE, PUT, and SET DESCRIPTOR statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of dynamic SQL in
Chapter 5.
SQL Statements 1-233
DECLARE
DECLARE
Use the DECLARE statement to define a cursor that represents the active set
of rows that a SELECT, INSERT, or EXECUTE PROCEDURE statement specifies.
Syntax
ESQL
cursor
id
DECLARE
INSERT
Statement
(Subset)
p. 1-250
+
FOR
CURSOR
+
+
cursor
variable
WITH
HOLD
+
+
SELECT
Statement
(Subset)
p. 1-245
FOR READ ONLY
FOR
UPDATE
,
column
name
OF
SCROLL
CURSOR
FOR
WITH
HOLD
SELECT
Statement
p. 1-459
+
statement id
statement id
variable
EXECUTE
PROCEDURE
Statement
p. 1-293
1-234
Informix Guide to SQL: Syntax
DECLARE
Element
column name
Purpose
A column that you can update
through the cursor
cursor id
The name that the DECLARE
statement assigns to the cursor
and that refers to the cursor in
other statements
An embedded variable name
that holds the value of cursor id
cursor variable
statement id
statement id
variable
A statement identifier that is a
data structure representing the
text of a prepared statement
Restrictions
The specified column must exist,
but it does not have to be in the
select list of the SELECT clause.
You cannot specify a cursor
name that a previous DECLARE
statement in the same program
has specified.
Variable must be a character data
type.
Syntax
Identifier, p. 1-723
Identifier, p. 1-723
The name must
conform to
language-specific
rules for variable
names.
Identifier, p. 1-723,
and PREPARE,
p. 1-402
The statement id must have
already been specified in a
PREPARE statement in the same
program.
An embedded variable name
Variable must be a character data The name must
that holds the value of statement type.
conform to
id
language-specific
rules for variable
names.
Usage
The DECLARE statement associates the cursor with a SELECT, INSERT, or
EXECUTE PROCEDURE statement or with the statement identifier (statement id
or statement id variable) of a prepared statement.
The DECLARE statement assigns an identifier to the cursor, specifies its uses,
and directs the preprocessor to allocate storage to hold the cursor.
The DECLARE statement must precede any other statement that refers to the
cursor during the execution of the program.
SQL Statements 1-235
DECLARE
When the cursor is used with a SELECT statement, it is a data structure that
represents a specific location within the active set of rows that the SELECT
statement retrieved. You associate a cursor with an INSERT statement if you
want to add multiple rows to the database in an INSERT operation. When the
cursor is used with an INSERT statement, it represents the rows that the
INSERT statement is to add to the database. When the cursor is used with an
EXECUTE PROCEDURE statement, it represents the columns or values that the
stored procedure retrieved.
The amount of available memory in the system limits the number of open
cursors and prepared statements that you can have at one time in one
process. Use FREE statement id or FREE statement id variable to release the
resources that a prepared statement holds; use FREE cursor id or FREE cursor
variable to release resources that a cursor holds.
A program can consist of one or more source-code files. By default, the scope
of a cursor is global to a program, so a cursor declared in one file can be referenced from another file.
In a multiple-file program, if you want to limit the scope of cursors to the files
in which they are declared, you must preprocess all the files with the -local
command-line option. See your SQL API product manual for more information, restrictions, and performance issues when you preprocess with the
-local option.
E/C
E/CO
A variable used in place of the cursor name or statement identifier must be
the CHARACTER data type. In ESQL/C programs, the variable must be
defined as exec sql char. ♦
A variable that is used in place of the cursor name or statement identifier
must be the CHARACTER data type. In ESQL/COBOL programs, declare such
a variable as a standard CHARACTER type. ♦
To declare multiple cursors, use a single statement identifier. For instance, the
following INFORMIX-ESQL/C example does not return an error:
EXEC
EXEC
EXEC
EXEC
1-236
SQL
SQL
SQL
SQL
Informix Guide to SQL: Syntax
prepare
declare
declare
declare
id1 from
x cursor
y scroll
z cursor
'select * from customer';
for id1;
cursor for id1;
with hold for id1;
DECLARE
If you include the -ansi compilation flag (or if DBANSIWARN is set),
warnings are generated for statements that use dynamic cursor names or
dynamic statement identifier names. Some error checking is performed at
runtime. The following list indicates the typical checks:
■
Illegal use of cursors (that is, normal cursors used as scroll cursors)
■
Use of undeclared cursors
■
Bad cursor or statement names (empty)
Checks for multiple declarations of a cursor of the same name are performed
at compile time only if the cursor or statement is an identifier. For example,
the code in the first example below results in a compile error. The code in the
second example does not result in a compile error because it uses a host
variable to hold the cursor name.
Results in error
EXEC SQL declare x cursor for
select * from customer;
. . .
EXEC SQL declare x cursor for
select * from orders;
Runs successfully
EXEC SQL declare x cursor for
select * from customer;
. . .
stcopy("x", s);
EXEC SQL declare :s cursor for
select * from customer;
Overview of Cursor Types
Functionally, a cursor can be associated with a SELECT statement (a select
cursor), an EXECUTE PROCEDURE statement (a procedure cursor) that returns
values, or an INSERT statement (an insert cursor). You can use a select cursor
to update or delete rows; it is called an update cursor.
SQL Statements 1-237
DECLARE
A cursor can also be associated with a statement identifier, enabling you to
use a cursor with INSERT, SELECT, or EXECUTE PROCEDURE statements that
are prepared dynamically and to use different statements with the same
cursor at different times. In this case, the type of cursor depends on the
statement that is prepared at the time the cursor is opened (see the OPEN
statement on page 1-390).
Tip: Cursors for stored procedures behave the same as select cursors, which are
enabled as update cursors.
Select or Procedure Cursor
A select or procedure cursor enables you to scan multiple rows of data and to
move data row by row into a set of receiving variables, as the following steps
describe:
1.
Use a DECLARE statement to define a cursor for the SELECT
statement or for the EXECUTE PROCEDURE statement.
2.
Open the cursor with the OPEN statement. The database server
processes the query until it locates or constructs the first row of the
active set.
3.
Retrieve successive rows of data with the FETCH statement.
4.
Close the cursor with the CLOSE statement when the active set is no
longer needed.
5.
Free the cursor with the FREE statement. The FREE statement releases
the resources that are allocated for a declared cursor.
A select cursor can be explicitly declared as read only with the FOR READ
ONLY option.
Read-Only Cursor
Use the FOR READ ONLY option to state explicitly that a select cursor cannot
be used to modify data. In a database that is not ANSI compliant, a select
cursor and a select cursor that is built with the FOR READ ONLY option are the
same. Neither can be used to update data.
ANSI
1-238
In an ANSI-compliant database, if you want a select cursor to be read only,
you must use the FOR READ ONLY keywords when you declare the cursor. ♦
Informix Guide to SQL: Syntax
DECLARE
Update Cursor
Use the FOR UPDATE keywords to declare an update cursor. You can use the
update cursor to modify (update or delete) the current row.
ANSI
In an ANSI-compliant database, you can use a select cursor to update or
delete data as long as the cursor was not declared with the FOR READ ONLY
keywords and it follows the restrictions on update cursors that are described
in “Subset of the SELECT Statement Associated with Cursors” on page 1-245.
You do not need to use the FOR UPDATE keywords when you declare the
cursor. ♦
Insert Cursor
An insert cursor increases processing efficiency (compared with embedding
the INSERT statement directly). The insert cursor allows bulk insert data to be
buffered in memory and written to disk when the buffer is full. This process
reduces communication between the program and the database server and
also increases the speed of the insertions.
Cursor Characteristics
Structurally, you can declare a cursor as a sequential cursor (the default
condition), a scroll cursor (using the SCROLL keyword), or a hold cursor (using
the WITH HOLD keywords). The following sections explain these structural
characteristics.
Sequential Cursor
If you use only the CURSOR keyword in a DECLARE statement, you create a
sequential cursor, which can fetch only the next row in sequence from the
active set. The sequential cursor can read through the active set only once
each time it is opened. If you are using a sequential cursor, on each execution
of the FETCH statement, the database server returns the contents of the
current row and locates the next row in the active set.
The following INFORMIX-ESQL/C example is read only in a database that is
not ANSI compliant and read/updatable in an ANSI-compliant database:
EXEC SQL declare s_cur cursor for
select fname, lname into :st_fname, :st_lname
from orders where customer_num = 114;
SQL Statements 1-239
DECLARE
Scroll Cursor
The SCROLL keyword creates a scroll cursor, which you can use to fetch rows
of the active set in any sequence. To implement a scroll cursor, the database
server creates a temporary table to hold the active set. With the active set
retained as a table, you can fetch the first, last, or any intermediate rows as
well as fetch rows repeatedly without having to close and reopen the cursor.
See the FETCH statement on page 1-296 for a discussion of these abilities.
The database server retains the active set for a scroll cursor in a temporary
table until the cursor is closed. On a multiuser system, the rows in the tables
from which the active-set rows were derived might change after a copy is
made in the temporary table. (For information about temporary tables, see
the INFORMIX-OnLine Dynamic Server Administrator’s Guide.) If you use a
scroll cursor within a transaction, you can prevent copied rows from
changing either by setting the isolation level to Repeatable Read (available
only with INFORMIX-OnLine Dynamic Server) or by locking the entire table
in share mode during the transaction. (See the SET ISOLATION statement on
page 1-575 and the LOCK TABLE statement on page 1-387.)
The following example creates a scroll cursor:
DECLARE sc_cur SCROLL CURSOR FOR
SELECT * FROM orders
Hold Cursor
If you use the WITH HOLD keywords, you create a hold cursor. A hold cursor
remains open after a transaction ends. You can use the WITH HOLD keywords
to declare both sequential and scroll cursors. The following example creates
a hold cursor:
DECLARE hld_cur CURSOR WITH HOLD FOR
SELECT customer_num, lname, city FROM customer
A hold cursor allows uninterrupted access to a set of rows across multiple
transactions. Ordinarily, all cursors close at the end of a transaction; a hold
cursor does not close.
1-240
Informix Guide to SQL: Syntax
DECLARE
You can use a hold cursor as the following ESQL/C code example shows. This
code fragment uses a hold cursor as a master cursor to scan one set of records
and a sequential cursor as a detail cursor to point to records that are located
in a different table. The records that the master cursor scans are the basis for
updating the records to which the detail cursor points. The COMMIT WORK
statement at the end of each iteration of the first WHILE loop leaves the hold
cursor c_master open but closes the sequential cursor c_detail and releases
all locks. This technique minimizes the resources that the database server
must devote to locks and unfinished transactions, and it gives other users
immediate access to updated rows.
EXEC SQL BEGIN DECLARE SECTION;
int p_custnum,
int save_status;
long p_orddate;
EXEC SQL END DECLARE SECTION;
EXEC SQL prepare st_1 from
'select order_date
from orders where customer_num = ? for update';
EXEC SQL declare c_detail cursor for st_1;
EXEC SQL declare c_master cursor with hold for
select customer_num
from customer where city = 'Pittsburgh';
EXEC SQL open c_master;
if(SQLCODE==0) /* the open worked */
EXEC SQL fetch c_master into :p_custnum; /* discover first customer */
while(SQLCODE==0) /* while no errors and not end of pittsburgh customers */
{
EXEC SQL begin work; /* start transaction for customer p_custnum */
EXEC SQL open c_detail using :p_custnum;
if(SQLCODE==0) /* detail open succeeded */
EXEC SQL fetch c_detail into :p_orddate; /* get first order */
while(SQLCODE==0) /* while no errors and not end of orders */
{
EXEC SQL update orders set order_date = '08/15/94'
where current of c_detail;
if(status==0) /* update was ok */
EXEC SQL fetch c_detail into :p_orddate; /* next order */
}
if(SQLCODE==SQLNOTFOUND) /* correctly updated all found orders */
EXEC SQL commit work; /* make updates permanent, set status */
else /* some failure in an update */
{
save_status = SQLCODE; /* save error for loop control */
EXEC SQL rollback work;
SQLCODE = save_status; /* force loop to end */
}
if(SQLCODE==0) /* all updates, and the commit, worked ok */
EXEC SQL fetch c_master into :p_custnum; /* next customer? */
}
EXEC SQL close c_master;
SQL Statements 1-241
DECLARE
Use either the CLOSE statement to close the hold cursor explicitly or the
CLOSE DATABASE or DISCONNECT statements to close it implicitly. The
CLOSE DATABASE statement closes all cursors.
Declaring a Cursor as an Update or Read-Only Cursor
When you associate a cursor with a SELECT statement, you can define it as an
update cursor or as a read-only cursor, as follows:
■
Use the FOR UPDATE keywords to define the cursor as an update
cursor.
■
Use the FOR READ ONLY keywords to define the cursor as a
read-only cursor.
You cannot specify both the FOR UPDATE option and the FOR READ ONLY
option in the same DECLARE statement because these options are mutually
exclusive.
Defining an Update Cursor
Use the FOR UPDATE keywords to notify the database server that updating is
possible and cause it to use more stringent locking than with a select cursor.
You can specify particular columns that can be updated.
After you create an update cursor, you can update or delete the currently
selected row by using an UPDATE or DELETE statement with the WHERE
CURRENT OF clause. The words CURRENT OF refer to the row that was most
recently fetched; they take the place of the usual test expressions in the
WHERE clause.
An update cursor lets you perform updates that are not possible with the
UPDATE statement because the decision to update and the values of the new
data items can be based on the original contents of the row. Your program can
evaluate or manipulate the selected data before it decides whether to update.
The UPDATE statement cannot interrogate the table that is being updated.
ANSI
1-242
All simple select cursors are potentially update cursors even if they are
declared without the FOR UPDATE keywords. (See the restrictions on SELECT
statements associated with update cursors in “Subset of the SELECT
Statement Associated with Cursors” on page 1-245.) ♦
Informix Guide to SQL: Syntax
DECLARE
Locking with an Update Cursor
You declare an update cursor to let the database server know that the
program might update (or delete) any row that it fetches as part of the
SELECT statement. The update cursor employs promotable locks for rows that
the program fetches. Other programs can read the locked row, but no other
program can place a promotable or write lock. Before the program modifies
the row, the row lock is promoted to an exclusive lock.
SE
The INFORMIX-SE database server does not use promotable locks. Before the
program modifies a row, the database server obtains an exclusive lock on the
row. ♦
Although it is possible to declare an update cursor with the WITH HOLD
keywords, the only reason to do so is to break a long series of updates into
smaller transactions. You must fetch and update a particular row in the same
transaction.
If an operation involves fetching and updating a very large number of rows,
the lock table that the database server maintains can overflow. The usual way
to prevent this overflow is to lock the entire table that is being updated. If this
action is impossible, an alternative is to update through a hold cursor and to
execute COMMIT WORK at frequent intervals. However, you must plan such
an application very carefully because COMMIT WORK releases all locks, even
those that are placed through a hold cursor.
Using FOR UPDATE with a List of Columns
When you declare an update cursor, you can limit the update to specific
columns by including the OF keyword and a list of columns. You can modify
only those named columns in subsequent UPDATE statements. The columns
need not be in the select list of the SELECT clause.
This column restriction applies only to UPDATE statements. The OF column
clause has no effect on subsequent DELETE statements that use a WHERE
CURRENT OF clause. (A DELETE statement removes the contents of all
columns.)
SQL Statements 1-243
DECLARE
The principal advantage to specifying columns is documentation and
preventing programming errors. (The database server refuses to update any
other columns.) An additional advantage is speed, when the SELECT
statement meets the following criteria:
■
The SELECT statement can be processed using an index.
■
The columns that are listed are not part of the index that is used to
process the SELECT statement.
If the columns that you intend to update are part of the index that is used to
process the SELECT statement, the database server must keep a list of each
row that is updated to ensure that no row is updated twice. When you use
the OF keyword to specify the columns that can be updated, the database
server determines whether to keep the list of updated rows. If the database
server determines that the list is unnecessary, then eliminating the work of
keeping the list results in a performance benefit. If you do not use the OF
keyword, the database server keeps the list of updated rows, although it
might be unnecessary.
The following example contains INFORMIX-ESQL/C code that uses an update
cursor with a DELETE statement to delete the current row. Whenever the row
is deleted, the cursor remains between rows. After you delete data, you must
use a FETCH statement to advance the cursor to the next row before you can
refer to the cursor in a DELETE or UPDATE statement.
EXEC SQL declare q_curs cursor for
select * from customer where lname matches :last_name
for update;
EXEC SQL open q_curs;
for (;;)
{
EXEC SQL fetch q_curs into :cust_rec;
if (strncmp(SQLSTATE, "00", 2) != 0)
break;
/* Display customer values and prompt for answer */
printf("\n%s %s", cust_rec.fname, cust_rec.lname);
printf("\nDelete this customer? ");
scanf("%s", answer);
if (answer[0] == 'y')
EXEC SQL delete from customer where current of q_curs;
if (strncmp(SQLSTATE, "00", 2) != 0)
break;
}
printf("\n");
EXEC SQL close q_curs;
1-244
Informix Guide to SQL: Syntax
DECLARE
Defining a Read-Only Cursor
Use the FOR READ ONLY keywords to define a cursor as a read-only cursor.
The need for the FOR READ ONLY keywords depends on whether your
database is an ANSI-mode database or a database that is not ANSI compliant.
In a database that is not ANSI compliant, the cursor that the DECLARE
statement defines is a read-only cursor by default. So you do not need to
specify the FOR READ ONLY keywords if you want the cursor to be a readonly cursor. The only advantage of specifying the FOR READ ONLY keywords
explicitly is for better program documentation.
ANSI
In an ANSI-mode database, the cursor associated with a SELECT statement
through the DECLARE statement is an update cursor by default, provided
that the SELECT statement conforms to all of the restrictions for update
cursors listed in “Subset of the SELECT Statement Associated with Cursors”
below.
Therefore, you should use the FOR READ ONLY keywords in the DECLARE
statement only if you want the cursor to be a read-only cursor rather than an
update cursor. You declare a read-only cursor to let the database server know
that the program will not update (or delete) any row that it fetches as part of
the SELECT statement. The database server can use less stringent locking for
a read-only cursor than for an update cursor. ♦
Subset of the SELECT Statement Associated with Cursors
Not all SELECT statements can be associated with an update cursor or a
read-only cursor. If the DECLARE statement includes the FOR UPDATE clause
or the FOR READ ONLY clause, you must observe certain restrictions on the
SELECT statement that is included in the DECLARE statement (either directly
or as a prepared statement).
If the DECLARE statement includes the FOR UPDATE clause, the SELECT
statement must conform to the following restrictions:
■
The statement can select data from only one table.
■
The statement cannot include any aggregate functions.
■
The statement cannot include any of the following clauses or
keywords: DISTINCT, FOR READ ONLY, FOR UPDATE, GROUP BY,
INTO TEMP, ORDER BY, UNION, or UNIQUE.
SQL Statements 1-245
DECLARE
If the DECLARE statement includes the FOR READ ONLY clause, the SELECT
statement must conform to the following restrictions:
■
The SELECT statement cannot have a FOR READ ONLY clause.
■
The SELECT statement cannot have a FOR UPDATE clause.
For a complete description of SELECT syntax and usage, see the SELECT
statement on page 1-459.
Examples of Cursors in ANSI and non-ANSI Databases
In a database that is not ANSI compliant, a cursor associated with a SELECT
statement is a read-only cursor by default. The following example declares a
read-only cursor in a non-ANSI database:
EXEC SQL declare cust_curs cursor for
select * from customer_notansi;
If you want to make it clear in the program code that this cursor is a read-only
cursor, you can specify the FOR READ ONLY option as shown in the following
example:
EXEC SQL declare cust_curs cursor for
select * from customer_notansi
for read only;
If you want this cursor to be an update cursor, you need to specify the FOR
UPDATE option in your DECLARE statement. The following example declares
an update cursor:
EXEC SQL declare new_curs cursor for
select * from customer_notansi
for update;
If you want an update cursor to be able to modify only some of the columns
in a table, you need to specify these columns in the FOR UPDATE option.The
following example declares an update cursor and specifies that this cursor
can update only the fname and lname columns in the customer_notansi
table:
EXEC SQL declare name_curs cursor for
select * from customer_notansi
for update of fname, lname;
1-246
Informix Guide to SQL: Syntax
DECLARE
ANSI
In an ANSI-mode database, a cursor associated with a SELECT statement is an
update cursor by default. The following example declares an update cursor
in an ANSI-mode database:
EXEC SQL declare x_curs cursor for
select * from customer_ansi;
If you want to make it clear in the program documentation that this cursor is
an update cursor, you can specify the FOR UPDATE option as shown in the
following example:
EXEC SQL declare x_curs cursor for
select * from customer_ansi
for update;
If you want an update cursor to be able to modify only some of the columns
in a table, you must specify these columns in the FOR UPDATE option. The
following example declares an update cursor and specifies that this cursor
can update only the fname and lname columns in the customer_ansi table:
EXEC SQL declare y_curs cursor for
select * from customer_ansi
for update of fname, lname;
If you want a cursor to be a read-only cursor, you must override the default
behavior of the DECLARE statement by specifying the FOR READ ONLY
option in your DECLARE statement. The following example declares a
read-only cursor:
EXEC SQL declare z_curs cursor for
select * from customer_ansi
for read only;
♦
Associating a Cursor with a Prepared Statement
The PREPARE statement lets you assemble the text of an SQL statement at
runtime and pass the statement text to the database server for execution. If
you anticipate that a dynamically prepared SELECT statement or EXECUTE
PROCEDURE statement that returns values could produce more than one row
of data, the prepared statement must be associated with a cursor. (See the
PREPARE statement on page 1-402 for more information about preparing SQL
statements.)
SQL Statements 1-247
DECLARE
The result of a PREPARE statement is a statement identifier (statement id or id
variable), which is a data structure that represents the prepared statement
text. You declare a cursor for the statement text by associating a cursor with
the statement identifier.
You can associate a sequential cursor with any prepared SELECT or EXECUTE
PROCEDURE statement. You cannot associate a scroll cursor with a prepared
INSERT statement or with a SELECT statement that was prepared to include a
FOR UPDATE clause.
After a cursor is opened, used, and closed, a different statement can be
prepared under the same statement identifier. In this way, it is possible to use
a single cursor with different statements at different times. The cursor must
be redeclared before you use it again.
The following example contains INFORMIX-ESQL/C code that prepares a
SELECT statement and declares a cursor for the prepared statement text. The
statement identifier st_1 is first prepared from a SELECT statement that
returns values; then the cursor c_detail is declared for st_1.
EXEC SQL prepare st_1 from
'select order_date
from orders where customer_num = ?';
EXEC SQL declare c_detail cursor for st_1;
If you want use a prepared SELECT statement to modify data, add a FOR
UPDATE clause to the statement text that you wish to prepare, as the
following INFORMIX-ESQL/C example shows:
EXEC SQL prepare sel_1 from 'select * from customer for update';
EXEC SQL declare sel_curs cursor for sel_1;
Using Cursors with Transactions
To roll back a modification, you must perform the modification within a
transaction. A transaction in a database that is not ANSI-compliant begins
only when the BEGIN WORK statement is executed.
ANSI
1-248
In ANSI-compliant databases, transactions are always in effect. ♦
Informix Guide to SQL: Syntax
DECLARE
The database server enforces the following guidelines for select and update
cursors. These guidelines ensure that modifications can be committed or
rolled back properly:
■
Open an insert or update cursor within a transaction.
■
Include PUT and FLUSH statements within one transaction.
■
Modify data (update, insert, or delete) within one transaction.
The database server lets you open and close a hold cursor for an update
outside a transaction; however, you should fetch all the rows that pertain to
a given modification and then perform the modification all within a single
transaction. You cannot open and close hold or update cursors outside a
transaction.
The following example produces an error when the database server tries to
execute the UPDATE statement:
Results in error
EXEC SQL declare q_curs cursor for
select customer_num, fname, lname from customer
where lname matches :last_name
for update;
EXEC SQL open q_curs;
EXEC SQL fetch q_curs into :cust_rec; /* fetch before begin */
EXEC SQL begin work;
EXEC SQL update customer set lname = 'Smith'
where current of q_curs;
/* error here */
EXEC SQL commit work;
The following example does not produce an error when the database server
tries to execute the UPDATE statement:
Runs successfully
EXEC SQL declare q_curs cursor for
select customer_num, fname, lname from customer
where lname matches :last_name
for update;
EXEC SQL open q_curs;
EXEC SQL begin work;
EXEC SQL fetch q_curs into :cust_rec; /* fetch after begin */
EXEC SQL update customer set lname = 'Smith'
where current of q_curs;
/* no error */
EXEC SQL commit work;
SQL Statements 1-249
DECLARE
When you update a row within a transaction, the row remains locked until
the cursor is closed or the transaction is committed or rolled back. If you
update a row when no transaction is in effect, the row lock is released when
the modified row is written to disk.
If you update or delete a row outside a transaction, you cannot roll back the
operation.
A cursor that is declared for insert is an insert cursor. In a database that uses
transactions, you cannot open an insert cursor outside a transaction unless it
was also declared with hold.
Subset of INSERT Associated with a Sequential Cursor
To create an insert cursor, you associate a sequential cursor with a restricted
form of the INSERT statement. The INSERT statement must include a VALUES
clause; it cannot contain an embedded SELECT statement.
The following example contains INFORMIX-ESQL/C code that declares an
insert cursor:
EXEC SQL declare ins_cur cursor for
insert into stock values
(:stock_no,:manu_code,:descr,:u_price,:unit,:u_desc);
The insert cursor simply inserts rows of data; it cannot be used to fetch data.
When an insert cursor is opened, a buffer is created in memory to hold a
block of rows. The buffer receives rows of data as the program executes PUT
statements. The rows are written to disk only when the buffer is full. You can
use the CLOSE, FLUSH, or COMMIT WORK statement to flush the buffer when
it is less than full. This topic is discussed further under the PUT and CLOSE
statements. You must close an insert cursor to insert any buffered rows into
the database before the program ends. You can lose data if you do not close
the cursor properly.
1-250
Informix Guide to SQL: Syntax
DECLARE
Using an Insert Cursor with Hold
If you associate a hold cursor with an INSERT statement, you can use transactions to break a long series of PUT statements into smaller sets of PUT
statements. Instead of waiting for the PUT statements to fill the buffer and
trigger an automatic write to the database, you can execute a COMMIT WORK
statement to flush the row buffer. If you use a hold cursor, the COMMIT WORK
statement commits the inserted rows but leaves the cursor open for further
inserts. This method can be desirable when you are inserting a large number
of rows, because pending uncommitted work consumes database server
resources.
References
See the CLOSE, DELETE, EXECUTE PROCEDURE, FETCH, FREE, INSERT, OPEN,
PREPARE, PUT, SELECT, and UPDATE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of cursors and data
modification in Chapter 5 and Chapter 6, respectively.
SQL Statements 1-251
DELETE
DELETE
Use the DELETE statement to delete one or more rows from a table.
Syntax
DELETE FROM
Table
Name
p. 1-768
View
Name
p. 1-772
Synonym
Name
p. 1-766
Element
cursor name
Purpose
The name of the cursor whose
current row is to be deleted
WHERE
Condition
p. 1-643
ESQL
CURRENT
OF
Restrictions
The cursor must have been
previously declared in a
DECLARE statement with a FOR
UPDATE clause.
cursor
name
Syntax
Identifier, p. 1-723
Usage
If you use the DELETE statement without a WHERE clause, all the rows in the
table are deleted.
If you use the DELETE statement outside a transaction in a database that uses
transactions, each DELETE statement that you execute is treated as a single
transaction.
Each row affected by a DELETE statement within a transaction is locked for
the duration of the transaction; therefore, a single DELETE statement that
affects a large number of rows locks the rows until the entire operation is
complete. If the number of rows affected is very large, you might exceed the
limits your operating system places on the maximum number of simultaneous locks. If this occurs, you can either reduce the scope of the DELETE
statement or lock the entire table before you execute the statement.
1-252
Informix Guide to SQL: Syntax
DELETE
If you specify a view name, the view must be updatable. See “Updating
Through Views” on page 1-228 for an explanation of an updatable view.
DB
If you omit the WHERE clause while you are working within the SQL menu,
DB-Access prompts you to verify that you want to delete all rows from a table.
You do not receive a prompt if you run the DELETE statement within a
command file. ♦
ANSI
Statements are always within an implicit transaction in an ANSI-compliant
database; therefore, you cannot have a DELETE statement outside a
transaction. ♦
Using Cascading Deletes
Use the ON DELETE CASCADE option of the REFERENCES clause on either the
CREATE TABLE or ALTER TABLE statement to specify that you want deletes to
cascade from one table to another. For example, the stock table contains the
column stock_num as a primary key. The catalog and items tables each
contain the column stock_num as foreign keys with the ON DELETE
CASCADE option specified. When a delete is performed from the stock table,
rows are also deleted in the catalog and items tables, which are referred
through the foreign keys.
If a cascading delete is performed without a WHERE clause, all rows in the
parent table (and subsequently, the affected child tables) are deleted.
WHERE Clause
Use the WHERE clause to specify one or more rows that you want to delete.
The WHERE conditions are the same as the conditions in the SELECT
statement. For example, the following statement deletes all the rows of the
items table where the order number is less than 1034:
DELETE FROM items
WHERE order_num < 1034
DB
If you include a WHERE clause that selects all rows in the table, DB-Access
gives no prompt and deletes all rows. ♦
SQL Statements 1-253
DELETE
Deleting and the WHERE Clause
ANSI
If you delete from a table in an ANSI-compliant database using a WHERE
clause and no rows are found, you can detect this condition using the GET
DIAGNOSTICS statement. The RETURNED_SQLSTATE field of the GET
DIAGNOSTICS statement contains the value ‘02000.’ In a database that is not
ANSI compliant, no error is returned. ♦
If you delete from a table using a WHERE clause in a multistatement prepare
in either ANSI databases and databases that are not ANSI-compliant and no
rows are found, you receive a RETURNED_SQLSTATE field value of ‘02000.’
For additional information about the SQLSTATE code, see the GET
DIAGNOSTICS statement in this manual.
You can also use the SQLCODE field of sqlca to determine the same results.
See the Informix Guide to SQL: Tutorial for further information about the
SQLCODE field of sqlca.
CURRENT OF Clause
ESQL
To use the CURRENT OF clause, you must have previously used the DECLARE
statement with the FOR UPDATE clause to announce the cursor name.
If you use the CURRENT OF clause, the DELETE statement removes the row of
the active set at the current position of the cursor. After the deletion, no
current row exists; you cannot use the cursor to delete or update a row until
you reposition the cursor with a FETCH statement. ♦
ANSI
ESQL
All select cursors are potentially update cursors in ANSI-compliant
databases. You can use the CURRENT OF clause with any select cursor. ♦
References
See the INSERT, UPDATE, DECLARE, GET DIAGNOSTICS, and FETCH
statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of cursors and data
modification in Chapter 5 and Chapter 6, respectively.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
DELETE statement.
1-254
Informix Guide to SQL: Syntax
DESCRIBE
DESCRIBE
Use the DESCRIBE statement to obtain information about a prepared
statement before you execute it. The DESCRIBE statement returns the
prepared statement type. For a SELECT, EXECUTE PROCEDURE, or INSERT
statement, the DESCRIBE statement also returns the number, data types and
size of the values, and the name of the column or expression that the query
returns. The information can be stored in a system-descriptor area or, in
ESQL/C, in an sqlda structure.
Syntax
ESQL
+
DESCRIBE
USING
SQL DESCRIPTOR
statement id
statement
id variable
E/C
descriptor
variable
INTO
Element
descriptor
descriptor
variable
Purpose
Quoted string that identifies a
system-descriptor area
Host variable name that
identifies a system-descriptor
area
'descriptor '
sqlda pointer
Restrictions
System-descriptor area must
already be allocated.
Variable must contain the name
of an allocated systemdescriptor area.
Syntax
Quoted String,
p. 1-757
Variable name must
conform to
language-specific
rules for variable
names.
(1 of 2)
SQL Statements 1-255
DESCRIBE
Element
sqlda pointer
Purpose
A pointer to an sqlda structure
statement id
Statement identifier for a
prepared SQL statement
statement id
variable
Host variable that contains a
statement identifier for a
prepared SQL statement
Restrictions
You cannot begin an sqlda
pointer with a dollar sign ($) or a
colon (:). You must use an sqlda
structure if you are using
dynamic SQL statements.
The statement identifier must be
defined in a previous PREPARE
statement.
The statement identifier must be
defined in a previous PREPARE
statement. The variable must be
a character data type.
Syntax
See the discussion of
sqlda structure in the
INFORMIX-ESQL/
C Programmer’s
Manual.
PREPARE, p. 1-402
Variable name must
conform to
language-specific
rules for variable
names.
(2 of 2)
Usage
The DESCRIBE statement allows you to determine, at runtime, the type of
statement that has been prepared and the number and types of data that a
prepared query returns when it is executed. With this information, you can
write code to allocate memory to hold retrieved values and display or
process them after they are fetched.
Describing the Statement Type
The DESCRIBE statement takes a statement identifier from a PREPARE
statement as input. When the DESCRIBE statement executes, the database
server sets the value of the SQLCODE field of the sqlca (see the manual for
your SQL API product) to indicate the statement type (that is, the keyword
with which the statement begins). If the prepared statement text contains
more than one SQL statement, the DESCRIBE statement returns the type of the
first statement in the text.
SQLCODE is set to zero to indicate a SELECT statement without an INTO TEMP
clause. This situation is the most common. For any other SQL statement,
SQLCODE is set to a positive integer. See the manual for your SQL API product
for more information about possible SQLCODE values after a DESCRIBE
statement.
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Informix Guide to SQL: Syntax
DESCRIBE
You can test the number against the constant names that are defined. In
INFORMIX-ESQL/C, the constant names are defined in the sqlstype.h header
file. A printed list of the possible values and their constant names appears in
the manual for each SQL API product.
The DESCRIBE statement uses the SQLCODE field differently than any other
statement, possibly returning a nonzero value when it executes successfully.
You can revise standard error-checking routines to accommodate this
behavior, if desired.
Checking for Existence of a WHERE Clause
If the DESCRIBE statement detects that a prepared statement contains an
UPDATE or DELETE statement without a WHERE clause, the DESCRIBE
statement sets the following sqlca variable to W.
Product
Field Name
ESQL/C
sqlca.sqlwarn.sqlwarn4
ESQL/COBOL
SQLWARN4 OF SQLWARN OF SQLCA
Without a WHERE clause, the update or delete action is applied to the entire
table. Check this variable to avoid unintended global changes to your table.
Describing SELECT, EXECUTE PROCEDURE, or INSERT
If the prepared statement text includes a SELECT statement without an INTO
TEMP clause, an EXECUTE PROCEDURE statement, or an INSERT statement,
the DESCRIBE statement also returns a description of each column or
expression that is included in the SELECT, EXECUTE PROCEDURE, or INSERT
list. These descriptions are stored in a system-descriptor area or in a pointer
to an sqlda structure.
The description includes the following information:
■
The data type of the column, as defined in the table
■
The length of the column, in bytes
■
The name of the column or expression
SQL Statements 1-257
DESCRIBE
See Chapter 5 of the Informix Guide to SQL: Tutorial for more information on
the system-descriptor area.
You can modify the system-descriptor-area information and use it in
statements that support a USING SQL DESCRIPTOR clause, such as EXECUTE,
FETCH, OPEN, and PUT. You must modify the system-descriptor area to show
the address in memory that is to receive the described value. You can change
the data type to another compatible type. This change causes data conversion
to take place when the data is fetched.
In addition to Chapter 5 of the Informix Guide to SQL: Tutorial, see the manual
for your SQL API for further information about interpreting and using the
data that is contained in the system-descriptor area.
USING SQL DESCRIPTOR Clause
The USING SQL DESCRIPTOR clause lets you store the description of a SELECT,
INSERT, or EXECUTE PROCEDURE list in a system-descriptor area that an
ALLOCATE DESCRIPTOR statement creates. You can obtain information about
the resulting columns of a prepared statement through a system-descriptor
area. Use the USING SQL DESCRIPTOR keywords and a descriptor to point to
a system-descriptor area instead of to an sqlda structure.
The DESCRIBE statement sets the COUNT field in the system-descriptor area
to the number of values in the SELECT, EXECUTE PROCEDURE, or INSERT list.
If COUNT is greater than the number of item descriptors (occurrences) in the
system-descriptor area, the system returns an error. Otherwise, the TYPE,
LENGTH, NAME, SCALE, PRECISION, and NULLABLE information is set and
memory for DATA fields is allocated automatically.
After a DESCRIBE statement is executed, the SCALE and PRECISION fields
contain the scale and precision of the column, respectively. If SCALE and
PRECISION are set in the SET DESCRIPTOR statement, and TYPE is set to
DECIMAL or MONEY, the LENGTH field is modified to adjust for the scale and
precision of the decimal value. If TYPE is not set to DECIMAL or MONEY, the
values for SCALE and PRECISION are not set, and LENGTH is unaffected.
The following examples show the use of a system descriptor in a DESCRIBE
statement in INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL. In the first
example in each pair, the descriptor is a quoted string; in the second example
in each pair, it is an embedded variable name.
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DESCRIBE
INFORMIX-ESQL/C
main()
{
. . .
EXEC SQL allocate descriptor 'desc1' with max 3;
EXEC SQL prepare curs1 FROM 'select * from tab';
EXEC SQL describe curs1 using sql descriptor 'desc1';
}
EXEC SQL describe curs1 using sql descriptor :desc1var;
INFORMIX-ESQL/COBOL
EXEC SQL ALLOCATE DESCRIPTOR 'DESC1' WITH MAX 3 END-EXEC.
EXEC SQL PREPARE CURS1 FROM 'SELECT * FROM TAB' END-EXEC.
EXEC SQL DESCRIBE CURS1 USING SQL DESCRIPTOR 'DESC1' END-EXEC.
EXEC SQL DESCRIBE CURS1 USING SQL DESCRIPTOR :DESC1VAR END-EXEC.
INTO sqlda pointer Clause
E/C
The INTO sqlda pointer clause lets you allocate memory for an sqlda structure
and store its address in an sqlda pointer. The DESCRIBE statement fills in the
allocated memory with descriptive information. The DESCRIBE statement
sets the sqlda.sqld field to the number of values in the SELECT, INSERT, or
EXECUTE PROCEDURE list. The sqlda structure also contains an array of data
descriptors (sqlvar structures), one for each value in the SELECT, INSERT, or
EXECUTE PROCEDURE list. After a DESCRIBE statement is executed, the
sqlda.sqlvar structure has the sqltype, sqllen, and sqlname fields set.
The DESCRIBE statement allocates memory for an sqlda pointer once it is
declared in a program. However, the application program must designate the
storage area of the sqlda.sqlvar.sqldata fields.
See the INFORMIX-ESQL/C Programmer’s Manual for further information on
the sqlda structure. ♦
E/CO
This product does not support pointers to an sqlda structure; it returns an
error if you try to execute a DESCRIBE statement that uses one. Only systemdescriptor areas that are allocated with the ALLOCATE DESCRIPTOR
statement can be used in a DESCRIBE statement in INFORMIX-ESQL/COBOL.
You can view the contents of the columns by executing a GET DESCRIPTOR
statement following a DESCRIBE statement on the specified system
descriptor. ♦
SQL Statements 1-259
DESCRIBE
References
See the ALLOCATE DESCRIPTOR, DEALLOCATE DESCRIPTOR, DECLARE,
EXECUTE, FETCH, GET DESCRIPTOR, OPEN, PREPARE, PUT, and SET
DESCRIPTOR statements in this manual for further information about using
dynamic management statements.
In the Informix Guide to SQL: Tutorial, see the discussion of the DESCRIBE
statement in Chapter 5.
For further information about how to use a system-descriptor area or an
sqlda pointer if you intend to use a FETCH...USING DESCRIPTOR or an
INSERT...USING DESCRIPTOR statement, refer to the manual for your SQL API
product.
1-260
Informix Guide to SQL: Syntax
DISCONNECT
DISCONNECT
The DISCONNECT statement terminates a connection between an application
and a database server.
Syntax
Element
Purpose
Usage
The DISCONNECT statement lets you terminate a connection to a database
server. If a database is open, it closes before the connection drops. Even if you
made a connection to a specific database only, that connection to the database
server is terminated by the DISCONNECT statement.
You cannot use the PREPARE statement for the DISCONNECT statement.
SQL Statements 1-261
DISCONNECT
ESQL
If you disconnect a specific connection using connection name or conn_nm
variable, DISCONNECT generates an error if the specified connection is not a
current or dormant connection.
A DISCONNECT statement that does not terminate the current connection
does not change the context of the current environment (the connection
context). ♦
The DEFAULT Option
Use the DEFAULT option to identify the default connection for a
DISCONNECT statement. The default connection is one of the following
connections:
■
An explicit default connection (a connection established with the
CONNECT TO DEFAULT statement)
■
An implicit default connection (any connection made using the
DATABASE, CREATE DATABASE, or START DATABASE statements)
You can use DISCONNECT to disconnect the default connection. See “The
DEFAULT Option” on page 1-91 and “The Implicit Connection with
DATABASE Statements” on page 1-92 for more information.
If the DATABASE statement does not specify a database server, as shown in
the following example, the default connection is made to the default database
server:
EXEC SQL database 'stores7';
.
.
.
EXEC SQL disconnect default;
If the DATABASE statement specifies a database server, as shown in the
following example, the default connection is made to that database server:
EXEC SQL database 'stores7@mydbsrvr';
.
.
.
EXEC SQL disconnect default;
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DISCONNECT
In either case, the DEFAULT option of DISCONNECT disconnects this default
connection. See “The DEFAULT Option” on page 1-91 and “The Implicit
Connection with DATABASE Statements” on page 1-92 for more information
about the default database server and implicit connections.
The CURRENT Keyword
Use the CURRENT keyword with the DISCONNECT statement as a shorthand
form of identifying the current connection. The CURRENT keyword replaces
the current connection name. For example, the DISCONNECT statement in the
following excerpt terminates the current connection to the database server
mydbsrvr:
CONNECT TO 'stores7@mydbsrvr'
.
.
.
DISCONNECT CURRENT
When a Transaction is Active
When a transaction is active, the DISCONNECT statement generates an error.
The transaction remains active, and the application must explicitly commit it
or roll it back. If an application terminates without issuing a DISCONNECT
statement (because of a system crash or program error, for example), active
transactions are rolled back.
Disconnecting in a Thread-Safe Environment
E/C
If you issue the DISCONNECT statement in a thread-safe ESQL/C application,
keep in mind that an active connection can only be disconnected from within
the thread in which it is active. Therefore one thread cannot disconnect
another thread’s active connection. The DISCONNECT statement generates an
error if such an attempt is made.
However, once a connection becomes dormant, any other thread can disconnect this connection unless an ongoing transaction is associated with the dormant connection (the connection was established with the WITH
CONCURRENT TRANSACTION clause of CONNECT). If the dormant connection was not established with the WITH CONCURRENT TRANSACTION
clause, DISCONNECT generates an error when it tries to disconnect it.
SQL Statements 1-263
DISCONNECT
See the SET CONNECTION statement on page 1-527 for an explanation of connections in a thread-safe ESQL/C application. ♦
Specifying the ALL Option
Use the keyword ALL to terminate all connections established by the application up to that time. For example, the following DISCONNECT statement
disconnects the current connection as well as all dormant connections:
DISCONNECT ALL
E/C
The ALL keyword has the same effect on multithreaded applications that it
has on single-threaded applications. Execution of the DISCONNECT ALL
statement causes all connections in all threads to be terminated. However, the
DISCONNECT ALL statement fails if any of the connections is in use or has an
ongoing transaction associated with it. If either of these conditions is true,
none of the connections is disconnected. ♦
References
See the CONNECT, SET CONNECTION, and DATABASE statements in this
manual.
For information on multithreaded applications, see the INFORMIX-ESQL/C
Programmer’s Manual.
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Informix Guide to SQL: Syntax
DROP AUDIT
DROP AUDIT
Use the DROP AUDIT statement to delete an audit-trail file.
Syntax
SE
+
DROP AUDIT FOR
Table Name
p. 1-768
Synonym
Name
p. 1-766
Usage
When you finish making a backup of your database files, use the DROP
AUDIT statement to remove the old audit-trail file. Use the CREATE AUDIT
statement to start a new audit trail for a table.
You must own the table or have the DBA privilege to use the DROP AUDIT
statement.
The following example assumes that you have just backed up the stores7
database. It removes the existing audit trail for the orders table.
DROP AUDIT FOR orders
References
See the CREATE AUDIT and RECOVER TABLE statements in this manual.
In the INFORMIX-SE Administrator’s Guide, see the discussion on audit trails.
SQL Statements 1-265
DROP DATABASE
You can specify the full pathname of the database in quotes, as the following
example shows:
DROP DATABASE '/u/training/stores7'
You cannot use a ROLLBACK WORK statement to undo a DROP DATABASE
statement. If you roll back a transaction that contains a DROP DATABASE
statement, the database is not re-created, and you do not receive an error
message. ♦
SE
ESQL
You can specify a database that is not in your local directory or DBPATH by
putting the full operating-system file in a variable for the database name, as
the following example shows:
LET db_var = '/u/training/stores7'
DROP DATABASE db_var
♦
DB
ESQL
Use this statement with caution. DB-Access does not prompt you to verify
that you want to delete the entire database. ♦
You can use a simple database name in a program or host variable, or you can
use the full database server and database name. See “Database Name” on
page 1-660 for more information. ♦
References
See the CREATE DATABASE and CLOSE DATABASE statements in this manual.
SQL Statements 1-267
DROP INDEX
DROP INDEX
Use the DROP INDEX statement to remove an index.
Syntax
+
DROP INDEX
Index
Name
p. 1-741
Usage
You must be the owner of the index or have the DBA privilege to use the
DROP INDEX statement.
The following example drops the index o_num_ix that joed owns. The
stores7 database must be the current database.
DROP INDEX stores7:joed.o_num_ix
You cannot use the DROP INDEX statement on a column or columns to drop
a unique constraint that is created with a CREATE TABLE statement; you must
use the ALTER TABLE statement to remove indexes that are created as
constraints with a CREATE TABLE or ALTER TABLE statement.
The index is not actually dropped if it is shared by constraints. Instead, it is
renamed in the sysindexes system catalog table with the following format:
[space]<tabid>_<constraint id>
In this example, tabid and constraint_id are from the systables and
sysconstraints system catalog tables, respectively. The idxname (index
name) column in the sysconstraints table is then updated to reflect this
change. For example, the renamed index name might be something like this:
“121_13” (quotes used to show the spaces).
If this index is a unique index with only referential constraints sharing it, the
index is downgraded to a duplicate index after it is renamed.
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Informix Guide to SQL: Syntax
DROP INDEX
SE
You cannot use a ROLLBACK WORK statement to undo a DROP INDEX
statement. If you roll back a transaction that contains a DROP INDEX
statement, the index is not re-created, and you do not receive an error
message. ♦
References
See the ALTER TABLE, CREATE INDEX, and CREATE TABLE statements in this
manual.
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of indexes.
SQL Statements 1-269
DROP PROCEDURE
DROP PROCEDURE
Use the DROP PROCEDURE statement to remove a stored procedure from the
database.
Syntax
+
DROP PROCEDURE
Procedure
Name
p. 1-754
Usage
You must be the owner of the stored procedure or have the DBA privilege to
use the DROP PROCEDURE statement.
Dropping the stored procedure removes the text and executable versions of
the procedure.
SE
You cannot use a ROLLBACK WORK statement to undo a DROP PROCEDURE
statement. If you roll back a transaction that contains a DROP PROCEDURE
statement, the stored procedure is not re-created, and you do not receive an
error message. ♦
Tip: You cannot drop a stored procedure from within the same procedure.
References
See the CREATE PROCEDURE statement in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of using stored
procedures in Chapter 12.
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Informix Guide to SQL: Syntax
DROP ROLE
DROP ROLE
Use the DROP ROLE statement to remove a previously created role.
Syntax
+
DROP ROLE
OL
role name
Element
Purpose
Restrictions
role name
Name of the role being dropped The role name must have been
created with the CREATE ROLE
statement
Syntax
Identifier, p. 1-723
Usage
The DROP ROLE statement is used to remove an existing role. Either the DBA
or a user to whom the role was granted with the WITH GRANT OPTION can
issue the DROP ROLE statement.
After a role is dropped, the privileges associated with that role, such as tablelevel privileges or fragment-level privileges, are dropped, and a user cannot
grant or enable a role. If a user is using the privileges of a role when the role
is dropped, the user automatically loses those privileges.
A role exists until either the DBA or a user to whom the role was granted with
the WITH GRANT OPTION uses the DROP ROLE statement to drop the role.
The following statement drops the role engineer:
DROP ROLE engineer
References
See the CREATE ROLE, GRANT, REVOKE, and SET ROLE statements in this
manual.
SQL Statements 1-271
DROP SYNONYM
DROP SYNONYM
Use the DROP SYNONYM statement to remove a previously defined
synonym.
Syntax
+
DROP SYNONYM
Synonym
Name
p. 1-766
Usage
You must be the owner of the synonym or have the DBA privilege to use the
DROP SYNONYM statement.
The following statement drops the synonym nj_cust, which cathyg owns:
DROP SYNONYM cathyg.nj_cust
If a table is dropped, any synonyms that are in the same database as the table
and that refer to the table are also dropped.
If a synonym refers to an external table, and the table is dropped, the
synonym remains in place until you explicitly drop it using DROP SYNONYM.
You can create another table or synonym in place of the dropped table and
give the new object the name of the dropped table. The old synonym then
refers to the new object. See the CREATE SYNONYM statement for a complete
discussion of synonym chaining.
SE
1-272
You cannot use a ROLLBACK WORK statement to undo a DROP SYNONYM
statement. If you roll back a transaction that contains a DROP SYNONYM
statement, the synonym is not re-created, and you do not receive an error
message. ♦
Informix Guide to SQL: Syntax
DROP SYNONYM
References
See the CREATE SYNONYM statement in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of synonyms in
Chapter 11.
SQL Statements 1-273
DROP TABLE
DROP TABLE
Use the DROP TABLE statement to remove a table, along with its associated
indexes and data.
Syntax
+
DROP TABLE
Table
Name
p. 1-768
Synonym
Name
p. 1-766
CASCADE
RESTRICT
Usage
You must be the owner of the table or have the DBA privilege to use the DROP
TABLE statement.
DB
SE
If you issue a DROP TABLE statement, you are not prompted to verify that you
want to delete an entire table. ♦
You cannot use a ROLLBACK WORK statement to undo a DROP TABLE
statement. If you roll back a transaction that contains a DROP TABLE
statement, the table is not re-created, and you do not receive an error
message. ♦
Effects of DROP TABLE Statement
Use the DROP TABLE statement with caution. When you remove a table, you
also delete the data stored in it, the indexes or constraints on the columns
(including all the referential constraints placed on its columns), any local
synonyms assigned to it, any triggers created for it, and any authorizations
you have granted on the table. You also drop all views based on the table and
any violations and diagnostics tables associated with the table. You do not
remove any synonyms for the table that have been created in an external
database.
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Informix Guide to SQL: Syntax
DROP TABLE
Examples of Dropping a Table
The following example deletes two tables. Both tables are within the current
database and are owned by the current user. Neither table has a violations or
diagnostics table associated with it. Neither table has a referential constraint
or view defined on it.
DROP TABLE customer;
DROP TABLE stores7@accntg:joed.state;
References
See the CREATE TABLE and DROP DATABASE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of data integrity and
creating a table in Chapter 4 and Chapter 9, respectively.
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Informix Guide to SQL: Syntax
DROP TRIGGER
DROP TRIGGER
Use the DROP TRIGGER statement to remove a trigger definition from the
database.
Syntax
DB
ESQL
+
DROP TRIGGER
Trigger
Name
p. 1-196
Usage
You must be the owner of the trigger or have the DBA privilege to drop a
trigger.
Dropping a trigger removes the text of the trigger definition and the
executable trigger from the database.
The following statement drops the items_pct trigger:
DROP TRIGGER items_pct
You cannot drop a trigger inside a stored procedure if the procedure is called
within a data manipulation statement. For example, in the following INSERT
statement, a DROP TRIGGER statement is illegal inside the stored procedure
proc1:
INSERT INTO orders EXECUTE PROCEDURE proc1(vala, valb)
SE
You cannot use a ROLLBACK WORK statement to undo a DROP TRIGGER
statement. If you roll back a transaction that contains a DROP TRIGGER
statement, the trigger is not re-created, and you do not receive an error
message. ♦
SQL Statements 1-277
DROP TRIGGER
References
See the CREATE PROCEDURE statement in this manual for more information
about a stored procedure that is called within a data manipulation statement.
For more information about triggers, see the CREATE TRIGGER statement in
this manual.
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Informix Guide to SQL: Syntax
DROP VIEW
DROP VIEW
Use the DROP VIEW statement to remove a view from the database.
Syntax
+
DROP VIEW
View
Name
p. 1-772
CASCADE
Synonym
Name
p. 1-766
RESTRICT
Usage
You must own the view or have the DBA privilege to use the DROP VIEW
statement.
When you drop view name, you also drop all views that have been defined in
terms of that view. You can also specify this default condition with the
CASCADE keyword.
When you use the RESTRICT keyword in the DROP VIEW statement, the drop
operation fails if any existing views are defined on view name, which would
be abandoned in the drop operation.
You can query the sysdepend system catalog table to determine which views,
if any, depend on another view.
The following statement drops the view that is named cust1:
DROP VIEW cust1
SE
You cannot use a ROLLBACK WORK statement to undo a DROP VIEW
statement. If you roll back a transaction that contains a DROP VIEW
statement, the view is not re-created, and you do not receive an error
message. ♦
SQL Statements 1-279
DROP VIEW
References
See the CREATE VIEW and DROP TABLE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of views in
Chapter 10.
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Informix Guide to SQL: Syntax
EXECUTE
EXECUTE
Use the EXECUTE statement to run a previously prepared statement or set of
statements.
Syntax
ESQL
EXECUTE
statement id
statement
id variable
Element
statement id
Purpose
Identifies an SQL statement
statement id
variable
Host variable that identifies an
SQL statement
INTO
Clause
p. 1-283
USING
Clause
p. 1-286
Restrictions
You must have defined the
statement identifier in a
previous PREPARE statement.
After you release the database
server resources (using a FREE
statement), you cannot use the
statement identifier with a
DECLARE cursor or with the
EXECUTE statement until you
prepare the statement again.
You must have defined the host
variable in a previous PREPARE
statement. The host variable
must be a character data type.
Syntax
PREPARE, p. 1-402
PREPARE, p. 1-402
Usage
The EXECUTE statement passes a prepared SQL statement to the database
server for execution. If the statement contained question mark (?)
placeholders, specific values are supplied for them before execution. Once
prepared, an SQL statement can be executed as often as needed.
SQL Statements 1-281
EXECUTE
You can execute any prepared statement. However, for stored procedures
that return more than one row, you cannot execute a prepared SELECT
statement or a prepared EXECUTE PROCEDURE statement. When you use a
prepared SELECT statement to return multiple rows of data, you can use the
DECLARE, OPEN, and FETCH cursor statements to retrieve the data rows. In
addition, you can use EXECUTE on a prepared SELECT INTO TEMP statement
to achieve the same result. If you prepare an EXECUTE PROCEDURE
statement for a procedure that returns multiple rows, you need to use the
DECLARE, OPEN, and FETCH cursor statements just as you would with a
SELECT statement.
If you create or drop a trigger after you prepared a triggering INSERT,
DELETE, or UPDATE statement, the prepared statement returns an error when
you execute it.
The following example shows an EXECUTE statement within an
INFORMIX-ESQL/C program:
EXEC SQL prepare del_1 from
'delete from customer
where customer_num = 119';
EXEC SQL execute del_1;
Scope of Statement Identifiers
A program can consist of one or more source-code files. By default, the scope
of a statement identifier is global to the program, so a statement identifier
created in one file can be referenced from another file.
In a multiple-file program, if you want to limit the scope of a statement
identifier to the file in which it is executed, you can preprocess all the files
with the -local command-line option. See your SQL API product manual for
more information, restrictions, and performance issues when you preprocess
files with the -local option.
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EXECUTE
The sqlca Record and EXECUTE
Following an EXECUTE statement, the sqlca (see your SQL API product
manual) can reflect two results:
■
The sqlca can reflect an error within the EXECUTE statement. For
example, when an UPDATE ... WHERE ... statement within a prepared
object processes zero rows, the database server sets sqlca
to 100.
■
The sqlca can also reflect the success or failure of the executed
statement.
INTO Clause
SQL Statements 1-283
EXECUTE
Element
output
descriptor
output
descriptor
variable
output
indicator
variable
output
sqlda
pointer
output
variable
name
Purpose
Quoted string that identifies a
system-descriptor area
Host variable name that
identifies the system-descriptor
area
Host variable that receives a
return code if null data is placed
in the corresponding output
variable
Restrictions
System-descriptor area must
already be allocated.
System-descriptor area must
already be allocated.
Syntax
Quoted String,
p. 1-757
Quoted String,
p. 1-757
Variable cannot be DATETIME or Variable name must
INTERVAL data type.
conform to
language-specific
rules for variable
names.
Points to an sqlda structure that You cannot begin an output
DESCRIBE, p. 1-255
defines the data type and
sqlda pointer with a dollar sign
memory location of values that ($) or a colon (:). You must use an
correspond to the question-mark sqlda structure if you are using
( ?) placeholder in a prepared
dynamic SQL statements.
statement.
Host variable whose contents
Variable must be a character
Variable name must
replace a question-mark ( ?)
data type.
conform to
placeholder in a prepared
language-specific
statement
rules for variable
names.
The INTO clause allows you to execute a prepared singleton SELECT
statement or a prepared EXECUTE PROCEDURE statement, and store the
returned values into output variables, output SQL descriptors, or output
sqlda pointers. The INTO clause provides a concise and efficient alternative
to more complicated and lengthy syntax. In addition, by placing values into
variables that can be displayed, the INTO clause simplifies and enhances your
ability to retrieve and display data values. For example, if you use the INTO
clause, you do not have to use the PREPARE, DECLARE, OPEN, and FETCH
sequence of statements to retrieve values from a table.
Important: If you execute a prepared SELECT statement that returns more than one
row of data, you receive an error message. In addition, if you prepare and declare a
statement, and then attempt to execute that statement, you receive an error message.
You cannot select a null value from a table column and place that value into an
output variable. If you know in advance that a table column contains a null value,
make sure after you select the data that you check the indicator variable that is
associated with the column to determine if the value is null.
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EXECUTE
The following list describes the procedure for using the INTO clause with the
EXECUTE statement:
1.
Declare the output variables that the EXECUTE statement uses.
2.
Use the PREPARE statement to prepare your SELECT statement or to
prepare your EXECUTE PROCEDURE statement.
3.
Use the EXECUTE statement, with the INTO clause, to execute your
SELECT statement or to execute your EXECUTE PROCEDURE
statement.
The following example shows how to use the INTO clause with an EXECUTE
statement in INFORMIX-ESQL/C:
EXEC SQL prepare sel1 from 'select fname, lname from customer
where customer_num =123';
EXEC SQL execute sel1 into :fname, :lname using :cust_num;
The following example shows how to use the INTO clause to return multiple
rows of data:
EXEC SQL BEGIN DECLARE SECTION;
int customer_num =100;
char fname[25];
EXEC SQL END DECLARE SECTION;
EXEC SQL prepare sel1 from 'select fname from customer
where customer_num=?';
for ( ;customer_num < 200; customer_num++)
{
EXEC SQL execute sel1 into :fname using customer_num;
printf("Customer number is %d\n", customer_num);
printf("Customer first name is %s\n\n", fname);
}
SQL Statements 1-285
EXECUTE
USING Clause
USING
Clause
,
storage
variable
name
USING
E/C
:
+
INDICATOR
SQL DESCRIPTOR
E/C
storage
indicator
variable
storage
indicator
variable
'storage descriptor'
storage descriptor variable
DESCRIPTOR
Element
storage
descriptor
Purpose
Quoted string that identifies a
system-descriptor area
storage
descriptor
variable
Host variable name that
identifies a system-descriptor
area
storage sqlda pointer
Restrictions
System-descriptor area must
already be allocated. Make sure
surrounding quotes are single.
System-descriptor area must
already be allocated.
Syntax
Quoted String,
p. 1-757
Variable name must
conform to
language-specific
rules for variable
names.
(1 of 2)
1-286
Informix Guide to SQL: Syntax
EXECUTE
Element
storage
indicator
variable
storage
sqlda
pointer
storage
variable
name
Purpose
Host variable that receives a
return code if null data is placed
in the corresponding data
variable. Receives truncation
information if truncation occurs.
Points to an sqlda structure that
defines the data type and
memory location of values that
correspond to the question-mark
( ?) placeholder in a prepared
statement.
Host variable whose contents
replace a question-mark ( ?)
placeholder in a prepared
statement
Restrictions
Syntax
Variable cannot be DATETIME or Variable name must
INTERVAL data type.
conform to
language-specific
rules for variable
names.
You cannot begin storage sqlda
DESCRIBE, p. 1-255
pointer with a dollar sign ($) or a
colon (:). You must use an sqlda
structure if you are using
dynamic SQL statements.
Variable must be a character
data type.
Variable name must
conform to
language-specific
rules for variable
names.
(2 of 2)
The USING clause specifies values that are to replace question-mark (?)
placeholders in the prepared statement. Providing values in the EXECUTE
statement that replace the question-mark placeholders in the prepared
statement is sometimes called parameterizing the prepared statement.
You can specify any of the following items to replace the question-mark
placeholders in a statement before you execute it:
E/C
■
A host variable name (if the number and data type of the question
marks are known at compile time)
■
A system descriptor that identifies a system
■
A descriptor that is a pointer to an sqlda structure ♦
Supplying Parameters Through Host or Program Variables
You must supply one storage variable name for each placeholder. The data
type of each variable must be compatible with the corresponding value that
the prepared statement requires.
SQL Statements 1-287
EXECUTE
The following example executes the prepared UPDATE statement in
INFORMIX-ESQL/C:
stcopy ("update orders set order_date = ? where po_num = ?", stm1);
EXEC SQL prepare statement_1 from :stm1;
EXEC SQL execute statement_1 using :order_date :po_num;
Supplying Parameters Through a System Descriptor
You can create a system-descriptor area that describes the data type and
memory location of one or more values and then specify the storage
descriptor in the USING SQL DESCRIPTOR clause of the EXECUTE statement.
Each time that the EXECUTE statement is run, the values that the systemdescriptor area describes are used to replace question-mark (?) placeholders
in the PREPARE statement.
The COUNT field corresponds to the number of dynamic parameters in the
prepared statement. The value of COUNT must be less than or equal to the
value of the occurrences that were specified when the system-descriptor area
was allocated with the ALLOCATE DESCRIPTOR statement.
For more information on system descriptors, see your SQL API product
manual.
The following examples show how to use system descriptors to execute
prepared statements in INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL,
respectively:
INFORMIX-ESQL/C
EXEC SQL execute prep_stmt using sql descriptor 'desc1';
INFORMIX-ESQL/COBOL
EXEC SQL EXECUTE PREP_STMT USING SQL DESCRIPTOR 'DESC1'
END-EXEC.
1-288
Informix Guide to SQL: Syntax
EXECUTE
Supplying INFORMIX-ESQL/C Parameters Through an sqlda Structure
You can specify the storage sqlda pointer in the USING DESCRIPTOR clause of
the EXECUTE statement. Each time the EXECUTE statement is run, the values
that the sqlda structure describes are used to replace question-mark (?) placeholders in the PREPARE statement.
For more information on the sqlda structure, see the manual for the version
of INFORMIX-ESQL/C that you are using.
The following example shows how to use an sqlda structure to execute a
prepared statement in INFORMIX-ESQL/C:
EXEC SQL execute prep_stmt using descriptor pointer2
Error Conditions with EXECUTE
In a database that is not ANSI compliant, if any statement fails to access any
rows, the database server returns (0).
ANSI
In an ANSI-compliant database, if you prepare and execute any of the
following statements, and no rows are returned, the database server returns
SQLNOTFOUND (100):
■
INSERT INTO table-name SELECT ... WHERE ...
■
SELECT INTO TEMP ... WHERE ...
■
DELETE ... WHERE
■
UPDATE ... WHERE ... ♦
In a multistatement prepare, if any statement in the preceding list fails to
access rows, in either ANSI databases or databases that are not ANSI
compliant, the database server returns SQLNOTFOUND (100).
References
See the ALLOCATE DESCRIPTOR, DEALLOCATE DESCRIPTOR, DECLARE,
EXECUTE IMMEDIATE, GET DESCRIPTOR, PREPARE, PUT, and SET
DESCRIPTOR statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of the EXECUTE
statement in Chapter 5.
SQL Statements 1-289
EXECUTE IMMEDIATE
EXECUTE IMMEDIATE
Use the EXECUTE IMMEDIATE statement to perform the functions of the
PREPARE, EXECUTE, and FREE statements.
Syntax
+
ESQL
EXECUTE IMMEDIATE
Quoted
String
p. 1-757
statement variable name
Element
statement
variable name
Purpose
Host variable whose value is a
character string that consists of
one or more SQL statements.
Restrictions
The host variable must have
been defined within the
program. The variable must be
character data type. For
additional restrictions, see
“EXECUTE IMMEDIATE and
Restricted Statements” on
page 1-291 and “Restrictions on
Allowed Statements” on
page 1-291.
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
Usage
The quoted string is a character string that includes one or more SQL
statements. The string, or the contents of statement variable name, is parsed
and executed if correct; then all data structures and memory resources are
released immediately. In the usual method of dynamic execution, these
functions are distributed among the PREPARE, EXECUTE, and FREE
statements.
The EXECUTE IMMEDIATE statement makes it easy to execute dynamically a
single simple SQL statement, which is constructed during program execution.
For example, you could obtain the name of a database from program input,
construct the DATABASE statement as a program variable, and then use
EXECUTE IMMEDIATE to execute the statement, which opens the database.
1-290
Informix Guide to SQL: Syntax
EXECUTE IMMEDIATE
EXECUTE IMMEDIATE and Restricted Statements
You cannot use the EXECUTE IMMEDIATE statement to execute the following
SQL statements.
CLOSE
CONNECT
DECLARE
DISCONNECT
EXECUTE
GET DESCRIPTOR
OPEN
PREPARE
SELECT
SET CONNECTION
EXECUTE PROCEDURE (if the
SET DESCRIPTOR
procedure returns values)
FETCH
GET DIAGNOSTICS
WHENEVER
Use a PREPARE statement to execute a dynamically constructed SELECT
statement.
Restrictions on Allowed Statements
The following restrictions apply to the statement that is contained in the
quoted string or in statement variable name:
■
The statement cannot contain a host-language comment.
■
Names of host-language variables are not recognized as such in
prepared text. The only identifiers that you can use are names
defined in the database, such as table names and columns.
■
The statement cannot reference a host variable list or a descriptor; it
must not contain any question-mark (?) placeholders, which are
allowed with a PREPARE statement.
■
The text must not include any embedded SQL statement prefix or
terminator, such as the dollar sign ($), colon (:), or the words EXEC
SQL.
SQL Statements 1-291
EXECUTE IMMEDIATE
Example of the EXECUTE IMMEDIATE Statement
The following example shows the EXECUTE IMMEDIATE statement in
INFORMIX-ESQL/C:
sprintf(cdb_text, "create database %s", usr_db_id);
EXEC SQL execute immediate :cdb_text;
References
See the EXECUTE, FREE, and PREPARE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of quick execution in
Chapter 5.
1-292
Informix Guide to SQL: Syntax
EXECUTE PROCEDURE
EXECUTE PROCEDURE
Use the EXECUTE PROCEDURE statement to execute a procedure from the
DB-Access interactive editor, an SQL API, or another stored procedure.
Syntax
+
EXECUTE
PROCEDURE
Procedure
Name
p. 1-754
(
)
,
Argument
ESQL
SPL
,
INTO
host
variable
Argument
Expression
p. 1-671
parameter name =
SELECT
Statement
(Singleton)
p. 1-459
SQL Statements 1-293
EXECUTE PROCEDURE
Element
host variable
Purpose
A host variable that receives a
returned value from a
procedure, or a list of such
variables
parameter name The name of a parameter for
which you supply an argument
to the procedure
Restrictions
If you issue an EXECUTE
PROCEDURE statement within
an SQL API, the receiving
variables must be host variables.
If you issue an EXECUTE
PROCEDURE statement within a
stored procedure, the receiving
variables must be procedure
variables. If you issue an
EXECUTE PROCEDURE statement
within a CREATE TRIGGER
statement, the receiving
variables must be column names
within the triggering table or
another table.
The parameter name must
match the parameter name that
you specified in a corresponding
CREATE PROCEDURE statement.
If you use the parameter name =
syntax for any argument in the
Syntax
The name of a host
variable must
conform to
language-specific
rules for variable
names. For the
syntax of procedure
variables, see
Expression, p. 1-671.
For the syntax of
column names, see
Identifier, p. 1-723.
Expression, p. 1-671
EXECUTE PROCEDURE
statement, you must use it for all
arguments.
Usage
The EXECUTE PROCEDURE statement invokes a procedure called Procedure
Name.
If an EXECUTE PROCEDURE statement has more arguments than the called
procedure expects, an error is returned.
If an EXECUTE PROCEDURE statement has fewer arguments than the called
procedure expects, the arguments are said to be missing. Missing arguments
are initialized to their corresponding default values if default values were
specified. (See the CREATE PROCEDURE statement on page 1-134.) This
initialization occurs before the first executable statement in the body of the
procedure.
1-294
Informix Guide to SQL: Syntax
EXECUTE PROCEDURE
If arguments are missing and do not have default values, they are initialized
to the value of UNDEFINED. An attempt to use any variable that has the value
of UNDEFINED results in an error.
Name or position, but not both, binds procedure arguments to procedure
parameters. That is, you can use parameter name = syntax for none or all of the
arguments that are specified in one EXECUTE PROCEDURE statement.
For instance, in the following example, both the procedure calls are valid for
a procedure that expects three character arguments, t, d, and n:
EXECUTE PROCEDURE add_col (t ='customer', d ='integer', n ='newint')
EXECUTE PROCEDURE add_col ('customer','newint','integer')
ESQL
If the EXECUTE PROCEDURE statement returns more than one row, it must be
enclosed within an SPL FOREACH loop or accessed through a cursor. ♦
INTO Clause
ESQL
SPL
The INTO clause specifies where the values that the procedure returns will be
stored.
The host variable list is a list of the host variables that receive the returned
values from a procedure call. A procedure that returns more than one row
must be enclosed in a cursor.
If you execute a procedure from within a stored procedure, the list contains
procedure variables.
If you execute a procedure from within a triggered action, the list contains
column names from the triggering table or another table. For information on
triggered actions, see the CREATE TRIGGER statement on page 1-192.
You cannot prepare an EXECUTE PROCEDURE statement that has an INTO
clause. See “Executing Stored Procedures Within a PREPARE Statement” on
page 1-406 for more information. ♦
References
See the CREATE PROCEDURE, DROP PROCEDURE, GRANT, and CALL
statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of creating and using
stored procedures in Chapter 12.
SQL Statements 1-295
FETCH
FETCH
Use the FETCH statement to move a cursor to a new row in the active set and
to retrieve the row values from memory.
Syntax
,
ESQL
FETCH
INTO
cursor id
+
data
variable
cursor
variable
+
NEXT
PREVIOUS
indicator
INDICATOR variable
data structure
+
PRIOR
FIRST
LAST
CURRENT
USING
row
position
RELATIVE
+
ABSOLUTE
1-296
Informix Guide to SQL: Syntax
SQL
DESCRIPTOR
'descriptor'
descriptor
variable
E/C
DESCRIPTOR
row
position
indicator
variable
sqlda
pointer
FETCH
Element
cursor id
cursor variable
data structure
data variable
descriptor
descriptor
variable
Purpose
Identifier for a cursor from
which rows are to be retrieved
Restrictions
The cursor must have been
created in an earlier DECLARE
statement and opened in an
earlier OPEN statement.
Host variable name that holds
The cursor identified in cursor
the value of cursor id
variable must have been created
in an earlier DECLARE statement
and opened in an earlier OPEN
statement.
Structure that has been declared The individual members of the
as a host variable
data structure must be matched
appropriately to the type of
values that are being fetched. If
you use a program array, you
must list both the array name
and a specific element of the
array in data structure.
Host variable that receives one The host variable must have a
value from the fetched row
data type that is appropriate for
the value that is fetched into it.
Syntax
Identifier, p. 1-723
Variable name must
conform to
language-specific
rules for variable
names.
Data-structure name
must conform to
language-specific
rules for datastructure names.
Variable name must
conform to
language-specific
rules for variable
names.
String that identifies the system- The system-descriptor area must Quoted String,
descriptor area into which you have been allocated with the
p. 1-757
ALLOCATE DESCRIPTOR
fetch the contents of a row
statement.
Host variable name that holds
The system-descriptor area that Variable name must
the value of descriptor
is identified in descriptor variable conform to
must have been allocated with
language-specific
the ALLOCATE DESCRIPTOR
rules for variable
statement.
names.
(1 of 2)
SQL Statements 1-297
FETCH
Element
indicator
variable
Purpose
Host variable that receives a
return code if null data is placed
in the corresponding data
variable
row position
sqlda pointer
Restrictions
This parameter is optional, but
use an indicator variable if the
possibility exists that the value
of data variable is null. If you
specify the indicator variable
without the INDICATOR
keyword, you cannot put a space
between data variable and
indicator variable. The rules for
placing a prefix before indicator
variable are language-specific.
See your SQL API manual for
further information on indicator
variables.
Integer value or host variable
A value of 0 for row position is
that contains an integer value.
allowed with the RELATIVE
keyword. A value of 0 fetches
The integer value gives the
position of the desired row in the the current row. The value of row
active set of rows. See “FETCH position must be 1 or higher with
the ABSOLUTE keyword.
with a Scroll Cursor” on
page 1-300 for a discussion of the
RELATIVE and ABSOLUTE
keywords and the meaning of
row position with each keyword.
Pointer to an sqlda structure that You cannot begin an sqlda
receives the values from the
pointer with a dollar sign ($) or a
fetched row
colon (:).
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
If you are using a
host variable,
variable name must
conform to
language-specific
rules for variable
names. If you are
using a literal
number, see Literal
Number, p. 1-752.
See the discussion of
sqlda structure in the
INFORMIX-ESQL/
C Programmer’s
Manual.
(2 of 2)
Usage
The FETCH statement is one of four statements that are used for queries that
return more than one row from the database. The four statements, DECLARE,
OPEN, FETCH, and CLOSE, are used in the following sequence:
1-298
1.
Declare a cursor to control the active set of rows.
2.
Open the cursor to begin execution of the query.
3.
Fetch from the cursor to retrieve the contents of each row.
Informix Guide to SQL: Syntax
FETCH
4.
Close the cursor to break the association between the cursor and the
active set.
A cursor is created as either a sequential cursor or a scroll cursor. The way the
database server creates and stores members of the active set and then fetches
rows from the active set differs depending on whether the cursor is a
sequential cursor or a scroll cursor. (See the DECLARE statement on
page 1-234 for details on the types of cursors.)
X/O
In X/Open mode, if a cursor-direction value (such as NEXT or RELATIVE) is
specified, a warning message is issued, indicating that the statement does not
conform to X/Open standards. ♦
FETCH with a Sequential Cursor
A sequential cursor can fetch only the next row in sequence from the active
set. The sole keyword option that is available to a sequential cursor is the
default value, NEXT. A sequential cursor can read through a table only once
each time it is opened. The following example in INFORMIX-ESQL/C
illustrates the use of a sequential cursor:
EXEC SQL fetch seq_curs into :fname, :lname;
When the program opens a sequential cursor, the database server processes
the query to the point of locating or constructing the first row of data. The
goal of the database server is to tie up as few resources as possible.
Because the sequential cursor can retrieve only the next row, the database
server can frequently create the active set one row at a time. On each FETCH
operation, the database server returns the contents of the current row and
locates the next row. This one-row-at-a-time strategy is not possible if the
database server must create the entire active set to determine which row is
the first row (as would be the case if the SELECT statement included an
ORDER BY clause).
SQL Statements 1-299
FETCH
FETCH with a Scroll Cursor
A scroll cursor can fetch any row in the active set, either by specifying an
absolute row position or a relative offset. Use the following keywords to
specify a particular row that you want to retrieve.
Keyword
Effect
NEXT
retrieves the next row in the active set.
PREVIOUS
retrieves the previous row in the active set.
PRIOR
is synonymous with PREVIOUS; it retrieves the previous row
in the active set.
FIRST
retrieves the first row in the active set.
LAST
retrieves the last row in the active set.
CURRENT
retrieves the current row in the active set (the same row as
returned by the preceding FETCH statement from the scroll
cursor).
RELATIVE
retrieves the nth row, relative to the current cursor position in
the active set, where row position supplies n. A negative value
indicates the nth row prior to the current cursor position. If
row position is 0, the current row is fetched.
ABSOLUTE
retrieves the nth row in the active set, where row position
supplies n. Absolute row positions are numbered from 1.
The following INFORMIX-ESQL/C examples illustrate the FETCH statement:
EXEC SQL fetch previous q_curs into :orders;
EXEC SQL fetch last q_curs into :orders;
EXEC SQL fetch relative -10 q_curs into :orders;
printf("Which row? ");
scanf("%d",row_num);
EXEC SQL fetch absolute :row_num q_curs into :orders;
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Informix Guide to SQL: Syntax
FETCH
Row Numbers
The row numbers that are used with the ABSOLUTE keyword are valid only
while the cursor is open. Do not confuse them with rowid values. A rowid
value is based on the position of a row in its table and remains valid until the
table is rebuilt. A row number for a FETCH statement is based on the position
of the row in the active set of the cursor; the next time the cursor is opened,
different rows might be selected.
How the Database Server Stores Rows
The database server must retain all the rows in the active set for a scroll
cursor until the cursor closes, because it cannot be sure which row the
program asks for next. When a scroll cursor opens, the database server implements the active set as a temporary table although it might not fill this table
immediately.
The first time a row is fetched, the database server copies it into the
temporary table as well as returning it to the program. When a row is fetched
for the second time, it can be taken from the temporary table. This scheme
uses the fewest resources in case the program abandons the query before it
fetches all the rows. Rows that are never fetched are usually not created or are
saved in a temporary table.
Specifying Where Values Go in Memory
Each value from the select list of the query or the output of the executed
procedure must be returned into a memory location. You can specify these
destinations in one of the following ways:
E/C
■
Use the INTO clause of a SELECT statement.
■
Use the INTO clause of a EXECUTE PROCEDURE statement.
■
Use the INTO clause of a FETCH statement.
■
Use a system-descriptor area.
■
Use an sqlda structure. ♦
SQL Statements 1-301
FETCH
Using the INTO Clause of SELECT
The SELECT statement that is associated with the cursor can contain an INTO
clause, which specifies the program variables that are to receive the values.
You can use this method only when the SELECT statement is written as part
of the declaration of the cursor (see the DECLARE statement on page 1-234).
In this case, the FETCH statement cannot contain an INTO clause. The
following example uses the INTO clause of the SELECT statement to specify
program variables in INFORMIX-ESQL/C:
EXEC SQL declare ord_date cursor for
select order_num, order_date, po_num
into :o_num, :o_date, :o_po;
EXEC SQL open ord_date;
EXEC SQL fetch next ord_date;
Use an indicator variable if the data that is returned from the SELECT
statement might be null. See your SQL API manual for more information
about indicator variables.
Using the INTO Clause of EXECUTE PROCEDURE
The EXECUTE PROCEDURE statement that is associated with the cursor can
contain an INTO clause, which specifies the program variables that are to
receive the values. You can use this method only when the EXECUTE
PROCEDURE statement is written as part of the cursor declaration (see the
DECLARE statement on page 1-234). In this case, the FETCH statement cannot
contain an INTO clause. The following example uses the INTO clause of the
EXECUTE PROCEDURE statement to specify program variables in
INFORMIX-ESQL/C:
EXEC SQL declare ord_date cursor for
execute procedure xx (20)
into :o_num, :o_date, :o_po;
EXEC SQL open ord_date;
EXEC SQL fetch next ord_date;
Use an indicator variable if the data that is returned from the EXECUTE
PROCEDURE statement might be null. See your SQL API manual for more
information about indicator variables.
1-302
Informix Guide to SQL: Syntax
FETCH
Using the INTO Clause of FETCH
When the SELECT statement omits the INTO clause, you must specify the
destination of the data whenever a row is fetched. The FETCH statement can
include an INTO clause to retrieve data into a set of variables. This method
lets you store different rows in different memory locations.
In the following INFORMIX-ESQL/C example, a series of complete rows is
fetched into a program array. The INTO clause of each FETCH statement
specifies an array element as well as the array name.
EXEC SQL BEGIN DECLARE SECTION;
char wanted_state[2];
short int row_count = 0;
struct customer_t{
{
int
c_no;
char
fname[15];
char
lname[15];
} cust_rec[100];
EXEC SQL END DECLARE SECTION;
main()
{
EXEC SQL connect to'stores7';
printf("Enter 2-letter state code: ");
scanf ("%s", wanted_state);
EXEC SQL declare cust cursor for
select * from customer where state = :wanted_state;
EXEC SQL open cust;
EXEC SQL fetch cust into :cust_rec[row_count];
while (SQLCODE == 0)
{
printf("\n%s %s", cust_rec[row_count].fname,
cust_rec[row_count].lname);
row_count++;
EXEC SQL fetch cust into :cust_rec[row_count];
}
printf ("\n");
EXEC SQL close cust;
EXEC SQL free cust;
}
You can fetch into a program-array element only by using an INTO clause in
the FETCH statement. When you are declaring a cursor, do not refer to an
array element within the SQL statement.
SQL Statements 1-303
FETCH
Using a System-Descriptor Area
You can use a system-descriptor area as an output variable. The keywords
USING SQL DESCRIPTOR introduce the name of the system-descriptor area
into which you fetch the contents of a row. You can then use the GET
DESCRIPTOR statement to transfer the values that the FETCH statement
returns from the system-descriptor area into host variables.
For more information, see the manual for your SQL API. The following
examples show sample FETCH USING SQL DESCRIPTOR statements in
INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL, respectively:
INFORMIX-ESQL/C
EXEC SQL fetch selcurs using sql descriptor 'desc';
INFORMIX-ESQL/COBOL
EXEC SQL FETCH SEL_CURS USING SQL DESCRIPTOR 'DESC' END-EXEC.
Using an sqlda Structure
E/C
You can use a pointer to an sqlda structure to supply destinations. This
structure contains data descriptors that specify the data type and memory
location for one selected value. For more information, see the
INFORMIX-ESQL/C Programmer’s Manual. The keywords USING
DESCRIPTOR introduce the name of the sqlda pointer structure.
When you create a SELECT statement dynamically, you cannot use an INTO
host-variable clause because you cannot name host variables in a prepared
statement. If you are certain of the number and data type of values in the
select list, you can use an INTO host-variable clause in the FETCH statement.
However, if user input generated the query, you might not be certain of the
number and data type of values that are being selected. In this case, you must
use an sqlda pointer structure, as the following list describes:
1-304
■
Use the DESCRIBE statement to fill in the sqlda structure.
■
Allocate memory to hold the data values.
■
Name the sqlda structure in the FETCH statement.
Informix Guide to SQL: Syntax
FETCH
The following example shows a sample FETCH USING DESCRIPTOR
statement in INFORMIX-ESQL/C:
EXEC SQL fetch selcurs using descriptor pointer2;
♦
Fetching a Row for Update
The FETCH statement does not ordinarily lock a row that is fetched. Thus,
another process can modify (update or delete) the fetched row immediately
after your program receives it. A fetched row is locked in the following cases:
ANSI
■
When you set the isolation level to Repeatable Read, each row you
fetch is locked with a read lock to keep it from changing until the cursor closes or the current transaction ends. Other programs can also
read the locked rows.
■
When you set the isolation level to Cursor Stability, the current row
is locked.
■
In an ANSI-compliant database, an isolation level of Repeatable
Read is the default; you can set it to something else. ♦
■
When you are fetching through an update cursor (one that is
declared FOR UPDATE), each row you fetch is locked with a
promotable lock. Other programs can read the locked row, but no
other program can place a promotable or write lock; therefore, the
row is unchanged if another user tries to modify it using the WHERE
CURRENT OF clause of UPDATE or DELETE statement.
When you modify a row, the lock is upgraded to a write lock and remains
until the cursor is closed or the transaction ends. If you do not modify it, the
lock might or might not be released when you fetch another row, depending
on the isolation level you have set. The lock on an unchanged row is released
as soon as another row is fetched, unless you are using Repeatable Read
isolation (see the SET ISOLATION statement on page 1-575).
Important: You can hold locks on additional rows even when Repeatable Read
isolation is not in use or is unavailable. Update the row with unchanged data to hold
it locked while your program is reading other rows. You must evaluate the effect of
this technique on performance in the context of your application, and you must be
aware of the increased potential for deadlock.
SQL Statements 1-305
FETCH
When you use explicit transactions, be sure that a row is both fetched and
modified within a single transaction; that is, both the FETCH statement and
the subsequent UPDATE or DELETE statement must fall between a BEGIN
WORK statement and the next COMMIT WORK statement.
SE
You cannot set the database isolation level for INFORMIX-SE. ♦
Checking the Result of FETCH
You can use the GET DIAGNOSTICS statement to check the result of each
FETCH statement. Examine the RETURNED_SQLSTATE field of the GET
DIAGNOSTICS statement to check if the field contains the value 02000.
If a row is returned successfully, the RETURNED_SQLSTATE field of GET
DIAGNOSTICS contains the value 00000. If no row is found, the preprocessor
sets the SQLSTATE code to 02000, which indicates no data found, and the
current row is unchanged. Five conditions set the SQLSTATE code to 02000,
indicating no data found, as the following list describes:
■
The active set contains no rows.
■
You issue a FETCH NEXT statement when the cursor points to the last
row in the active set or points past it.
■
You issue a FETCH PRIOR or FETCH PREVIOUS statement when the
cursor points to the first row in the active set.
■
You issue a FETCH RELATIVE n statement when no nth row exists in
the active set.
■
You issue a FETCH ABSOLUTE n statement when no nth row exists in
the active set.
See the GET DIAGNOSTICS statement in this manual for more information.
You can also use SQLCODE of sqlca to determine the same results. See the
Informix Guide to SQL: Tutorial for further information about SQLCODE of
sqlca.
1-306
Informix Guide to SQL: Syntax
FETCH
References
See the ALLOCATE DESCRIPTOR, CLOSE, DEALLOCATE DESCRIPTOR,
DECLARE, DESCRIBE, GET DESCRIPTOR, OPEN, PREPARE, and SET
DESCRIPTOR statements in this manual for further information about using
the FETCH statement with dynamic management statements.
In the Informix Guide to SQL: Tutorial, see the discussion of the FETCH
statement in Chapter 5.
For further information about error checking and the system-descriptor area,
see your SQL API manual.
SQL Statements 1-307
FLUSH
FLUSH
Use the FLUSH statement to force rows that a PUT statement buffered to be
written to the database.
Syntax
ESQL
+
FLUSH
cursor
id
cursor
variable
Element
cursor id
Purpose
Identifies a cursor
cursor variable
Host variable that identifies a
cursor
Restrictions
A DECLARE statement must
have previously created the
cursor.
Host variable must be a
character data type. A DECLARE
statement must have previously
created the cursor.
Syntax
Identifier, p. 1-723
Variable name must
conform to
language-specific
rules for variable
names.
Usage
The PUT statement adds a row to a buffer, and the buffer is written to the
database when it is full. Use the FLUSH statement to force the insertion when
the buffer is not full.
If the program terminates without closing the cursor, the buffer is left
unflushed. Rows placed into the buffer since the last flush are lost. Do not
expect the end of the program to close the cursor and flush the buffer.
The following example shows a FLUSH statement:
FLUSH icurs
1-308
Informix Guide to SQL: Syntax
FLUSH
Error Checking FLUSH Statements
The sqlca structure contains information on the success of each FLUSH
statement and the number of rows that are inserted successfully. The result of
each FLUSH statement is contained in the fields of the sqlca, as the following
table shows.
ESQL/C
ESQL/COBOL
sqlca.sqlcode,
SQLCODE of SQLCA
SQLCODE
sqlca.sqlerrd[2]
SQLERRD[3] OF SQLCA
When you use data buffering with an insert cursor, you do not discover
errors until the buffer is flushed. For example, an input value that is incompatible with the data type of the column for which it is intended is discovered
only when the buffer is flushed. When an error is discovered, rows in the
buffer that are located after the error are not inserted; they are lost from
memory.
The SQLCODE field is set either to an error code or to zero if no error occurs.
The third element of the sqlerrd array is set to the number of rows that are
successfully inserted into the database:
■
If a block of rows is successfully inserted into the database,
SQLCODE is set to zero and sqlerrd to the count of rows.
■
If an error occurs while the FLUSH statement is inserting a block of
rows, SQLCODE shows which error, and sqlerrd contains the
number of rows that were successfully inserted. (Uninserted rows
are discarded from the buffer.)
Tip: When you encounter an SQLCODE error, a corresponding SQLSTATE error
value might exist. Check the GET DIAGNOSTICS statement for information about
getting the SQLSTATE value and using the GET DIAGNOSTICS statement to
interpret the SQLSTATE value.
SQL Statements 1-309
FLUSH
Counting Total and Pending Rows
To count the number of rows actually inserted into the database as well as the
number not yet inserted, perform the following steps:
1.
Prepare two integer variables, for example, total and pending.
2.
When the cursor opens, set both variables to 0.
3.
Each time a PUT statement executes, increment both total and
pending.
4.
Whenever a FLUSH statement executes or the cursor is closed,
subtract the third field of the SQLERRD array from pending.
References
See the CLOSE, DECLARE, OPEN, and PUT statements in this manual.
For information about the sqlca structure, see your SQL API manual.
In the Informix Guide to SQL: Tutorial, see the discussion of FLUSH in
Chapter 6.
1-310
Informix Guide to SQL: Syntax
FREE
FREE
The FREE statement releases resources that are allocated to a prepared
statement or to a cursor.
Syntax
ESQL
+
FREE
cursor id
cursor
variable
statement
id
statement
id variable
Element
cursor id
Purpose
Identifies a cursor
cursor variable
Host variable that identifies a
cursor
statement id
statement id
variable
Restrictions
A DECLARE statement must
have previously created the
cursor.
Variable must be a character data
type. Cursor must have been
previously created by a
DECLARE statement.
Syntax
Identifier, p. 1-723
Variable name must
conform to
language-specific
rules for variable
names
Identifies an SQL statement
The statement identifier must be PREPARE, p. 1-402
defined in a previous PREPARE
statement. After you release the
database-server resources, you
cannot use the statement
identifier with a DECLARE
cursor or with the EXECUTE
statement until you prepare the
statement again.
A host variable that identifies an This variable must be defined in PREPARE, p. 1-402
SQL statement
a previous PREPARE statement.
Variable must be a character
data type.
SQL Statements 1-311
FREE
Usage
The FREE statement releases the resources that were allocated for a prepared
statement or a declared cursor in the application-development tool and the
database server. Resources are allocated when you prepare a statement or
when you open a cursor (see the DECLARE and OPEN statements on pages
1-234 and 1-390, respectively.)
The amount of available memory in the system limits the total number of
open cursors and prepared statements that are allowed at one time in one
process. Use FREE statement id or FREE statement id variable to release the
resources that a prepared statement holds; use FREE cursor id or FREE cursor
variable to release resources that a cursor holds.
Freeing a Statement
If you prepared a statement (but did not declare a cursor for it), FREE
statement id (or statement id variable) releases the resources in both the
application development tool and the database server.
If you declared a cursor for a prepared statement, FREE statement id (or
statement id variable) releases only the resources in the application development tool; the cursor can still be used. The resources in the database server
are released only when you free the cursor.
After you free a statement, you cannot execute it or declare a cursor for it
until you prepare it again.
The following INFORMIX-ESQL/C example shows the sequence of statements
that is used to free an implicitly prepared statement:
EXEC SQL prepare sel_stmt from 'select * from orders';
.
.
.
EXEC SQL free sel_stmt;
1-312
Informix Guide to SQL: Syntax
FREE
The following INFORMIX-ESQL/C example shows the sequence of statements
that are used to release the resources of an explicitly prepared statement. The
first FREE statement in this example frees the cursor. The second FREE
statement in this example frees the prepared statement.
sprintf(demoselect, "%s %s",
"select * from customer ",
"where customer_num between 100 and 200");
EXEC SQL prepare sel_stmt from :demoselect;
EXEC SQL declare sel_curs cursor for sel_stmt;
EXEC SQL open sel_curs;
.
.
.
EXEC SQL close sel_curs;
EXEC SQL free sel_curs;
EXEC SQL free sel_stmt;
Freeing a Cursor
If you declared a cursor for a prepared statement, freeing the cursor releases
only the resources in the database server. To release the resources for the
statement in the application-development tool, use FREE statement id (or
statement id variable).
If a cursor is not declared for a prepared statement, freeing the cursor releases
the resources in both the application-development tool and the database
server.
After a cursor is freed, it cannot be opened until it is declared again. The
cursor should be explicitly closed before it is freed.
For an example of a FREE statement that frees a cursor, see the second
example in “Freeing a Statement” on page 1-312.
References
See the CLOSE, DECLARE, EXECUTE, EXECUTE IMMEDIATE, and PREPARE
statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of the FREE statement
in Chapter 5.
SQL Statements 1-313
GET DESCRIPTOR
GET DESCRIPTOR
Use the GET DESCRIPTOR statement to accomplish the following separate
tasks:
■
Determine how many values are described in a system-descriptor
area by retrieving the value in the COUNT field.
■
Determine the characteristics of each column or expression that is
described in the system-descriptor area.
■
Copy a value from the system-descriptor area into a host variable
after a FETCH statement.
Syntax
+
ESQL
GET DESCRIPTOR
'descriptor'
host variable = COUNT
,
descriptor
variable
VALUE
item
number
variable
Described
Item Info
field host
variable
=
TYPE
LENGTH
PRECISION
SCALE
NULLABLE
INDICATOR
NAME
DATA
ITYPE
IDATA
ILENGTH
1-314
item
number
Informix Guide to SQL: Syntax
Described
Item Info
GET DESCRIPTOR
Element
descriptor
descriptor
variable
field host
variable
host variable
item number
item number
variable
Purpose
A quoted string that identifies a
system-descriptor area from
which information is to be
obtained
An embedded variable name
that holds the value of descriptor
Restrictions
Syntax
The system-descriptor area must Quoted String,
have been allocated in an
p. 1-757
ALLOCATE DESCRIPTOR
statement.
The system-descriptor area
identified in descriptor variable
must have been allocated in an
The name of the
embedded variable
must conform to
ALLOCATE DESCRIPTOR
language-specific
statement.
rules for variable
names.
The name of a host variable that The field host variable must be an The name of the field
receives the contents of the
appropriate type to receive the host variable must
specified field from the system- value of the specified field from conform to
descriptor area
the system-descriptor area
language-specific
rules for variable
names.
The name of a host variable that The host variable must be an
The name of the host
indicates how many values are integer data type.
variable must
described in the systemconform to
descriptor area
language-specific
rules for variable
names.
An unsigned integer that repre- The value of item number must be Literal Number,
sents one of the occurrences
greater than zero and less than p. 1-752
(item descriptors) in the system- the number of occurrences that
descriptor area
were specified when the systemdescriptor area was allocated
with the ALLOCATE
DESCRIPTOR statement.
The name of a host variable that The item number variable must be The name of the item
holds the value of item number
an integer data type.
number variable must
conform to
language-specific
rules for variable
names.
SQL Statements 1-315
GET DESCRIPTOR
Usage
If an error occurs during the assignment to any identified host variable, the
contents of the host variable are undefined.
The role and contents of each field in a system-descriptor area are described
in the SQL API manuals.
The GET DESCRIPTOR statement can be used in EXECUTE PROCEDURE
statements, which have been described with the USING SQL DESCRIPTOR
parameter.
The host variables that are used in the GET DESCRIPTOR statement must be
declared in the BEGIN DECLARE SECTION of a SQL API program. See your
SQL API manual for specifics.
Using the COUNT Keyword
Use the COUNT keyword to determine how many values are described in the
system-descriptor area.
The following INFORMIX-ESQL/C example shows how to use a GET
DESCRIPTOR statement with a host variable to determine how many values
are described in the system-descriptor area called desc1:
main()
{
EXEC SQL BEGIN DECLARE SECTION;
int h_count;
EXEC SQL END DECLARE SECTION;
EXEC SQL allocate descriptor 'desc1' with max occurrences 20;
/* This section of program would prepare a SELECT or INSERT
* statement into the s_id statement id.
*/
EXEC SQL describe s_id using sql descriptor 'desc1';
EXEC SQL get descriptor 'desc1' :h_count = count;
...
}
1-316
Informix Guide to SQL: Syntax
GET DESCRIPTOR
VALUE Clause
Use the VALUE clause to obtain information about a described column or
expression or to retrieve values that the database server returns.
The item number must be greater than zero and less than the number of
occurrences that were specified when the system-descriptor area was
allocated using ALLOCATE DESCRIPTOR.
Using the VALUE Clause After a DESCRIBE
After you describe a SELECT, EXECUTE PROCEDURE, or INSERT statement,
the characteristics of each column or expression in the select list of the SELECT
statement, the characteristics of the values returned by the EXECUTE
PROCEDURE statement, or the characteristics of each column in the INSERT
statement are returned to the system-descriptor area. Each value in the
system-descriptor area describes the characteristics of one returned column
or expression. Each field and its possible contents are described in your SQL
API manuals.
The following INFORMIX-ESQL/C example shows how to use a GET
DESCRIPTOR statement to obtain data type information from the demodesc
system-descriptor area:
EXEC SQL get descriptor 'demodesc' value :index
:type = TYPE,
:len = LENGTH,
:name = NAME;
printf("Column %d: type = %d, len = %d, name = %s\n",
index, type, len, name);
The value that the database server returns into the TYPE field is a defined
integer. To evaluate the data type that is returned, test for a specific integer
value. The codes for the TYPE field are listed in the manual for your SQL API.
For additional information about integer data type values, see page 1-544.
X/O
In X/Open mode, the X/Open code is returned to the TYPE field. You cannot
mix the two modes because errors can result. For example, if a particular data
type is not defined under X/Open mode but is defined for Informix products,
executing a GET DESCRIPTOR statement can result in an error.
In X/Open mode, a warning message appears if ILENGTH, IDATA, or ITYPE is
used. It indicates that these fields are not standard X/Open fields for a
system-descriptor area.
SQL Statements 1-317
GET DESCRIPTOR
For more information about TYPE, ILENGTH, IDATA, and ITYPE, see the
related dynamic management chapter in the appropriate Informix SQL API
programmer’s manual. For more information about programming in
X/Open mode, see the preprocessing and compilation syntax in the
appropriate Informix SQL API programmer’s manual. ♦
If the TYPE of a fetched value is DECIMAL or MONEY, the database server
returns the precision and scale information for a column into the PRECISION
and SCALE fields after a DESCRIBE statement is executed. If the TYPE is not
DECIMAL or MONEY, the SCALE and PRECISION fields are undefined.
Using the VALUE Clause After a FETCH
Each time your program fetches a row, it must copy the fetched value into
host variables so that the data can be used. To accomplish this task, use a GET
DESCRIPTOR statement after each fetch of each value in the select list. If three
values exist in the select list, you need to use three GET DESCRIPTOR statements after each fetch (assuming you want to read all three values). The item
numbers for each of the three GET DESCRIPTOR statements are 1, 2, and 3.
The following INFORMIX-ESQL/C example shows how you can copy data
from the DATA field into a host variable (result) after a fetch. For this
example, it is predetermined that all returned values are the same data type.
EXEC SQL get descriptor 'demodesc' :desc_count = count;
.
.
.
EXEC SQL fetch democursor using sql descriptor 'demodesc';
for (i = 1; i <= desc_count; i++)
{
if (sqlca.sqlcode != 0) break;
EXEC SQL get descriptor 'demodesc' value :i :result = DATA;
printf("%s ", result);
}
printf("\n");
1-318
Informix Guide to SQL: Syntax
GET DESCRIPTOR
The following INFORMIX-ESQL/COBOL example shows how you can copy
data from the DATA field into host variables after a fetch. The first GET
DESCRIPTOR statement uses a literal item number; the second GET
DESCRIPTOR statement uses a host variable to hold the item number.
EXEC SQL BEGIN DECLARE SECTION END-EXEC.
01 COUNT
SQLINT.
01 ITEMNO
SQLINT.
01 TYPE
SQLINT.
01 LENGTH
SQLINT.
01 LONGVAL SQLINT.
01 CHVAL
SQLCHAR(21).
EXEC SQL END DECLARE SECTION END-EXEC.
EXEC SQL GET DESCRIPTOR 'desc1' VALUE 1
:TYPE = TYPE, :LENGTH = LENGTH, :CHVAL = DATA
END-EXEC.
MOVE 2 TO ITEMNO.
EXEC SQL GET DESCRIPTOR 'desc1' VALUE :ITEMNO.
:TYPE = TYPE, :LONGVAL = DATA
END-EXEC.
Fetching a Null Value
When you use GET DESCRIPTOR after a fetch, and the fetched value is null,
the INDICATOR field is set to -1 (NULL). The value of DATA is undefined if
INDICATOR indicates a null value. The host variable into which DATA is
copied has an unpredictable value.
Using LENGTH or ILENGTH
If your DATA or IDATA field contains a character string, you must specify a
value for LENGTH. If you specify LENGTH=0, LENGTH is automatically set to
the maximum length of the string. The DATA or IDATA field might contain a
literal character string or a character string that is derived from a character
variable of CHAR or VARCHAR data type. This provides a method to
determine dynamically the length of a string in the DATA or IDATA field.
If a DESCRIBE statement precedes a GET DESCRIPTOR statement, LENGTH is
automatically set to the maximum length of the character field that is
specified in your table.
This information is identical for ILENGTH. Use ILENGTH when you create a
dynamic program that does not comply with the X/Open standard.
SQL Statements 1-319
GET DESCRIPTOR
References
See the ALLOCATE DESCRIPTOR, DEALLOCATE DESCRIPTOR, DECLARE,
DESCRIBE, EXECUTE, FETCH, OPEN, PREPARE, PUT, and SET DESCRIPTOR
statements in this manual for more information about using dynamic SQL
statements.
For more information about the system-descriptor area, see your SQL API
manual.
1-320
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
GET DIAGNOSTICS
Use the GET DIAGNOSTICS statement to return diagnostic information about
executing an SQL statement. The GET DIAGNOSTICS statement uses one of
two clauses, as described in the following list:
■
The Statement clause determines count and overflow information
about errors and warnings generated by the most recent SQL
statement.
■
The EXCEPTION clause provides specific information about errors
and warnings generated by the most recent SQL statement.
Syntax
+
ESQL
GET DIAGNOSTICS
Statement
Clause
p. 1-327
EXCEPTION
Clause
p. 1-329
Usage
The GET DIAGNOSTICS statement retrieves selected status information from
the diagnostics area and retrieves either count and overflow information or
information on a specific exception.
The GET DIAGNOSTICS statement never changes the contents of the
diagnostics area.
Using the SQLSTATE Error Status Code
When an SQL statement executes, an error status code is automatically
generated. This code represents success, failure, warning, or no data
found. This error status code is stored in a variable called SQLSTATE.
SQL Statements 1-321
GET DIAGNOSTICS
Class and Subclass Codes
The SQLSTATE status code is a a five-character string that can contain only
digits and capital letters.
The first two characters of the SQLSTATE status code indicate a class. The last
three characters of the SQLSTATE code indicate a subclass. Figure 1-3 shows
the structure of the SQLSTATE code. This example uses the value 08001,
where 08 is the class code and 001 is the subclass code. The value 08001
represents the error unable to connect with database environment.
0
8
Class
code
0
0
Figure 1-3
The Structure of the
SQLSTATE Code
1
Subclass code
The following table is a quick reference for interpreting class code values.
SQLSTATE Class Code Value
Outcome
00
Success
01
Success with warning
02
No data found
> 02
Error or warning
Support for ANSI Standards
All status codes returned to the SQLSTATE variable are ANSI compliant
except in the following cases:
1-322
■
SQLSTATE codes with a class code of 01 and a subclass code that
begins with a I are Informix-specific warning messages.
■
SQLSTATE codes with a class code of IX and any subclass code are
Informix-specific error messages.
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
■
SQLSTATE codes whose class code begins with a digit in the range 5
to 9 or with a capital letter in the range I to Z indicate conditions that
are currently undefined by ANSI. The only exception is that
SQLSTATE codes whose class code is IX are Informix-specific error
messages.
List of SQLSTATE Codes
The following table describes the class codes, subclass codes, and the
meaning of all valid warning and error codes associated with the SQLSTATE
error status code.
Class
Subclass
Meaning
00
000
Success
01
000
Success with warning
01
002
Disconnect error. Transaction rolled back
01
003
Null value eliminated in set function
01
004
String data, right truncation
01
005
Insufficient item descriptor areas
01
006
Privilege not revoked
01
007
Privilege not granted
01
I01
Database has transactions
01
I03
ANSI-compliant database selected
01
I04
INFORMIX-OnLine database selected
01
I05
Float to decimal conversion has been used
01
I06
Informix extension to ANSI-compliant standard syntax
01
I07
UPDATE/DELETE statement does not have a WHERE clause
01
I08
An ANSI keyword has been used as a cursor name
01
I09
Number of items in the select list is not equal to the number in
the into list
01
I10
Database server running in secondary mode
01
I11
Dataskip is turned on
02
000
No data found
(1 of 4)
SQL Statements 1-323
GET DIAGNOSTICS
Class
Subclass
Meaning
07
000
Dynamic SQL error
07
001
USING clause does not match dynamic parameters
07
002
USING clause does not match target specifications
07
003
Cursor specification cannot be executed
07
004
USING clause is required for dynamic parameters
07
005
Prepared statement is not a cursor specification
07
006
Restricted data type attribute violation
07
008
Invalid descriptor count
07
009
Invalid descriptor index
08
000
Connection exception
08
001
Server rejected the connection
08
002
Connection name in use
08
003
Connection does not exist
08
004
Client unable to establish connection
08
006
Transaction rolled back
08
007
Transaction state unknown
08
S01
Communication failure
0A
000
Feature not supported
0A
001
Multiple server transactions
21
000
Cardinality violation
21
S01
Insert value list does not match column list
21
S02
Degree of derived table does not match column list
(2 of 4)
1-324
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
Class
Subclass
Meaning
22
000
Data exception
22
001
String data, right truncation
22
002
Null value, no indicator parameter
22
003
Numeric value out of range
22
005
Error in assignment
22
027
Data exception trim error
22
012
Division by zero
22
019
Invalid escape character
22
024
Unterminated string
22
025
Invalid escape sequence
23
000
Integrity constraint violation
24
000
Invalid cursor state
25
000
Invalid transaction state
2B
000
Dependent privilege descriptors still exist
2D
000
Invalid transaction termination
26
000
Invalid SQL statement identifier
2E
000
Invalid connection name
28
000
Invalid user-authorization specification
33
000
Invalid SQL descriptor name
34
000
Invalid cursor name
35
000
Invalid exception number
37
000
Syntax error or access violation in PREPARE or EXECUTE
IMMEDIATE
3C
000
Duplicate cursor name
40
000
Transaction rollback
40
003
Statement completion unknown
(3 of 4)
SQL Statements 1-325
GET DIAGNOSTICS
Class
Subclass
Meaning
42
000
Syntax error or access violation
S0
000
Invalid name
S0
001
Base table or view table already exists
S0
002
Base table not found
S0
011
Index already exists
S0
021
Column already exists
S1
001
Memory allocation failure
IX
000
Informix reserved error message
(4 of 4)
Using SQLSTATE in Applications
You can use a variable, called SQLSTATE, that you do not have to declare in
your program. SQLSTATE contains the error code that is essential for error
handling, which is generated every time your program executes an SQL
statement. SQLSTATE is created automatically. You can examine the
SQLSTATE variable to determine whether an SQL statement was successful.
If the SQLSTATE variable indicates that the statement failed, you can execute
a GET DIAGNOSTICS statement to obtain additional error information.
For an example of how to use an SQLSTATE variable in a program, see “Using
GET DIAGNOSTICS for Error Checking” on page 1-336.
In Chapter 5 of the Informix Guide to SQL: Tutorial, see the discussion about
error-code handling. In addition, refer to the error-handling chapter of your
SQL API manual.
1-326
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
The Statement Clause
,
st_var =
MORE
NUMBER
ROW_COUNT
Element
st_var
Purpose
Restrictions
Host variable that receives status Data type must match that of the
information about the most
requested field.
recent SQL statement. Receives
information for the specified
status field name.
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
When retrieving count and overflow information, GET DIAGNOSTICS can
deposit the values of the three statement fields into corresponding host
variable. The host-variable data type must be the same as that of the
requested field. These three fields are represented by the following
keywords.
Field Name
Keyword
Field
Data Type
Field
Contents
ESQL/C
Host Variable
Data Type
ESQL/COBOL
Host Variable
Data Type
MORE
Character
Y or N
char[2]
PIC X(1)
NUMBER
Integer
1 to 35,000
int
PIC S9(9)
ROW_COUNT
Integer
0 to 999,999,999
int
PIC S9(9)
SQL Statements 1-327
GET DIAGNOSTICS
The EXCEPTION Clause
,
EXCEPTION
except_num
en_var
ex_var
=
CLASS_ORIGIN
CONNECTION_ALIAS
MESSAGE_LENGTH
MESSAGE_TEXT
RETURNED_SQLSTATE
SERVER_NAME
SUBCLASS_ORIGIN
Element
en_var
Purpose
Host variable that specifies an
exception number for a GET
DIAGNOSTICS statement
Restrictions
Variable must contain an integer
value limited to a range from 1 to
35,000. Variable data type must
be INT or SMALLINT.
except_num
Literal integer value that
specifies the exception number
for a GET DIAGNOSTICS
statement. The except_num literal
indicates one of the exception
values from the number of
exceptions returned by the
NUMBER field in the Statement
clause.
Host variable that you declare,
which receives EXCEPTION
information about the most
recent SQL statement. Receives
information for a specified
exception field name.
Integer value is limited to a
range from 1 to 35,000.
ex_var
Syntax
Variable name must
conform to
language-specific
rules for variable
names.
Literal Number,
p. 1-752
Data type must match that of the Variable name must
requested field.
conform to
language-specific
rules for variable
names.
SQL Statements 1-329
GET DIAGNOSTICS
When retrieving exception information, GET DIAGNOSTICS deposits the
values of each of the seven fields into corresponding host variables. These
fields are located in the diagnostics area and are derived from an exception
raised by the most recent SQL statement.
The host-variable data type must be the same as that of the requested field.
The seven exception information fields are represented by the keywords
described in the following table.
Field Name
Keyword
Field
Data Type
Field
Contents
ESQL/C Host
Variable
Data Type
ESQL/COBOL
Host Variable
Data Type
RETURNED_SQLSTATE
Character
SQLSTATE
char[6]
PIC X(5)
value
CLASS_ORIGIN
Character
String
char[255]
PIC X(254)
SUBCLASS_ORIGIN
Character
String
char[255]
PIC X(254)
MESSAGE_TEXT
Character
String
char[255]
PIC X(254)
MESSAGE_LENGTH
Integer
Numeric
value
int
PIC 9(4)
COMP-5
SERVER_NAME
Character
String
char[255]
PIC X(254)
CONNECTION_NAME
Character
String
char[255]
PIC X(254)
The application specifies the exception by number, using either an unsigned
integer or an integer host variable (an exact numeric with a scale of 0). An
exception with a value of 1 corresponds to the SQLSTATE value set by the
most recent SQL statement other than GET DIAGNOSTICS. The association
between other exception numbers and other exceptions raised by that SQL
statement is undefined. Thus, no set order exists in which the diagnostic area
can be filled with exception values. You always get at least one exception,
even if the SQLSTATE value indicates success.
If an error occurs within the GET DIAGNOSTICS statement (that is, if an illegal
exception number is requested), the Informix internal SQLCODE and
SQLSTATE variables are set to the value of that exception. In addition, the
GET DIAGNOSTICS fields are undefined.
1-330
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
Using the RETURNED_SQLSTATE Keyword
Use the RETURNED_SQLSTATE keyword to determine the SQLSTATE value
that describes the exception.
Using the CLASS_ORIGIN Keyword
Use the CLASS_ORIGIN keyword to retrieve the class portion of the
RETURNED_SQLSTATE value. If the International Standards Organization
(ISO) standard defines the class, the value of CLASS_ORIGIN is equal to ISO
9075. Otherwise, the value of CLASS_ORIGIN is defined by Informix and
cannot be ISO 9075. ANSI SQL and ISO SQL are synonymous.
Using the SUBCLASS_ORIGIN Keyword
Use the SUBCLASS_ORIGIN keyword to define the source of the subclass
portion of the RETURNED_SQLSTATE value. If the ISO international standard
defines the subclass, the value of SUBCLASS_ORIGIN is equal to ISO 9075.
Using the MESSAGE_TEXT Keyword
Use the MESSAGE_TEXT keyword to determine the message text of the
exception (for example, an error message).
Using the MESSAGE_LENGTH Keyword
Use the MESSAGE_LENGTH keyword to determine the length of the current
MESSAGE_TEXT string.
Using the SERVER_NAME Keyword
Use the SERVER_NAME keyword to determine the name of the database
server associated with the actions of a CONNECT or DATABASE statement.
SQL Statements 1-331
GET DIAGNOSTICS
When the SERVER_NAME Field Is Updated
The GET DIAGNOSTICS statement updates the SERVER_NAME field when the
following situations occur:
■
A CONNECT statement successfully executes.
■
A SET CONNECTION statement successfully executes.
■
A DISCONNECT statement successfully executes at the current
connection.
■
A DISCONNECT ALL statement fails.
When the SERVER_NAME Field Is Not Updated
The SERVER_NAME field is not updated when:
■
a CONNECT statement fails.
■
a DISCONNECT statement fails (this does not include the
DISCONNECT ALL statement).
■
a SET CONNECTION statement fails.
The SERVER_NAME field retains the value set in the previous SQL statement.
If any of the preceding conditions occur on the first SQL statement that
executes, the SERVER_NAME field is blank.
1-332
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
The Contents of the SERVER_NAME Field
The SERVER_NAME field contains different information after you execute the
following statements.
Executed Statement
SERVER_NAME Field Contents
CONNECT
It contains the name of the database server to which you
connect or fail to connect. Field is blank if you do not have
a current connection or if you make a default connection.
SET CONNECTION
It contains the name of the database server to which you
switch or fail to switch.
DISCONNECT
It contains the name of the database server from which
you disconnect or fail to disconnect. If you disconnect and
then you execute a DISCONNECT statement for a
connection that is not current, the SERVER_NAME field
remains unchanged.
DISCONNECT ALL
It sets the field to blank if the statement executes successfully. If the statement does not execute successfully, the
SERVER_NAME field contains the names of all the
database servers from which you did not disconnect.
However, this information does not mean that the
connection still exists.
If the CONNECT statement is successful, the SERVER_NAME field is set to one
of the following values:
■
The INFORMIXSERVER value if the connection is to a default
database server (that is, the CONNECT statement does not list a
database server).
■
The name of the specific database server if the connection is to a
specific database server.
The DATABASE Statement
When you execute a DATABASE statement, the SERVER_NAME field contains
the name of the server on which the database resides.
SQL Statements 1-333
GET DIAGNOSTICS
Using the CONNECTION_NAME Keyword
Use the CONNECTION_NAME keyword to specify a name for the connection
used in your CONNECT or DATABASE statements.
When the CONNECTION_NAME Keyword Is Updated
GET DIAGNOSTICS updates the CONNECTION_NAME field when the
following situations occur:
■
A CONNECT statement successfully executes.
■
A SET CONNECTION statement successfully executes.
■
A DISCONNECT statement successfully executes at the current
connection. GET DIAGNOSTICS fills the CONNECTION_NAME field
with blanks because no current connection exists.
■
A DISCONNECT ALL statement fails.
When CONNECTION_NAME Is Not Updated
The CONNECTION_NAME field is not updated when the following situations
occur:
■
A CONNECT statement fails.
■
A DISCONNECT statement fails (this does not include the
DISCONNECT ALL statement).
■
A SET CONNECTION statement fails.
The CONNECTION_NAME field retains the value set in the previous SQL
statement. If any of the preceding conditions occur on the first SQL statement
that executes, the CONNECTION_NAME field is blank.
1-334
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
The Contents of the CONNECTION_NAME Field
The CONNECTION_NAME field contains different information after you
execute the following statements.
Executed Statement
CONNECTION_NAME Field Contents
CONNECT
It contains the name of the connection, specified in the
CONNECT statement, to which you connect or fail to
connect. The field is blank if you do not have a current
connection or if you make a default connection.
SET CONNECTION
It contains the name of the connection, specified in the
CONNECT statement, to which you switch or fail to switch.
DISCONNECT
It contains the name of the connection, specified in the
CONNECT statement, from which you disconnect or fail to
disconnect. If you disconnect, and then you execute a
DISCONNECT statement for a connection that is not current,
the CONNECTION_NAME field remains unchanged.
DISCONNECT ALL
The CONNECTION_NAME field is blank if the statement
executes successfully. If the statement does not execute
successfully, the CONNECTION_NAME field contains the
names of all the connections, specified in your CONNECT
statement, from which you did not disconnect. However,
this information does not mean that the connection still
exists.
If the CONNECT is successful, the CONNECTION_NAME field is set to the
following values:
■
The name of the database environment as specified in the CONNECT
statement if the CONNECT does not include the AS clause
■
The name of the connection (identifier after the AS keyword) if the
CONNECT includes the AS clause
The DATABASE Statement
When you execute a DATABASE statement, the CONNECTION_NAME field is
blank.
SQL Statements 1-335
GET DIAGNOSTICS
Using GET DIAGNOSTICS for Error Checking
The GET DIAGNOSTICS statement returns information held in various fields
of the diagnostic area. For each field in the diagnostic area that you want to
access, you must supply a host variable with a compatible data type.
The following examples illustrate using the GET DIAGNOSTICS statement to
display error information. The first example shows an ESQL/C error display
routine called disp_sqlstate_err().
void disp_sqlstate_err()
{
int j;
EXEC SQL BEGIN DECLARE SECTION;
int exception_count;
char overflow[2];
int exception_num=1;
char class_id[255];
char subclass_id[255];
char message[255];
int messlen;
char sqlstate_code[6];
int i;
EXEC SQL END DECLARE SECTION;
printf("---------------------------------");
printf("-------------------------\n");
printf("SQLSTATE: %s\n",SQLSTATE);
printf("SQLCODE: %d\n", SQLCODE);
printf("\n");
EXEC SQL get diagnostics :exception_count = NUMBER,
:overflow = MORE;
printf("EXCEPTIONS: Number=%d\t", exception_count);
printf("More? %s\n", overflow);
for (i = 1; i <= exception_count; i++)
{
EXEC SQL get diagnostics exception :i
:sqlstate_code = RETURNED_SQLSTATE,
:class_id = CLASS_ORIGIN, :subclass_id = SUBCLASS_ORIGIN,
:message = MESSAGE_TEXT, :messlen = MESSAGE_LENGTH;
printf("- - - - - - - - - - - - - - - - - - - -\n");
printf("EXCEPTION %d: SQLSTATE=%s\n", i,
sqlstate_code);
message[messlen-1] ='\0';
printf("MESSAGE TEXT: %s\n", message);
1-336
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
j = stleng(class_id);
while((class_id[j] == '\0') ||
(class_id[j] == ' '))
j--;
class_id[j+1] = '\0';
printf("CLASS ORIGIN: %s\n",class_id);
j = stleng(subclass_id);
while((subclass_id[j] == '\0') ||
(subclass_id[j] == ' '))
j--;
subclass_id[j+1] = '\0';
printf("SUBCLASS ORIGIN: %s\n",subclass_id);
}
printf("---------------------------------");
printf("-------------------------\n");
}
SQL Statements 1-337
GET DIAGNOSTICS
The following program shows how the GET DIAGNOSTICS statement
retrieves ESQL/COBOL exception information:
*
IDENTIFICATION DIVISION.
PROGRAM-ID.
DIAGCHK.
*
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IFXSUN.
OBJECT-COMPUTER. IFXSUN.
*
DATA DIVISION.
WORKING-STORAGE SECTION.
*
*Declare variables.
*
EXEC SQL BEGIN DECLARE SECTION END-EXEC.
77 EXCEPTION-COUNT PIC S9(9) COMP-5.
77 ROW-COUNT PIC S9(9) COMP-5.
77 MORE-CHAR PIC X(1).
77 COUNT-EX PIC S9(9) VALUE 1 COMP-5.
77 SQLSTATE PIC X(5).
77 CLASS-ORIGIN PIC X(254).
77 SUBCLASS-ORIGIN PIC X(254).
77 ERROR-MESS PIC X(254).
77 MESS-LEN PIC S9(9) COMP-5.
77 SERVER-NAME PIC X(254).
77 CONNECT-NAME PIC X(254).
EXEC SQL END DECLARE SECTION END-EXEC.
*
PROCEDURE DIVISION.
RESIDENT SECTION 1.
*
*Begin Main routine. Execute an SQL statement.
*Determine number of exceptions and pass
*control to ERR-CHK subroutine to diagnose each
*exception.
*
MAIN.
DISPLAY 'START PROGRAM.'.
DISPLAY 'SQLSTATE VALUE IS: ', SQLSTATE.
DISPLAY 'SQLCODE VALUE IS: ', SQLCODE.
DISPLAY '*************************************'.
DISPLAY 'CONNECTING TO DATABASE.'.
DISPLAY '*************************************'.
EXEC SQL CONNECT TO "stores7" END-EXEC.
DISPLAY 'RUNNING DIAGNOSTICS EVALUATION.'.
DISPLAY '*************************************'.
EXEC SQL GET DIAGNOSTICS
:EXCEPTION-COUNT=NUMBER END-EXEC.
DISPLAY 'NUMBER OF EXCEPTIONS IS: ', EXCEPTION-COUNT.
DISPLAY 'NUMBER OF ROWS MODIFIED?: ', ROW-COUNT.
1-338
Informix Guide to SQL: Syntax
GET DIAGNOSTICS
DISPLAY 'MORE EXCEPTIONS DETECTED?: ', MORE-CHAR.
DISPLAY 'PERFORMING ERROR CHECKING.'.
DISPLAY '*************************************'.
PERFORM ERR-CHK UNTIL COUNT-EX IS GREATER THAN
EXCEPTION-COUNT.
DISPLAY '*************************************'.
DISPLAY 'DISCONNECTING FROM DATABASE.'.
DISPLAY '*************************************'.
EXEC SQL DISCONNECT CURRENT END-EXEC.
DISPLAY 'END PROGRAM.'.
STOP RUN.
*
*Subroutine to diagnose each exception generated by the
*execution of an SQL CONNECT TO statement. Display the
*diagnostic information.
*
ERR-CHK.
EXEC SQL GET DIAGNOSTICS EXCEPTION :COUNT-EX
:SQLSTATE=RETURNED_SQLSTATE,
:CLASS-ORIGIN=CLASS_ORIGIN,
:SUBCLASS-ORIGIN=SUBCLASS_ORIGIN,
:ERROR-MESS=MESSAGE_TEXT,
:MESS-LEN=MESSAGE_LENGTH,
:SERVER-NAME=SERVER_NAME,
:CONNECT-NAME=CONNECTION_NAME
END-EXEC.
DISPLAY 'THE SQLSTATE VALUE IS: ', SQLSTATE.
DISPLAY 'THE CLASS CODE ORIGIN IS: ', CLASS-ORIGIN.
DISPLAY 'THE SUBCLASS CODE ORIGIN IS: ', SUBCLASS-ORIGIN.
DISPLAY 'THE ERROR MESSAGE IS: ', ERROR-MESS.
DISPLAY 'THE ERROR MESSAGE LENGTH IS: ', MESS-LEN.
DISPLAY 'THE SERVER NAME IS: ', SERVER-NAME.
DISPLAY 'THE CONNECTION NAME IS: ', CONNECT-NAME.
ADD 1 TO COUNT-EX.
*
SQL Statements 1-339
GRANT
GRANT
Use the GRANT statement to grant privileges on a database, table, view, or
procedure to a user or a role. You can also use GRANT to grant privileges on
a table, view, or procedure to a role. In addition, you can use GRANT to grant
a role to a user or to another role.
Syntax
GRANT
DatabaseLevel
Privileges
p. 1-342
+
TO
PUBLIC
,
user
' user '
OL
+
role name
TO
PUBLIC
,
user
' user '
role
name
' role
name'
+
EXECUTE ON
Procedure
Name
p. 1-754
Table Privileges
for PUBLIC
and Users
p. 1-346
OL
+
1-340
Informix Guide to SQL: Syntax
Table Privileges
for Roles
p. 1-348
WITH
GRANT
OPTION
GRANT
Element
role name
user
Purpose
The name of the role that is
granted, or the name of the role
to which another role is granted
The name of the user to whom a
role is granted, or the name of a
user who receives the specified
privilege
Restrictions
Syntax
The role must have been created Identifier, p. 1-723
with the CREATE ROLE
statement.
If you use quotes around user,
Identifier, p. 1-723
the name of the user is stored
exactly as you typed it. In an
ANSI-compliant database, the
name of the user is stored as
uppercase letters if you do not
use quotes around user. If you
grant a privilege to PUBLIC, you
do not need to grant the
privilege to individual users
because PUBLIC extends the
privilege to all authorized users.
Usage
A GRANT statement can extend user privileges but cannot limit existing
privileges. Later GRANT statements do not affect privileges already granted
to a user. When database-level privileges collide with table-level privileges,
the more-restrictive privileges take precedence. You can grant table-level
privileges on a table or on a view.
Privileges granted to users remain in effect until you cancel them with a
REVOKE statement. Only grantors can revoke the privileges that they
previously issued.
You can grant privileges to a role, and you can grant a role to individual users
or to another role. See “Granting a Role to a User or Another Role” on
page 1-345 for further information.
SE
You cannot use a ROLLBACK WORK statement to undo a GRANT statement
that executes successfully. If you roll back a transaction that contains a
GRANT statement, the privilege is not revoked, and you do not receive an
error message. ♦
SQL Statements 1-341
GRANT
Database-Level Privileges
Database-Level
Privileges
CONNECT
RESOURCE
DBA
When you create a database, you alone have access to it. The database
remains inaccessible to other users until you, as DBA, grant database
privileges.
1-342
Informix Guide to SQL: Syntax
GRANT
Three levels of database privileges control access. These privilege levels are,
from lowest to highest, Connect, Resource, and DBA. These privileges are
associated with the following keywords.
Privilege
Functions
CONNECT
Gives you the ability to query and modify data. You can modify the
database schema if you own the object you want to modify. Any
user with the Connect privilege can perform the following
functions:
RESOURCE
■
Connect to the database with the CONNECT statement or
another connection statement
■
Execute SELECT, INSERT, UPDATE, and DELETE statements, provided the user has the necessary table-level privileges
■
Create views, provided the user has the Select privilege on the
underlying tables
■
Create synonyms
■
Create temporary tables and create indexes on the temporary
tables
■
Alter or drop a table or an index, provided the user owns the
table or index (or has Alter, Index, or References privileges on
the table)
■
Grant privileges on a table or view, provided the user owns the
table (or has been given privileges on the table with the WITH
GRANT OPTION keyword)
Gives you the ability to extend the structure of the database. In
addition to the capabilities of the Connect privilege, the holder of
the Resource privilege can perform the following functions:
■
Create new tables
■
Create new indexes
■
Create new procedures
(1 of 2)
SQL Statements 1-343
GRANT
Privilege
Functions
DBA
Has all the capabilities of the Resource privilege as well as the
ability to perform the following functions:
SE
■
Grant any database-level privilege, including the DBA privilege,
to another user
■
Grant any table-level privilege to another user
■
Grant any table-level privilege to a role
■
Grant a role to a user or to another role
■
Execute the SET SESSION AUTHORIZATION statement
■
Use the NEXT SIZE keyword to alter extent sizes in the system
catalog
■
Insert, delete, or update rows of any system catalog table except
systables
■
Drop any object, regardless of its owner
■
Create tables, views, and indexes, and specify another user as
owner of the objects
■
Execute the DROP DATABASE statement
■
Execute the DROP DISTRIBUTIONS option of the UPDATE
STATISTICS statement
■
Execute the START DATABASE and ROLLFORWARD DATABASE
statements ♦
(2 of 2)
User informix has the privilege required to alter tables in the system catalog,
including the systables table.
Warning: Although the user informix and DBAs can modify most system catalog
tables (only user informix can modify systables), Informix strongly recommends
that you do not update, delete, or alter any rows in them. Modifying the system
catalog tables can destroy the integrity of the database.
The following example uses the PUBLIC keyword to grant the Connect
privilege on the currently active database to all users:
GRANT CONNECT TO PUBLIC
1-344
Informix Guide to SQL: Syntax
GRANT
Granting a Role to a User or Another Role
You can use the GRANT statement to grant a role to another role or user. You
can only grant roles that have been created with the CREATE ROLE statement.
See the CREATE ROLE statement on page 1-145 for an explanation of roles.
After a role is granted, you must use the SET ROLE statement to enable the
role. Users who have been granted a role with the WITH GRANT OPTION can
grant that role to other users or roles. Roles that are granted to users remain
granted until a REVOKE statement cancels them.
Table-level privileges and the Execute privilege to stored procedures can be
granted to roles. Database-level privileges cannot be granted to roles.
The DBA or a user who is granted the role with the WITH GRANT OPTION can
grant a role to a user or to another role. A role cannot be granted to itself,
either directly or indirectly. The following statement causes an error:
GRANT engineer TO engineer -- Causes an error
The following example grants the role engineer to the user maryf:
GRANT engineer TO maryf
The following example grants the role acct to the role engineer:
GRANT acct TO engineer
The following example grants the role engineer with the WITH GRANT
OPTION to the user maryf. This privilege allows maryf to grant the role
engineer to other users or roles.
GRANT engineer TO maryf WITH GRANT OPTION
Stored Procedure Privileges
Use the EXECUTE ON option with a procedure name to grant another user or
a role the ability to run a stored procedure that you own.
When you create an owner-privileged stored procedure, the default privilege
is PUBLIC.
SE
If you create a procedure in a database that is ANSI compliant, no defaultlevel privileges are granted. ♦
SQL Statements 1-345
GRANT
Table Privileges for PUBLIC and Users
Table Privileges for
PUBLIC and Users
TableLevel
Privileges
p. 1-349
ON
Table
Name
p. 1-768
TO
View
Name
p. 1-772
PUBLIC
,
user
' user '
Synonym
Name
p. 1-766
+
+
WITH GRANT OPTION
1-346
Informix Guide to SQL: Syntax
AS grantor
GRANT
Element
grantor
user
Purpose
The name of the person who is to
be listed as the source of the
specified privilege in the
systabauth system catalog table.
The person who issues the
GRANT statement is the default
grantor of the privilege.
The name of the user who
receives the specified privilege
Restrictions
Syntax
If you specify someone else as
Identifier, p. 1-723
the grantor of the specified
privilege to user, you cannot later
revoke that privilege from user.
If you use quotes around user,
Identifier, p. 1-723
the name of the user is stored
exactly as you typed it. In an
ANSI-compliant database, the
name of the user is stored as
uppercase letters if you do not
use quotes around user. If you
grant a privilege to PUBLIC, you
do not need to grant the
privilege to individual users
because PUBLIC extends the
privilege to all authorized users.
Also see “Restricting Privileges
at the Table Level” on
page 1-352.
You can grant privileges on a table, view, or synonym to a user, a list of users,
or all users (PUBLIC). When you grant these privileges to users or PUBLIC,
you can also specify the WITH GRANT OPTION clause and the AS grantor
clause.
The following example grants the table-level privilege Insert on table1 to the
user named mary:
GRANT INSERT ON table1 TO mary
SQL Statements 1-347
GRANT
Table Privileges for Roles
Table Privileges
for Roles
TableLevel
Privileges
p. 1-349
ON
Table
Name
p. 1-768
View
Name
p. 1-772
TO
role name
' role name'
Synonym
Name
p. 1-766
AS grantor
Element
grantor
role name
Purpose
The name of the person who is to
be listed as the source of the
specified privilege in the
systabauth system catalog table.
The person who issues the
GRANT statement is the default
grantor of the privilege.
The name of the role to which
the specified privilege is granted
Restrictions
Syntax
If you specify someone else as
Identifier, p. 1-723
the grantor of the specified
privilege to role name, you cannot
later revoke that privilege from
role name.
The role must have been created Identifier, p. 1-723
with the CREATE ROLE
statement.
You can grant privileges on a table, view, or synonym to a role. When you
grant these privileges to a role, you can also specify the AS grantor clause, but
you cannot specify the WITH GRANT OPTION clause.
The following example grants the table-level privilege Insert on table1 to the
role engineer:
GRANT INSERT ON table1 TO engineer
1-348
Informix Guide to SQL: Syntax
GRANT
Table-Level Privileges
Table-Level Privileges
ALL
PRIVILEGES
,
INSERT
DELETE
SELECT
,
+
(
UPDATE
,
+
(
,
(
INDEX
)
column
name
REFERENCES
+
)
column
name
column
name
)
ALTER
Element
column name
Purpose
Restrictions
The name of the column or
The specified column or
columns to which a Select,
columns must exist.
Update, or References privilege
is restricted. If you omit column
name, the privilege applies to all
columns in the specified table.
Syntax
Identifier, p. 1-723
SQL Statements 1-349
GRANT
As the owner of a table, or as the DBA, you control access to the table through
seven table-level privileges. Four privileges control access to the table data:
Select, Insert, Delete, and Update. The remaining three privileges are Index,
which controls index creation; Alter, which controls the ability to change the
table definition or alter an index; and References, which controls the ability
to place referential constraints on table columns.
The person who creates a table is its owner and receives all seven table-level
privileges. Table ownership cannot be transferred to another user.
To use the GRANT statement, list the privileges that you are granting to user.
If you are granting all table-level privileges, use the keyword ALL. If you are
granting the Select, Update, or References privilege, you can limit the
privileges by listing the names of specific columns.
If you are granting the Alter privilege with the intent of allowing a user to
make changes to a table, you must also grant the Resource privilege for the
database in which the table resides.
If you are granting the Index privilege with the intent of allowing user to
make changes to the underlying structure of a table, be aware that user must
also have the Resource privilege for the database to be able to modify the
database structure. The table-level privileges are defined in the following
table.
Privilege
Functions
INSERT
Provides the ability to insert rows.
DELETE
Provides the ability to delete rows.
SELECT
Provides the ability to name any column in SELECT
statements. You can restrict the Select privilege to one or more
columns by listing them.
UPDATE
Provides the ability to name any column in UPDATE
statements. You can restrict the Update privilege to one or
more columns by listing them.
(1 of 2)
1-350
Informix Guide to SQL: Syntax
GRANT
Privilege
Functions
REFERENCES
Provides the ability to reference columns in referential
constraints. You must have the Resource privilege to take
advantage of the References privilege. (However, you can add
a referential constraint during an ALTER TABLE statement.
This action does not require that you have the Resource
privilege on the database.) You can restrict the References
privilege to one or more columns by listing them.
You need only the References privilege to indicate cascading
deletes. You do not need the Delete privilege to place
cascading deletes on a table.
INDEX
Provides the ability to create permanent indexes. You must
have Resource privilege to use the Index privilege. (Any user
with the Connect privilege can create an index on temporary
tables.)
ALTER
Provides the ability to add or delete columns, modify column
data types, or add or delete constraints. This privilege also
provides the ability to set the object mode of unique indexes
and constraints to the enabled, disabled, or filtering mode. In
addition, this privilege provides the ability to set the object
mode of nonunique indexes and triggers to the enabled or
disabled modes. You must have Resource privilege to use the
Alter privilege.
ALL
Provides all privileges. The PRIVILEGES keyword is optional.
(2 of 2)
The following example grants, to users mary and john, the Delete and Select
privileges on all columns. It also grants the Update privilege on
customer_num, fname, and lname for the customer table.
GRANT DELETE, SELECT, UPDATE (customer_num, fname, lname)
ON customer TO mary, john
To grant these table-level privileges to all authorized users, use the keyword
PUBLIC as shown in the following example:
GRANT DELETE, SELECT, UPDATE (customer_num, fname, lname)
ON customer TO PUBLIC
SQL Statements 1-351
GRANT
Restricting Privileges at the Table Level
You must take action to restrict privileges at the table level. The database
server automatically grants to PUBLIC all table-level privileges, except Alter
and References, when you create a table. To limit table access, you must
revoke all privileges and regrant only those you want, as the following
example shows:
REVOKE ALL ON customer FROM PUBLIC
GRANT ALL ON customer TO john, mary
GRANT SELECT (fname, lname, company, city)
ON customer TO PUBLIC
ANSI
In an ANSI-compliant database, only the table owner receives privileges
when a table is created. ♦
Behavior of the ALL Keyword
The ALL keyword keyword grants all table-level privileges to the specified
user. If any or all of the table-level privileges do not exist for the grantor, the
GRANT statement with the ALL keyword succeeds, but the following
SQLSTATE warning is returned:
01007 - Privilege not granted.
For example, assume that the user ted has the Select and Insert privileges on
the customer table with the authority to grant those privileges to other users.
User ted wants to grant all seven table-level privileges to user tania. So user
ted issues the following GRANT statement:
GRANT ALL ON customer TO tania
This statement executes successfully but returns SQLSTATE code 01007. The
SQLSTATE warning is returned with a successful statement for the following
reasons:
■
The statement succeeds in granting the Select and Insert privileges to
user tania because user ted has those privileges and the right to grant
those privileges to other users.
■
SQLSTATE code 01007 is returned because the other five privileges
implied by the ALL keyword (the Delete, Update, References, Index,
and Alter privileges) were not grantable by user ted and, therefore,
were not granted to user tania.
1-352
Informix Guide to SQL: Syntax
GRANT
WITH GRANT OPTION Keyword
Using the WITH GRANT OPTION keyword conveys the specified privilege to
user along with the right to grant those same privileges to other users. You
create a chain of privileges that begins with you and extends to user as well
as to whomever user conveys the right to grant privileges. If you use the
WITH GRANT OPTION keyword, you can no longer control the dissemination
of privileges.
If you revoke from user the privilege that you granted using the WITH GRANT
OPTION keyword, you sever the chain of privileges. That is, when you revoke
privileges from user, you automatically revoke the privileges of all users who
received privileges from user or from the chain that user created (unless user,
or the users who received privileges from user, were granted the same set of
privileges by someone else). The following examples illustrate this situation.
You, as the owner of the table items, issue the following statements to grant
access to the user mary:
REVOKE ALL ON items FROM PUBLIC
GRANT SELECT, UPDATE ON items TO mary WITH GRANT OPTION
The user mary uses her new privilege to grant users cathy and paul access to
the table.
GRANT SELECT, UPDATE ON items TO cathy
GRANT SELECT ON items TO paul
Later you issue the following statement to cancel access privileges for the
user mary on the items table:
REVOKE SELECT, UPDATE ON items FROM mary
This single statement effectively revokes all privileges on the items table
from the users mary, cathy, and paul.
If you want to create a chain of privileges with another user as the source of
the privilege, use the AS grantor clause.
SQL Statements 1-353
GRANT
AS grantor Clause
The AS grantor clause lets you establish a chain of privileges with another
user as the source of the privileges. This relinquishes your ability to break the
chain of privileges. Even a DBA cannot revoke a privilege unless that DBA
originally granted the privilege. The following example illustrates this
situation. You are the owner of the items table, and you grant all privileges
to the user tom, along with the right to grant all privileges:
REVOKE ALL ON items FROM PUBLIC
GRANT ALL ON items TO tom WITH GRANT OPTION
The following example illustrates a different situation. You also grant Select
and Update privileges to the user jim, but you specify that the grant is made
as the user tom. (The records of the database server show that the user tom is
the grantor of the grant in the systabauth system catalog table, rather than
you.)
GRANT SELECT, UPDATE ON items TO jim AS tom
Later, you decide to revoke privileges on the items table from the user tom,
so you issue the following statement:
REVOKE ALL ON items FROM tom
When you try to revoke privileges from the user jim with a similar statement,
however, the database server returns an error, as the following example
shows:
REVOKE SELECT, UPDATE ON items FROM jim
580: Cannot revoke permission.
You get an error because the database-server record shows the original
grantor as the user tom, and you cannot revoke the privilege. Although you
are the table owner, you cannot revoke a privilege that another user granted.
1-354
Informix Guide to SQL: Syntax
GRANT
Privileges on a View
You must explicitly grant access privileges on the view to users, because no
automatic grant is made to public, as is the case with a newly created table.
When you create a view, if you do not own the underlying tables, you must
have at least the Select privilege on the table or columns. As view creator, the
privileges you have on the underlying table apply to the view built on the
table. You do not receive any other privileges or the ability to grant any other
privileges because you own the view on the table. If the view meets all the
requirements for updating, any Delete, Insert, or Update privileges that you
have on the table also apply to the view.
You can grant (or revoke) privileges on a view only if you are the owner of
the underlying tables or if you received these privileges on the table with the
right to grant them (the WITH GRANT OPTION keyword). You cannot grant
Index, Alter, or References privileges on a view (or the All privilege because
All includes Index, References, and Alter).
For views that reference only tables in the current database, if the owner of a
view loses the Select privilege on any table underlying the view, the view is
dropped.
For detailed information, refer to the CREATE TABLE statement, which also
describes creating views.
References
See the CREATE TABLE, GRANT FRAGMENT, REVOKE, and REVOKE
FRAGMENT statements in this manual.
For information on roles, see the CREATE ROLE, DROP ROLE, and SET ROLE
statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussions of database-level
privileges and table-level privileges in Chapter 4 and the discussion of
privileges and security in Chapter 10.
SQL Statements 1-355
GRANT FRAGMENT
GRANT FRAGMENT
The GRANT FRAGMENT statement enables you to grant Insert, Update, and
Delete privileges on individual fragments of a fragmented table.
Syntax
,
OL
+
GRANT
FRAGMENT
Fragment-Level
Privileges
p. 1-358
ON
tablename
(
dbspace
)
,
TO
user
'user'
Element
dbspace
grantor
WITH GRANT
OPTION
Purpose
The name of the dbspace where
the fragment is stored. Use this
parameter to specify the
fragment or fragments on which
privileges are to be granted.
There is no default value.
The name of the user who is to
be listed as the grantor of the
specified privileges in the
grantor column of the
sysfragauth system catalog
table. The user who issues the
GRANT FRAGMENT statement is
the default grantor of the
privileges.
AS
grantor
Restrictions
Syntax
You must specify at least one
Identifier, p. 1-723
dbspace. The specified dbspaces
must exist.
The user specified in grantor
must be a valid user.
Identifier, p. 1-723
(1 of 2)
1-356
Informix Guide to SQL: Syntax
GRANT FRAGMENT
Element
tablename
user
Purpose
The name of the table that
contains the fragment or
fragments on which privileges
are to be granted. There is no
default value.
The name of the user or users to
whom the specified privileges
are to be granted. There is no
default value.
Restrictions
The specified table must exist
and must be fragmented by
expression.
Syntax
Table Name, p. 1-768
If you put quotes around user,
the name of the user is stored
exactly as you typed it. In an
ANSI-compliant database, the
name of the user is stored as
uppercase letters if you do not
use quotes around user.
Identifier, p. 1-723
(2 of 2)
Usage
The GRANT FRAGMENT statement is similar to the GRANT statement. Both
statements grant privileges to users. The difference between the two statements is that you use GRANT to grant privileges on a table while you use
GRANT FRAGMENT to grant privileges on table fragments.
Use the GRANT FRAGMENT statement to grant the Insert, Update, or Delete
privilege on one or more fragments of a table to one or more users.
The GRANT FRAGMENT statement is valid only for tables that are fragmented
according to an expression-based distribution scheme. For an explanation of
expression-based distribution schemes, see the ALTER FRAGMENT statement
on page 1-22.
SQL Statements 1-357
GRANT FRAGMENT
Fragment-Level Privileges
Fragment-Level
Privileges
ALL
,
INSERT
DELETE
UPDATE
The following table defines each of the fragment-level privileges.
Privilege
Functions
ALL
Grants Insert, Update, and Delete privileges on a table
fragment.
INSERT
Grants Insert privilege on a table fragment. This privilege
gives the user the ability to insert rows in the fragment.
DELETE
Grants Delete privilege on a table fragment. This privilege
gives the user the ability to delete rows in the fragment.
UPDATE
Grants Update privilege on a table fragment. This privilege
gives the user the ability to update rows in the fragment and
to name any column of the table in an UPDATE statement.
Definition of Fragment-Level Authority
When a fragmented table is created in an ANSI-compliant database, the table
owner implicitly receives all table-level privileges on the new table, but no
other users receive privileges.
1-358
Informix Guide to SQL: Syntax
GRANT FRAGMENT
When a fragmented table is created in a database that is not ANSI compliant,
the table owner implicitly receives all table-level privileges on the new table,
and other users (that is, PUBLIC) receive the following default set of privileges on the table: Select, Update, Insert, Delete, and Index. The privileges
granted to PUBLIC are explicitly recorded in the systabauth system catalog
table.
A user who has table privileges on a fragmented table has the privileges
implicitly on all fragments of the table. These privileges are not recorded in
the sysfragauth system catalog table.
Whether or not the database is ANSI compliant, you can use the GRANT
FRAGMENT statement to grant explicit Insert, Update, and Delete privileges
on one or more fragments of a table that is fragmented by expression. The
privileges granted by the GRANT FRAGMENT statement are explicitly
recorded in the sysfragauth system catalog table.
The Insert, Update, and Delete privileges that are conferred on table
fragments by the GRANT FRAGMENT statement are collectively known as
fragment-level privileges or fragment-level authority.
Role of Fragment-Level Authority in Command Validation
Fragment-level authority lets users execute INSERT, DELETE, and UPDATE
statements on table fragments even if they lack Insert, Update, and Delete
privileges on the table as a whole. Users who lack privileges at the table level
can insert, delete, and update rows in authorized fragments because of the
algorithm by which OnLine validates commands. This algorithm consists of
the following checks:
1.
When a user executes an INSERT, DELETE, or UPDATE statement, the
database server first checks whether the user has the table authority
necessary for the operation attempted. If the table authority exists,
the command continues processing.
2.
If the table authority does not exist, the database server checks
whether the table is fragmented by expression. If the table is not fragmented by expression, the database server returns an error to the
user. This error indicates that the user does not have the privilege to
execute the command.
SQL Statements 1-359
GRANT FRAGMENT
3.
If the table is fragmented by expression, the database server checks
whether the user has the fragment authority necessary for the operation attempted. If the fragment authority exists, the command
continues processing. If the fragment authority does not exist, the
database server returns an error to the user. This error indicates that
the user does not have the privilege to execute the command.
Duration of Fragment-Level Authority
The duration of fragment-level authority is tied to the duration of the
fragmentation strategy for the table as a whole.
If you drop a fragmentation strategy by means of a DROP TABLE statement or
the INIT, DROP, or DETACH clauses of an ALTER FRAGMENT statement, you
also drop any authorities that exist for the affected fragments. Similarly, if
you drop a dbspace, you also drop any authorities that exist for the fragment
that resides in that dbspace.
Tables that are created as a result of a DETACH or INIT clause of an ALTER
FRAGMENT statement do not keep the authorities that the former fragment
or fragments had when they were part of the fragmented table. Instead, such
tables assume the default table authorities.
If a table with fragment authorities defined on it is changed to a table with a
round-robin strategy or some other expression strategy, the fragment
authorities are also dropped, and the table assumes the default table
authorities.
Granting Privileges on One Fragment or a List of Fragments
You can grant fragment-level privileges on one fragment of a table or on a list
of fragments.
Granting Privileges on One Fragment
The following statement grants the Insert, Update, and Delete privileges on
the fragment of the customer table in dbsp1 to the user larry:
GRANT FRAGMENT ALL ON customer (dbsp1) TO larry
1-360
Informix Guide to SQL: Syntax
GRANT FRAGMENT
Granting Privileges on More Than One Fragment
The following statement grants the Insert, Update, and Delete privileges on
the fragments of the customer table in dbsp1 and dbsp2 to the user millie:
GRANT FRAGMENT ALL ON customer (dbsp1, dbsp2) TO millie
Granting Privileges on All Fragments of a Table
If you want to grant privileges on all fragments of a table to the same user or
users, you can use the GRANT statement instead of the GRANT FRAGMENT
statement. However, you can also use the GRANT FRAGMENT statement for
this purpose.
Assume that the customer table is fragmented by expression into three
fragments, and these fragments reside in the dbspaces named dbsp1, dbsp2,
and dbsp3. You can use either of the following statements to grant the Insert
privilege on all fragments of the table to the user helen:
GRANT FRAGMENT INSERT ON customer (dbsp1, dbsp2, dbsp3)
TO helen;
GRANT INSERT ON customer TO helen;
Granting Privileges to One User or a List of Users
You can grant fragment-level privileges to a single user or to a list of users.
Granting Privileges to One User
The following statement grants the Insert, Update, and Delete privileges on
the fragment of the customer table in dbsp3 to the user oswald:
GRANT FRAGMENT ALL ON customer (dbsp3) TO oswald
Granting Privileges to a List of Users
The following statement grants the Insert, Update, and Delete privileges on
the fragment of the customer table in dbsp3 to the users jerome and hilda:
GRANT FRAGMENT ALL ON customer (dbsp3) TO jerome, hilda
SQL Statements 1-361
GRANT FRAGMENT
Granting One Privilege or a List of Privileges
When you specify fragment-level privileges in a GRANT FRAGMENT
statement, you can specify one privilege, a list of privileges, or all privileges.
Granting One Privilege
The following statement grants the Update privilege on the fragment of the
customer table in dbsp1 to the user ed:
GRANT FRAGMENT UPDATE ON customer (dbsp1) TO ed
Granting a List of Privileges
The following statement grants the Update and Insert privileges on the
fragment of the customer table in dbsp1 to the user susan:
GRANT FRAGMENT UPDATE, INSERT ON customer (dbsp1) TO susan
Granting All Privileges
The following statement grants the Insert, Update, and Delete privileges on
the fragment of the customer table in dbsp1 to the user harry:
GRANT FRAGMENT ALL ON customer (dbsp1) TO harry
WITH GRANT OPTION Clause
By including the WITH GRANT OPTION clause in the GRANT FRAGMENT
statement, you convey the specified fragment-level privileges to a user and
the right to grant those same privileges to other users.
The following statement grants the Update privilege on the fragment of the
customer table in dbsp3 to the user george and gives this user the right to
grant the Update privilege on the same fragment to other users:
GRANT FRAGMENT UPDATE ON customer (dbsp3) TO george
WITH GRANT OPTION
1-362
Informix Guide to SQL: Syntax
GRANT FRAGMENT
AS grantor Clause
The AS grantor clause is optional in a GRANT FRAGMENT statement. Use this
clause to specify the grantor of the privilege.
Including the AS grantor Clause
When you include the AS grantor clause in the GRANT FRAGMENT statement,
you specify that the user who is named in the grantor parameter is listed as
the grantor of the privilege in the grantor column of the sysfragauth system
catalog table.
In the following example, the DBA grants the Delete privilege on the
fragment of the customer table in dbsp3 to the user martha. In the GRANT
FRAGMENT statement, the DBA uses the AS grantor clause to specify that the
user jack is listed as the grantor of the privilege in the sysfragauth system
catalog table.
GRANT FRAGMENT DELETE ON customer (dbsp3) TO martha AS jack
Omitting the AS grantor Clause
When a GRANT FRAGMENT statement does not include the AS grantor clause,
the user who issues the statement is the default grantor of the privileges that
are specified in the statement.
In the following example, the user grants the Update privilege on the
fragment of the customer table in dbsp3 to the user fred. Because this
statement does not specify the AS grantor clause, the user who issues the
statement is listed by default as the grantor of the privilege in the sysfragauth
system catalog table.
GRANT FRAGMENT UPDATE ON customer (dbsp3) TO fred
SQL Statements 1-363
GRANT FRAGMENT
Consequences of the AS grantor Clause
If you omit the AS grantor clause, or if you specify your own user name in the
grantor parameter, you can later revoke the privilege that you granted to the
specified user. However, if you specify someone other than yourself as the
grantor of the specified privilege to the specified user, only that grantor can
revoke the privilege from the user.
For example, if you grant the Delete privilege on the fragment of the
customer table in dbsp3 to user martha but specify user jack as the grantor
of the privilege, user jack can revoke that privilege from user martha, but you
cannot revoke that privilege from user martha.
References
See the GRANT and REVOKE FRAGMENT statements in this manual.
1-364
Informix Guide to SQL: Syntax
INFO
INFO
Use the INFO statement to display a variety of information about databases
and tables.
Syntax
DB
INFO
TABLES
+
COLUMNS
FOR
Table
Name
p. 1-768
INDEXES
ACCESS
PRIVILEGES
REFERENCES
STATUS
OL
FRAGMENTS
Usage
You can display the following types of information when you issue the INFO
statement:
■
Tables names in the current database
■
Column information for a specified table
■
Index information for a specified table
■
Access privileges for a specified table
■
References privileges for the columns of a specified table
■
Status information for a specified table
■
Fragmentation strategy for a table
SQL Statements 1-365
INFO
Instead of using the INFO statement, you can use the Info options on
the <vk>SQL menu or the TABLE menu to display the same and additional
information.
Displaying Tables, Columns, Indexes, and Fragments
You can use keywords in your INFO statement to display a list of tables,
information about the columns of a table, information about the indexes of a
table, or information about fragments.
TABLES Keyword
Use the TABLES keyword to display a list of the tables in the current database.
The name of a table can appear in one of the following ways:
■
If you are the owner of the cust_calls table, it appears as cust_calls.
■
If you are not the owner of the cust_calls table, the owner’s name
precedes the table name, such as 'june'.cust_calls.
COLUMNS Keyword
Use the COLUMNS keyword to display the names and data types of the
columns in a specified table and whether null values are allowed. The
following examples show an INFO statement and the resulting display of
information about the columns in a table:
INFO statement requesting column information
INFO COLUMNS FOR cust_calls
Display of column information
Column name
customer_num
call_dtime
user_id
call_code
call_descr
res_dtime
res_descr
1-366
Informix Guide to SQL: Syntax
Type
INTEGER
DATETIME YEAR TO MINUTE
CHAR(18)
CHAR(1)
CHAR(240)
DATETIME YEAR TO MINUTE
CHAR(240)
Nulls
no
yes
yes
yes
yes
yes
yes
INFO
INDEXES Keyword
Use the INDEXES keyword to display the name, owner, and type of each
index in a specified table, whether the index is clustered, and the names of
the columns that are indexed. The following examples show an INFO
statement and the resulting display of information about the indexes of a
table:
INFO statement requesting index information
INFO INDEXES FOR cust_calls
Display of index information
Index name
Owner
Type
Cluster
Columns
c_num_dt_ix
velma
unique
No
c_num_cus_ix
velma
dupls
No
customer_num
call_dtime
customer_num
FRAGMENTS Keyword
Use the FRAGMENTS keyword to display the dbspace names where
fragments are located for a specified table. The following examples show an
INFO statement and the resulting display of fragments for a table that is
fragmented with a round-robin distribution scheme. An INFO statement that
is executed on a table that is fragmented with an expression-based distribution scheme would show the expressions and the dbspaces.
INFO statement requesting fragment information
INFO FRAGMENTS FOR new_accts
Display of fragment information
dbsp1
dbsp2
dbsp3
SQL Statements 1-367
INFO
Displaying Privileges, References, and Status
You can use keywords in your INFO statement to display information about
the access privileges (including the References privilege) or the status of a
table.
ACCESS Keyword
Use the ACCESS or PRIVILEGES keywords to display user access privileges for
a specified table. The following examples show an INFO statement and the
resulting display of user privileges for a table:
INFO statement requesting privileges information
INFO PRIVILEGES FOR cust_calls
Display of privileges information
User
Select
Update
Insert
Delete
Index
Alter
All
All
Yes
Yes
Yes
No
public
REFERENCES Keyword
Use the REFERENCES keyword to display the References privilege for users
for the columns of a specified table. The following examples show an INFO
statement and the resulting display:
INFO statement requesting References privilege information
INFO REFERENCES FOR newtable
Display of References privilege information
User
Column References
betty
col1
col2
col3
All
None
wilma
public
The output indicates that the user betty can reference columns col1, col2, and
col3 of the specified table; the user wilma can reference all the columns in the
table; and public cannot access any columns in the table.
1-368
Informix Guide to SQL: Syntax
INFO
If you want information about database-level privileges, you must use a
SELECT statement to access the sysusers system catalog table.
See the GRANT and REVOKE statements for more information about database
and table-access privileges.
STATUS Keyword
Use the STATUS keyword to display information about the owner, row length,
number of rows and columns, creation date, and status of audit trails for a
specified table. The following example displays status information for a table
on an INFORMIX-SE database server:
INFO statement requesting status information
INFO STATUS FOR cust_calls
Display of status information
Table Name
Owner
Row Size
Number of Rows
Number of Columns
Date Created
cust_calls
velma
517
7
7
01/28/1993
The audit-trail file line does not appear for tables in the INFORMIX-OnLine
Dynamic Server databases.
SQL Statements 1-369
INSERT
INSERT
Use the INSERT statement to insert one or more new rows into a table or view.
Syntax
INSERT INTO
Table
Name
p. 1-768
VALUES Clause
p. 1-375
,
View
Name
p. 1-772
(
column
name
Synonym
Name
p. 1-766
)
SELECT
Statement
(Subset)
p. 1-378
+
EXECUTE PROCEDURE
Procedure
Name
p. 1-754
(
,
Argument
Argument
Expression
p. 1-671
parameter
name
1-370
Informix Guide to SQL: Syntax
=
SELECT
Statement
(Singleton)
p. 1-459
)
INSERT
Element
column name
Purpose
The name of a column that
receives a new column value, or
a list of columns that receive
new values. If you specify a
column list, values are inserted
into columns in the order in
which you list the columns. If
you do not specify a column list,
values are inserted into columns
in the column order that was
established when the table was
created or last altered.
parameter name The name of an input parameter
to the procedure
Restrictions
Syntax
The number of columns you
Identifier, p. 1-723
specify must equal the number
of values supplied in the VALUES
clause or by the SELECT
statement, either implicitly or
explicitly. If you omit a column
from the column list, and the
column does not have a default
value associated with it, the
database server places a null
value in the column when the
INSERT statement is executed.
The input parameter must have Expression, p. 1-671
been defined in the CREATE
PROCEDURE statement for the
specified procedure.
Usage
Use the INSERT statement to create either a single new row of column values
or a group of new rows using data selected from other tables.
To insert data into a table, you must either own the table or have the Insert
privilege for the table (see the GRANT statement on page 1-340). To insert data
into a view, you must have the required Insert privilege, and the view must
meet the requirements explained in “Inserting Rows Through a View.”
If you insert data into a table that has data integrity constraints associated
with it, the inserted data must meet the constraint criteria. If it does not, the
database server returns an error.
If you are using effective checking, and the checking mode is set to
IMMEDIATE, all specified constraints are checked at the end of each INSERT
statement. If the checking mode is set to DEFERRED, all specified constraints
are not checked until the transaction is committed.
SQL Statements 1-371
INSERT
Specifying Columns
If you do not explicitly specify one or more columns, data is inserted into
columns using the column order that was established when the table was
created or last altered. The column order is listed in the syscolumns system
catalog table.
ESQL
You can use the DESCRIBE statement with an INSERT statement to determine
the column order and the data type of the columns in a table. (For more information about the DESCRIBE statement, see page 1-255.) ♦
The number of columns specified in the INSERT INTO clause must equal the
number of values supplied in the VALUES clause or by the SELECT statement,
either implicitly or explicitly. If you specify columns, the columns receive
data in the order in which you list them. The first value following the VALUES
keyword is inserted into the first column listed, the second value is inserted
into the second column listed, and so on.
Inserting Rows Through a View
You can insert data through a single-table view if you have the Insert privilege
on the view. To do this, the defining SELECT statement can select from only
one table, and it cannot contain any of the following components:
■
DISTINCT keyword
■
GROUP BY clause
■
Derived value (also referred to as a virtual column)
■
Aggregate value
Columns in the underlying table that are unspecified in the view receive
either a default value or a null value if no default is specified. If one of these
columns does not specify a default value, and a null value is not allowed, the
insert fails.
You can use data-integrity constraints to prevent users from inserting values
into the underlying table that do not fit the view-defining SELECT statement.
For further information, refer to the WITH CHECK OPTION discussion under
the CREATE VIEW statement on page 1-227.
1-372
Informix Guide to SQL: Syntax
INSERT
If several users are entering sensitive information into a single table, the USER
function can limit their view to only the specific rows that each user inserted.
The following example contains a view and an INSERT statement that achieve
this effect:
CREATE VIEW salary_view AS
SELECT lname, fname, current_salary
FROM salary
WHERE entered_by = USER
INSERT INTO salary
VALUES ('Smith', 'Pat', 75000, USER)
Inserting Rows with a Cursor
ESQL
If you associate a cursor with an INSERT statement, you must use the OPEN,
PUT, and CLOSE statements to carry out the INSERT operation. For databases
that have transactions but are not ANSI-compliant, you must issue these
statements within a transaction.
If you are using a cursor that is associated with an INSERT statement, the rows
are buffered before they are written to the disk. The insert buffer is flushed
under the following conditions:
■
The buffer becomes full.
■
A FLUSH statement executes.
■
A CLOSE statement closes the cursor.
■
In a database that is not ANSI-compliant, an OPEN statement
implicitly closes and then reopens the cursor.
■
A COMMIT WORK statement ends the transaction.
When the insert buffer is flushed, the client processor performs appropriate
data conversion before it sends the rows to the database server. When the
database server receives the buffer, it begins to insert the rows one at a time
into the database. If an error is encountered while the database server inserts
the buffered rows into the database, any buffered rows following the last
successfully inserted rows are discarded. ♦
SQL Statements 1-373
INSERT
Inserting Rows into a Database Without Transactions
If you are inserting rows into a database without transactions, you must take
explicit action to restore inserted rows after a failure. For example, if the
INSERT statement fails after inserting some rows, the successfully inserted
rows remain in the table. You cannot recover automatically from a failed
insert.
Inserting Rows into a Database with Transactions
If you are inserting rows into a database with transactions, and you are using
explicit transactions, use the ROLLBACK WORK statement to undo the
insertion. If you do not execute BEGIN WORK before the insert, and the insert
fails, the database server automatically rolls back any database modifications
made since the beginning of the insert.
ANSI
If you are inserting rows into an ANSI-compliant database, transactions are
implicit, and all database modifications take place within a transaction. In
this case, if an INSERT statement fails, use the ROLLBACK WORK statement to
undo the insertions.
If you are using INFORMIX-OnLine Dynamic Server within an explicit transaction, and the update fails, the database server automatically undoes the
effects of the update. ♦
Rows that you insert within a transaction remain locked until the end of the
transaction. The end of a transaction is either a COMMIT WORK statement,
where all modifications are made to the database, or a ROLLBACK WORK
statement, where none of the modifications are made to the database. If many
rows are affected by a single INSERT statement, you can exceed the maximum
number of simultaneous locks permitted. To prevent this situation, either
insert fewer rows per transaction or lock the page, or the entire table, before
you execute the INSERT statement.
SE
1-374
To prevent this situation, either insert fewer rows per transaction, or lock the
entire table before you execute the INSERT statement. ♦
Informix Guide to SQL: Syntax
INSERT
VALUES Clause
VALUES Clause
VALUES
,
ESQL
(
variable
name
)
: indicator variable
+
$ indicator variable
NULL
Literal Number
p. 1-752
Quoted String
p. 1-757
+
USER
p. 1-678
Literal DATETIME
p. 1-746
Literal INTERVAL
p. 1-749
TODAY p. 1-680
CURRENT p. 1-680
OL
SITENAME p. 1-679
DBSERVERNAME
p. 1-679
SQL Statements 1-375
INSERT
Element
indicator
variable
Purpose
A program variable associated
with variable name that indicates
when an <vk>SQL API statement
returns a null value to variable
name
Restrictions
See your SQL API manual for the
restrictions that apply to
indicator variables in a
particular language.
variable name
A host variable that specifies a
value to be inserted into a
column
You can specify in variable name
any other value option listed in
the VALUES clause (NULL,
Literal Number, and so on). If
you specify a quoted string in
variable name, the string can be
longer than the 256-byte
maximum that applies to your
specified quoted strings.
Syntax
The name of the
indicator variable
must conform to
language-specific
rules for naming
indicator variables.
The name of the host
variable must
conform to
language-specific
rules for variable
names.
When you use the VALUES clause, you can insert only one row at a time. Each
value that follows the VALUES keyword is assigned to the corresponding
column listed in the INSERT INTO clause (or in column order if a list of
columns is not specified).
If you are inserting a quoted string into a column, the maximum length of the
string is 256 bytes. If you insert a value greater than 256, the database server
returns an error.
ESQL
If you are using variables, you can insert quoted strings longer than 256 bytes
into a table. ♦
Value and Column Data Type Compatibility
Although the values you insert do not have to be the same data type as the
columns receiving them, the value data type and column data type must be
compatible. You can insert only characters into CHAR columns and only
numbers or characters that represent number data into number columns. The
following example inserts values into the columns of the customer table:
INSERT INTO customer
VALUES (0, 'Nadia', 'Broadam', 'Ski & Stuff',
'89 Coniston Road', NULL, 'Short Hills',
'NJ', '07079', '201-457-4100')
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Informix Guide to SQL: Syntax
INSERT
The database server makes every effort to perform data conversion. If the
data cannot be converted, the INSERT operation fails. Data conversion also
fails if the target data type cannot hold the value that is specified. For
example, you cannot insert the integer 123456 into a column defined as a
SMALLINT data type because this data type cannot hold a number that large.
Inserting Values into SERIAL Columns
If you want to insert consecutive serial values into a SERIAL column in the
table, enter a zero for a SERIAL column in the INSERT statement. When a
SERIAL column is set to zero, the database server assigns the next highest
value. If you want to enter an explicit value into a SERIAL column, specify the
nonzero value after you first verify that the value does not duplicate one
already in the table. If the SERIAL column is uniquely indexed or has a unique
constraint, and you try to insert a value that duplicates one already in the
table, an error occurs. For more information about the SERIAL data type, see
Chapter 3 of the Informix Guide to SQL: Reference.
Using Functions in the VALUES Clause
You can insert the current date, date and time, login name of the current user,
or database server name of the current INFORMIX-OnLine Dynamic Server
database into a column. The TODAY keyword returns the system date. The
CURRENT keyword returns the system date and time. The USER keyword
returns an eight-character string that contains the login account name of the
current user. The SITENAME or DBSERVERNAME keyword returns the
database server name where the current database resides. The following
example uses the CURRENT and USER keywords to insert a new row into the
cust_calls table:
INSERT INTO cust_calls (customer_num, call_dtime, user_id,
call_code, call_descr)
VALUES (212, CURRENT, USER, 'L', '2 days')
SQL Statements 1-377
INSERT
Inserting Nulls with the VALUES Clause
When you execute an INSERT statement, a null value is inserted into any
column for which you do not provide a value as well as for all columns that
do not have default values associated with them, which are not listed
explicitly. You also can use the NULL keyword to indicate that a column
should be assigned a null value. The following example inserts values into
three columns of the orders table:
INSERT INTO orders (orders_num, order_date, customer_num)
VALUES (0, NULL, 123)
In this example, a null value is explicitly entered in the order_date column,
and all other columns of the orders table that are not explicitly listed in the
INSERT INTO clause are also filled with null values.
Subset of SELECT Statement
You can insert the rows of data that result from a SELECT statement into a
table if the insert data is selected from another table or tables. If this statement
has a WHERE clause that does not return rows, sqlca returns SQLNOTFOUND
(100) for ANSI-compliant databases. In databases that are not ANSI
compliant, sqlca returns (0). When you insert as a part of a multistatement
prepare, and no rows are inserted, sqlca returns SQLNOTFOUND (100) for
both ANSI databases and databases that are not ANSI compliant. The
following SELECT clauses are not supported:
■
INTO TEMP
■
ORDER BY
■
UNION
In addition, the FROM clause of the SELECT statement cannot contain the
same table name as the table into which you are inserting rows, as shown in
the following example:
INSERT INTO newtable
SELECT item_num, order_num, quantity, stock_num,
manu_code, total_price
FROM items
For detailed information on SELECT statement syntax, see page 1-459.
1-378
Informix Guide to SQL: Syntax
INSERT
Using INSERT as a Dynamic Management Statement
ESQL
You can use the INSERT statement to handle situations where you need to
write code that can insert data whose structure is unknown at the time you
compile. For more information, refer to the dynamic management section of
your SQL API manual. ♦
Inserting Data Using a Stored Procedure
You can insert the rows of data that result from a procedure call into a table.
The values that the procedure returns must match those expected by the
column list in number and data type. The number and data types of the
columns must match those that the column list expects.
References
See the SELECT statement in this manual. Also see the DECLARE, DESCRIBE,
EXECUTE, FLUSH, OPEN, PREPARE, and PUT statements in this manual for
specific information about dynamic management statements.
In the Informix Guide to SQL: Tutorial, see the discussion of inserting data in
Chapter 4 and Chapter 6. In the Guide to GLS Functionality, see the discussion
of the GLS aspects of the INSERT statement.
SQL Statements 1-379
LOAD
LOAD
Use the LOAD statement to insert data from an operating-system file into an
existing table, synonym, or view.
Syntax
LOAD FROM
'filename'
DELIMITER
INSERT INTO
Table
Name
p. 1-768
Synonym
Name
p. 1-766
View
Name
p. 1-772
1-380
Informix Guide to SQL: Syntax
'delimiter'
,
)
DB
+
column
name
)
LOAD
Element
column name
delimiter
filename
Purpose
The name of a column or
columns that receive data values
from the load file during the
load operation
Restrictions
You must specify the columns
that receive data if you are not
loading data into all columns.
You must also specify columns if
the order of the fields in the load
file does not match the default
order of the columns in the table
(the order established when the
table was created).
A quoted string that identifies
If you do not specify a delimiter
the character to use as the
character, the database server
delimiter in the load file. The
uses the setting in the
DBDELIMITER environment
delimiter is a character that
separates the data values in each variable. If DBDELIMITER has
not been set, the default
line of the load file.
delimiter is the vertical bar (|).
You cannot use the following
items as delimiter characters:
backslash (\), new-line character
(=CTRL-J), and hexadecimal
numbers (0-9, a-f, A-F).
A quoted string that identifies
If you do not include a list of
the pathname and filename of
columns in the column name
the load file. The load file
parameter, the fields in the load
contains the data to be loaded
file must match the columns
into the specified table or view. specified for the table in number,
The default pathname for the
order, and type. You must also
load file is the current directory. observe restrictions about the
same number of fields in each
line, the relationship of field
lengths to column lengths, the
representation of data types in
the file, the use of the backslash
character (\) with certain special
characters, and special rules for
VARCHAR and BLOB data types.
See “The LOAD FROM File” on
page 1-382 for information on
these restrictions.
Syntax
Identifier, p. 1-723
Quoted String,
p. 1-757
Quoted String,
p. 1-757. The
pathname and
filename specified in
the quoted string
must conform to the
conventions of your
operating system.
SQL Statements 1-381
LOAD
Usage
The LOAD statement appends new rows to the table. It does not overwrite
existing data.
You cannot add a row that has the same key as an existing row.
To use the LOAD statement, you must have Insert privileges for the table
where you want to insert data. For information on database-level and tablelevel privileges, see the GRANT statement on page 1-340.
The LOAD FROM File
The LOAD FROM file contains the data to add to a table. You can use the file
that the UNLOAD statement creates as the LOAD FROM file.
If you do not include a list of columns in the INSERT INTO clause, the fields
in the file must match the columns that are specified for the table in number,
order, and data type.
Each line of the file must have the same number of fields. You must define
field lengths that are less than or equal to the length that is specified for the
corresponding column. Specify only values that can convert to the data type
of the corresponding column. The following table indicates how your
Informix product expects you to represent the data types in the LOAD file
(when they use the default locale, U.S. English).
1-382
Informix Guide to SQL: Syntax
LOAD
GLS
Type of Data
Input Format
blank
One or more blank characters between delimiters. You can
include leading blanks in fields that do not correspond to
character columns.
date
A character string in the following format: mm/dd/year. You
must state the month as a two-digit number. You can use a
two-digit number for the year if the year is in the 20th
century. (You can specify another century algorithm with
the DBCENTURY environment variable.) The value must be
an actual date; for example, February 30 is illegal. You can
use a different date format if yo indicate this format with
the GL_DATE or DBDATE environment variable. See
Chapter 2 of the Guide to GLS Functionality for more information about these environment variables.
MONEY
A value that can include currency notation: a leading
currency symbol ($), a comma (,) as the thousands
separator, and a period (.) as the decimal separator. You can
use different currency notation if you indicate this notation
with the DBMONEY environment variable. For more information on this environment variable, see Chapter 2 of the
Guide to GLS Functionality.
NULL
Nothing between the delimiters.
time
A character string in the following format: year-month-day
hour:minute:second.fraction. You cannot use type specification or qualifiers for DATETIME or INTERVAL values. The
year must be a four-digit number, and the month must be
a two-digit number. You can specify a different date and
time format with the GL_DATETIME or DBTIME
environment variable. See Chapter 2 of the Guide to GLS
Functionality for more information on these environment
variables.
If you are using a nondefault locale, the formats of DATE, DATETIME, MONEY,
and numeric column values in the LOAD FROM file must be compatible with
the formats that the locale supports for these data types. For more information, see Chapter 3 of the Guide to GLS Functionality. ♦
SQL Statements 1-383
LOAD
If you include any of the following special characters as part of the value of a
field, you must precede the character with a backslash (\):
■
Backslash
■
Delimiter
■
New-line character anywhere in the value of a VARCHAR or
NVARCHAR column
■
New-line character at end of a value for a TEXT value
Do not use the backslash character (\) as a field separator. It serves as an
escape character to inform the LOAD statement that the next character is to be
interpreted as part of the data.
The fields that correspond to character columns can contain more characters
than the defined maximum allows for the field. The extra characters are
ignored.
If you are loading files that contain VARCHAR or BLOB data types, note the
following information:
■
If you give the LOAD statement data in which the character fields
(including VARCHAR) are longer than the column size, the excess
characters are disregarded.
■
You cannot have leading and trailing blanks in BYTE fields.
■
Use the backslash (\) to escape embedded delimiter and backslash
characters in all character fields, including VARCHAR and TEXT.
■
Data being loaded into a BYTE column must be in ASCII-hexadecimal
form. BYTE columns cannot contain preceding blanks.
■
Do not use the following as delimiting characters in the LOAD FROM
file: 0 to 9, a to f, A to F, backslash, new-line character.
For more information about the format of the input file, see the discussion of
the dbload utility in the Informix Guide to SQL: Reference.
The following example shows the contents of a hypothetical input file named
new_custs:
0|Jeffery|Padgett|Wheel Thrills|3450 El Camino|Suite 10|Palo
Alto|CA|94306||
0|Linda|Lane|Palo Alto Bicycles|2344 University||Palo
Alto|CA|94301|(415)323-6440
1-384
Informix Guide to SQL: Syntax
LOAD
This data file conveys the following information:
■
Indicates a serial field by specifying a zero (0)
■
Uses the vertical bar (|), the default delimiter character
■
Assigns null values to the phone field for the first row and the
address2 field for the second row. The null values are shown by two
delimiter characters with nothing between them.
The following statement loads the values from the new_custs file into the
customer table owned by jason:
LOAD FROM 'new_custs' INSERT INTO jason.customer
DELIMITER Clause
Use the DELIMITER clause to specify the delimiter that separates the data
contained in each column in a row in the input file. If you omit this clause,
your Informix product checks the DBDELIMITER environment variable.
If the DBDELIMITER environment variable has not been set, the default
delimiter is the vertical bar (|). See Chapter 4 in the Informix Guide to SQL:
Reference for information about how to set the DBDELIMITER environment
variable.
You can specify TAB (CTRL-I) or <blank> (= ASCII 32) as the delimiter symbol.
You cannot use the following items as the delimiter symbol:
■
Backslash (\)
■
New-line character (= CTRL-J)
■
Hexadecimal numbers (0 to 9, a to f, A to F)
The following statement identifies the semicolon (;) as the delimiting
character:
LOAD FROM '/a/data/ord.loadfile' DELIMITER ';'
INSERT INTO orders
SQL Statements 1-385
LOAD
INSERT INTO Clause
Use the INSERT INTO clause to specify the table, synonym, or view in which
to load the new data. (See the discussion of Synonym Name, Table Name,
and View Name that begins on page 1-766 for details.)
You must specify the column names only if one of the following conditions is
true:
■
You are not loading data into all columns.
■
The input file does not match the default order of the columns
(determined when the table was created).
The following example identifies the price and discount columns as the only
columns in which to add data:
LOAD FROM '/tmp/prices' DELIMITER ','
INSERT INTO norman.worktab(price,discount)
References
See the UNLOAD and INSERT statements in this manual.
In the Informix Migration Guide, see the task-oriented discussion of the LOAD
statement and other utilities for moving data.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
LOAD statement.
1-386
Informix Guide to SQL: Syntax
LOCK TABLE
LOCK TABLE
Use the LOCK TABLE statement to control access to a table by other processes.
Syntax
+
LOCK TABLE
Table
Name
p. 1-768
IN
SHARE
MODE
EXCLUSIVE
Synonym
Name
p. 1-766
Usage
You can lock a table if you own the table or have the Select privilege on the
table or on a column in the table, either from a direct grant or from a grant to
PUBLIC. The LOCK TABLE statement fails if the table is already locked in
exclusive mode by another process, or if an exclusive lock is attempted while
another user has locked the table in share mode.
The SHARE keyword locks a table in shared mode. Shared mode allows other
processes read access to the table but denies write access. Other processes
cannot update or delete data if a table is locked in shared mode.
The EXCLUSIVE keyword locks a table in exclusive mode. Exclusive mode
denies other processes both read and write access to the table.
Exclusive-mode locking automatically occurs when you execute the ALTER
INDEX, CREATE INDEX, DROP INDEX, RENAME COLUMN, RENAME TABLE,
and ALTER TABLE statements.
SE
The INFORMIX-SE database server does not permit more than one user to lock
a table in shared mode. ♦
SQL Statements 1-387
LOCK TABLE
Databases with Transactions
If your database was created with transactions, the LOCK TABLE statement
succeeds only if it executes within a transaction. You must issue a BEGIN
WORK statement before you can execute a LOCK TABLE statement.
ANSI
Transactions are implicit in an ANSI-compliant database. The LOCK TABLE
statement succeeds whenever the specified table is not already locked by
another process. ♦
The following guidelines apply to the use of the LOCK TABLE statement
within transactions:
■
You cannot lock system catalog tables.
■
You cannot switch between shared and exclusive table locking
within a transaction. For example, once you lock the table in shared
mode, you cannot upgrade the lock mode to exclusive.
■
If you issue a LOCK TABLE statement before you access a row in the
table, no row locks are set for the table. In this way, you can override
row-level locking and avoid exceeding the maximum number of
locks that are defined in the OnLine configuration.
The maximum number of locks that are allowed by the INFORMIX-SE
database server is a characteristic of the particular operating system
on which your database server is running. ♦
SE
■
All row and table locks release automatically after a transaction is
completed. Note that the UNLOCK TABLE statement fails within a
database that uses transactions.
The following example shows how to change the locking mode of a table in
a database that was created with transaction logging:
BEGIN WORK
LOCK TABLE orders IN EXCLUSIVE MODE
...
COMMIT WORK
BEGIN WORK
LOCK TABLE orders IN SHARE MODE
...
COMMIT WORK
1-388
Informix Guide to SQL: Syntax
LOCK TABLE
Databases Without Transactions
In a database that was created without transactions, table locks set by using
the LOCK TABLE statement are released after any of the following
occurrences:
■
An UNLOCK TABLE statement executes.
■
The user closes the database.
■
The user exits the application.
To change the lock mode on a table, release the lock with the UNLOCK TABLE
statement and then issue a new LOCK TABLE statement.
The following example shows how to change the lock mode of a table in a
database that was created without transactions:
LOCK TABLE orders IN EXCLUSIVE MODE
.
.
.
UNLOCK TABLE orders
.
.
.
LOCK TABLE orders IN SHARE MODE
References
See the BEGIN WORK, SET ISOLATION, SET LOCK MODE, COMMIT WORK,
ROLLBACK WORK, and UNLOCK TABLE statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of locks in Chapter 7.
SQL Statements 1-389
OPEN
OPEN
Use the OPEN statement to activate a cursor associated with a SELECT,
INSERT, or EXECUTE PROCEDURE statement, and thereby begin execution of
the SELECT, INSERT, or EXECUTE PROCEDURE statement.
Syntax
ESQL
OPEN
cursor
id
E/C
+
cursor
variable
WITH REOPTIMIZATION
,
variable name
USING
SQL DESCRIPTOR
'descriptor'
descriptor
variable
E/C
DESCRIPTOR
sqlda
pointer
Element
cursor id
Purpose
It identifies a cursor
Restrictions
Cursor must have been previously created by a DECLARE
statement.
Host variable must be a
character data type. Cursor must
have been previously created by
a DECLARE statement.
cursor variable
Host variable that identifies a
cursor
descriptor
Quoted string that identifies the System-descriptor area must
system-descriptor area
already be allocated.
Syntax
Identifier, p. 1-723
Variable name must
conform to
language-specific
rules for variable
names
Quoted String,
p. 1-757
(1 of 2)
1-390
Informix Guide to SQL: Syntax
OPEN
Element
descriptor
variable
sqlda pointer
variable name
Purpose
Host variable name that
identifies the system-descriptor
area
It points to an sqlda structure
that defines the type and
memory location of values that
correspond to the question-mark
( ?) placeholder in a prepared
statement
Host variable whose contents
replace a question-mark ( ?)
placeholder in a prepared
statement
Restrictions
System-descriptor area must
already be allocated.
Syntax
Quoted String,
p. 1-757
You cannot begin an sqlda pointer DESCRIBE, p. 1-255
with a dollar sign ($) or a colon
(:). You must use an sqlda
structure if you are using
dynamic SQL statements.
Variable must be a character
data type.
Variable name must
conform to
language-specific
rules for variable
names.
(2 of 2)
Usage
You create a cursor with a statement that uses the DECLARE statement (see
page 1-234). When the program opens the cursor, the associated SELECT,
INSERT, or EXECUTE PROCEDURE statement is passed to the database server,
which begins execution. When the program has retrieved or inserted all the
rows it needs, close the cursor by using the CLOSE statement.
The specific actions that the database server takes differ, depending on
whether the cursor is associated with a SELECT statement or an INSERT
statement.
The SELECT, INSERT, or EXECUTE PROCEDURE statement associated with a
cursor is prepared implicitly by the OPEN statement. The total number of
prepared objects and open cursors that are allowed in one program at any
time is limited by the available memory. You can use the FREE statement to
free the cursor and release the database server resources.
ANSI
You receive an error code if you try to open a cursor that is already open. ♦
SQL Statements 1-391
OPEN
Opening a Select Cursor
When you open either a select cursor or an update cursor, the SELECT
statement is passed to the database server along with any values that are
specified in the USING clause. (If the statement was previously prepared, the
statement passed to the database server when it was prepared.) The database
server processes the query to the point of locating or constructing the first
row of the active set.
Because the database server is seeing the query for the first time, many errors
are detected. The database server does not actually return the first row of
data, but it sets a return code in the SQLCODE field of the sqlca. The name of
the field in each <vk>SQL API product is indicated in the following table.
Product
Field Name
ESQL/C
sqlca.sqlcode, SQLCODE
ESQL/COBOL
SQLCODE OF SQLCA
The return code value is either negative or zero, as the following table
describes.
Return Code Value
Meaning
Negative
Shows an error is detected in the SELECT statement.
Zero
Shows the SELECT statement is valid.
If the SELECT statement is valid, but no rows match its criteria, the first
FETCH statement returns a value of 100 (SQLNOTFOUND), which means no
rows were found.
Tip: When you encounter an SQLCODE error, a corresponding SQLSTATE error
value might exist. Check the GET DIAGNOSTICS statement for information about
how to get the SQLSTATE value and how to use the GET DIAGNOSTICS statement
to interpret the SQLSTATE value.
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Informix Guide to SQL: Syntax
OPEN
The following example illustrates a simple OPEN statement in
INFORMIX-ESQL/C:
EXEC SQL declare s_curs cursor for
select * from orders;
EXEC SQL open s_curs;
If you are working in a database with explicit transactions, you must open an
update cursor within a transaction. This requirement is waived if you
declared the cursor using the WITH HOLD keyword. (See the DECLARE
statement on page 1-234.)
Opening a Procedure Cursor
When you open a procedure cursor, the EXECUTE PROCEDURE statement is
passed to the database server along with any values that are specified in the
USING clause. The values are passed as arguments to the stored procedure,
and the procedure must be declared to accept values. (If the statement was
previously prepared, the statement passed to the database server when it was
prepared.) The database server executes the procedure to the point of the first
set of values returned by the procedure.
Because the database server is seeing the procedure for the first time, many
errors are detected. The database server does not actually return the first row
of data, but it sets a return code in the SQLCODE field of the sqlca. The name
of the field in each product is indicated in the following table.
Product
Field Name
ESQL/C
sqlca.sqlcode, SQLCODE
ESQL/COBOL
SQLCODE OF SQLCA
SQL Statements 1-393
OPEN
The return-code value is either negative or zero, as described in the following
table.
Return Code Value
Negative
Meaning
Shows that an error was detected in the EXECUTE
PROCEDURE statement.
Zero
Shows that the EXECUTE PROCEDURE statement is valid.
If the EXECUTE PROCEDURE statement is valid, but no rows are returned, the
first FETCH statement returns a value of 100 (SQLNOTFOUND), which means
no rows found. The procedure must be created to return values; that is, the
procedure must have a RETURNING clause at the beginning of the procedure.
Tip: When you encounter an SQLCODE error, be aware that there may be a
corresponding SQLSTATE error value. Check the GET DIAGNOSTICS statement for
information about how to get the SQLSTATE value and how to use the GET
DIAGNOSTICS statement to interpret the SQLSTATE value.
The following example illustrates a simple OPEN statement in
INFORMIX-ESQL/C:
EXEC SQL declare s_curs cursor for
execute procedure new_proc();
EXEC SQL open s_curs;
Opening an Insert Cursor
When you open an insert cursor, the cursor passes the INSERT statement to
the database server, which checks the validity of the keywords and column
names. The database server also allocates memory for an insert buffer to hold
new data. (See the DECLARE statement on page 1-234.)
An OPEN statement for a cursor that is associated with an INSERT statement
cannot include a USING clause.
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Informix Guide to SQL: Syntax
OPEN
The following INFORMIX-ESQL/C example illustrates an OPEN statement
with an insert cursor:
EXEC SQL prepare s1 from
'insert into manufact values ('npr', 'napier')';
EXEC SQL declare in_curs cursor for s1;
EXEC SQL open in_curs;
EXEC SQL put in_curs;
EXEC SQL close in_curs;
Reopening a Select Cursor
The values that are named in the USING clause are evaluated only when the
cursor is opened. While the cursor is open, subsequent changes to program
variables in the USING clause do not change the active set of selected rows.
The active set remains constant until a subsequent OPEN statement closes the
cursor and reopens it or until the program closes the open cursor, which
releases the active set.
Reopening the cursor creates a new active set that is based on the current
values of the variables. If the program variables have changed since the
previous OPEN statement, reopening the cursor can generate an entirely
different active set. Even if the values of the variables are unchanged, if data
in the table was modified since the previous OPEN statement, the rows in the
active set can be different.
Reopening a Procedure Cursor
The values that are named in the USING clause are evaluated only when the
cursor is opened. While the cursor is open, subsequent changes to program
variables in the USING clause do not change the active set of returned rows.
The active set remains constant until a subsequent OPEN statement closes the
cursor and reopens it or until the program closes the open cursor, which
releases the active set.
Reopening the cursor creates a new active set that is based on the current
values of the variables. If the program variables have changed since the
previous OPEN statement, reopening the cursor can generate an entirely
different active set. Even if the values of the variables are unchanged, if the
procedure takes a different execution path from the previous OPEN
statement, the rows in the active set can be different.
SQL Statements 1-395
OPEN
Reopening an Insert Cursor
When you reopen an insert cursor that is already open, you effectively flush
the insert buffer; any rows that are stored in the insert buffer are written into
the database table. The database server first closes the cursor, which causes
the flush and then reopens the cursor. See the discussion of the PUT statement
on page 1-416 for information about checking errors and counting inserted
rows.
USING Clause
The USING clause is required when the cursor is associated with a prepared
SELECT statement that includes question-mark (?) placeholders. (See the
PREPARE statement on page 1-402.) You can supply values for these parameters in one of two ways. You can specify host variables in the USING clause,
or you can specify a system-descriptor area in the USING SQL DESCRIPTOR
clause.
Naming Variables in USING
If you know the number of parameters to be supplied at runtime and their
data types, you can define the parameters that are needed by the statement
as host variables in your program. You pass parameters to the database
server by opening the cursor with the USING keyword, followed by the
names of the variables. These variables are matched with the SELECT
statement question-mark (?) parameters in a one-to-one correspondence,
from left to right.
You cannot include indicator variables in the list of variable names. To use an
indicator variable, you must include the SELECT statement as part of the
DECLARE statement.
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Informix Guide to SQL: Syntax
OPEN
The following example illustrates the USING clause with the OPEN statement
in an INFORMIX-ESQL/C code fragment:
sprintf (select_1, "%s %s %s %s %s",
"SELECT o.order_num, sum(total price)",
"FROM orders o, items i",
"WHERE o.order_date > ? AND o.customer_num = ?",
"AND o.order_num = i.order_num",
"GROUP BY o.order_num");
EXEC SQL prepare statement_1 from :select_1;
EXEC SQL declare q_curs cursor for statement_1;
EXEC SQL open q_curs using :o_date, :o_total;
USING SQL DESCRIPTOR Clause
You can also associate input values from a system-descriptor area. The
keywords USING SQL DESCRIPTOR indicate the use of a system descriptor.
This allows you to associate input values from a system-descriptor area and
open a cursor.
If a system-descriptor area is used, the count value specifies the number of
input values that are described in occurrences of sqlvar. This number must
correspond to the number of dynamic parameters in the prepared statement.
The value of count must be less than or equal to the value of occurrences that
were specified when the system-descriptor area was allocated.
For further information, refer to the discussion of the system-descriptor area
in the manual for your SQL API. The following examples show the OPEN ...
USING SQL DESCRIPTOR clause:
INFORMIX-ESQL⁄C
EXEC SQL open selcurs using sql descriptor 'desc1';
INFORMIX-ESQL⁄COBOL
EXEC SQL OPEN SEL_CURS USING SQL DESCRIPTOR 'DESC1' END-EXEC.
SQL Statements 1-397
OPEN
USING DESCRIPTOR Clause
E/C
You can pass parameters for a prepared statement in the form of an sqlda
pointer structure, which lists the data type and memory location of one or
more values to replace question-mark (?) placeholders. For further information, refer to the sqlda discussion in the INFORMIX-ESQL/C Programmer’s
Manual. The following example shows the OPEN ... USING DESCRIPTOR
clause in INFORMIX-ESQL/C:
struct sqlda *sdp;
.
.
.
EXEC SQL open selcurs using descriptor sdp;
♦
WITH REOPTIMIZATION Clause
The WITH REOPTIMIZATION clause allows you to reoptimize your querydesign plan. When you prepare a SELECT statement or an EXECUTE
PROCEDURE statement, your Informix database server uses a query-design
plan to optimize that query. If you later modify the data that is associated
with a prepared SELECT statement or the data that is associated with an
EXECUTE PROCEDURE statement, you can compromise the effectiveness of
the query-design plan for that statement. In other words, if you change the
data, you can deoptimize your query. To ensure optimization of your query,
you can prepare the SELECT or EXECUTE PROCEDURE statement again or
open the cursor again using the WITH REOPTIMIZATION clause. Informix
recommends that you use the WITH REOPTIMIZATION clause because it
provides the following advantages over preparing a statement again:
■
Rebuilds only the query-design plan rather than the entire statement
■
Uses fewer resources
■
Reduces overhead
■
Requires less time
The WITH REOPTIMIZATION clause also makes your database server
optimize your query-design plan before processing the OPEN cursor
statement.
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Informix Guide to SQL: Syntax
OPEN
The following example shows the WITH REOPTIMIZATION clause in
INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL, respectively:
INFORMIX-ESQL⁄C
EXEC SQL open selcurs using descriptor sdp with reoptimization;
INFORMIX-ESQL⁄COBOL
EXEC SQL OPEN SEL_CURS USING SQL DESCRIPTOR ‘DESC1’ WITH REOPTIMIZATION END-EXEC.
The Relationship Between OPEN and FREE
The database server allocates resources to prepared statements and open
cursors. If you release resources with a FREE cursor id or FREE cursor variable
statement, you cannot use the cursor unless you declare the cursor again. If
you execute a FREE statement id or FREE statement id variable statement, you
cannot open the cursor that is associated with the statement id or statement
id variable unless you prepare the statement id or statement id variable
again.
References
See the CLOSE, DECLARE, and FREE statements in this manual for cursorrelated information. See the PUT and FLUSH statements in this manual for
information about insert cursors.
See the ALLOCATE DESCRIPTOR, DEALLOCATE DESCRIPTOR, DESCRIBE,
EXECUTE, FETCH, GET DESCRIPTOR, PREPARE, PUT, and SET DESCRIPTOR
statements in this manual for more information about dynamic <vk>SQL
statements.
In the Informix Guide to SQL: Tutorial, see the discussion of the OPEN
statement in Chapter 5. Refer also to your SQL API manual for more information about the system-descriptor area and the sqlda structure.
SQL Statements 1-399
OUTPUT
OUTPUT
Use the OUTPUT statement to send query results directly to an operatingsystem file or to pipe it to another program.
Syntax
DB
+
OUTPUT TO
filename
PIPE program
Element
filename
program
Purpose
The pathname and filename of
an operating-system file where
the results of the query are
written. The default pathname is
the current directory.
The name of a program where
the results of the query are sent
WITHOUT
HEADINGS
Restrictions
You can specify a new or existing
file in filename. If the specified
file exists, the results of the
query overwrite the current
contents of the file.
The program must exist and
must be known to the operating
system. The program must be
able to read the results of a
query.
SELECT
Statement
p. 1-459
Syntax
The pathname and
filename must
conform to the
conventions of your
operating system.
The name of the
program must
conform to the
conventions of your
operating system.
Usage
You can send the results of a query to an operating-system file by specifying
the full pathname for the file. If the file already exists, the output overwrites
the current contents, as the following example shows:
OUTPUT TO /usr/april/query1
SELECT * FROM cust_calls WHERE call_code = 'L'
1-400
Informix Guide to SQL: Syntax
OUTPUT
You can display the results of a query without column headings by using the
WITHOUT HEADINGS keywords, as the following example shows:
OUTPUT TO /usr/april/query1
WITHOUT HEADINGS
SELECT * FROM cust_calls WHERE call_code = 'L'
You also can use the keyword PIPE to send the query results to another
program, as the following example shows:
OUTPUT TO PIPE more
SELECT customer_num, call_dtime, call_code
FROM cust_calls
References
See the SELECT and UNLOAD statements in this manual.
SQL Statements 1-401
PREPARE
PREPARE
Use the PREPARE statement to parse, validate, and generate an execution
plan for SQL statements in an SQL API program at runtime.
Syntax
ESQL
+
PREPARE
statement
id
statement
id variable
Element
statement id
Purpose
The statement identifier
identifies an SQL statement.
statement id
variable
Host variable that contains the
statement identifier
statement
variable name
Host variable whose value is a
character string that consists of
one or more SQL statements
1-402
Informix Guide to SQL: Syntax
FROM
Quoted
String
p. 1-757
statement
variable
name
Restrictions
Syntax
After you release the databaseIdentifier, p. 1-723
server resources (using a FREE
statement), you cannot use the
statement identifier with a
DECLARE cursor or with the
EXECUTE statement until you
prepare the statement again.
This variable must be a character Variable name must
data type.
conform to
language-specific
rules for variable
names.
This variable must be a character Variable name must
data type. For restrictions on the conform to
statements in the character
language-specific
string, see “SQL Statements
rules for variable
Permitted in Single-Statement
names.
Prepares” on page 1-407 and
“Restrictions for Multistatement
Prepares” on page 1-414.
PREPARE
Usage
The PREPARE statement permits your program to assemble the text of an SQL
statement at runtime and make it executable. This dynamic form of SQL is
accomplished in three steps:
1.
A PREPARE statement accepts statement text as input, either as a
quoted string or stored within a character variable. Statement text
can contain question-mark ( ?) placeholders to represent values that
are to be defined when the statement is executed.
2.
An EXECUTE or OPEN statement can supply the required input
values and execute the prepared statement once or many times.
3.
Resources allocated to the prepared statement can be released later
using the FREE statement.
The number of prepared objects in a single program is limited by the
available memory. This includes both statement identifiers that are named in
PREPARE statements (statement id or statement id variable) and cursor declarations that incorporate SELECT, EXECUTE PROCEDURE, or INSERT statements.
To avoid exceeding the limit, use a FREE statement to release some statements
or cursors.
Using a Statement Identifier
A PREPARE statement sends the statement text to the database server where
it is analyzed. If it contains no syntax errors, the text converts to an internal
form. This translated statement is saved for later execution in a data structure
that the PREPARE statement allocates. The name of the structure is the value
that is assigned to the statement identifier in the PREPARE statement. Subsequent SQL statements refer to the structure by using the same statement
identifier that was used in the PREPARE statement.
A subsequent FREE statement releases the resources that were allocated to the
statement. After you release the database-server resources, you cannot use
the statement identifier with a DECLARE cursor or with the EXECUTE
statement until you prepare the statement again.
A program can consist of one or more source-code files. By default, the scope
of a statement identifier is global to the program. Therefore, a statement
identifier that is prepared in one file can be referenced from another file.
SQL Statements 1-403
PREPARE
In a multiple-file program, if you want to limit the scope of a statement
identifier to the file in which it is prepared, preprocess all the files with the
-local command-line option. See the manual for your SQL API for more information, restrictions, and performance issues when preprocessing with the
-local option.
Releasing a Statement Identifier
A statement identifier can represent only one SQL statement or sequence of
statements at a time. You can execute a new PREPARE statement with an
existing statement identifier if you wish to bind a given statement identifier
to a different SQL statement text.
The PREPARE statement supports dynamic statement-identifier names,
which allow you to prepare a statement identifier as an identifier or as a host
character-string variable. In the following ESQL/C and ESQL/COBOL
examples, the first example in each pair shows a statement identifier that was
prepared as an SQL API variable; the second example in each pair shows a
statement identifier that was prepared as a character-string constant:
INFORMIX-ESQL/C
stcopy ("query2", stmtid);
EXEC SQL prepare :stmtid from
'select * from customer';
EXEC SQL prepare query2 from
'select * from customer';
INFORMIX-ESQL/COBOL
MOVE 'QUERY_2' TO STMTID.
EXEC SQL
PREPARE :STMTID FROM
'SELECT * FROM CUSTOMER'
END-EXEC.
EXEC SQL
PREPARE QUERY_2 FROM
'SELECT * FROM CUSTOMER'
END-EXEC.
A statement ID variable must be the CHARACTER data type. In C, it must be
defined as char. In COBOL, ID variables must be declared as a standard
CHARACTER type.
1-404
Informix Guide to SQL: Syntax
PREPARE
Statement Text
The PREPARE statement can take statement text either as a quoted string or as
text that is stored in a program variable. The following restrictions apply to
the statement text:
■
The text can contain only SQL statements. It cannot contain
statements or comments from the host programming language.
■
The text can contain comments that are preceded by a double
dash (--) or enclosed in curly brackets ({ }). These comment symbols
represent SQL comments. For more information on SQL comment
symbols, see “How to Enter SQL Comments” on page 1-9.
■
The text can contain either a single SQL statement or a sequence of
statements that are separated by semicolons. For more information
on preparing a single SQL statement, see “SQL Statements Permitted
in Single-Statement Prepares” on page 1-407. For more information
on preparing a sequence of SQL statements, see “Preparing
Sequences of Multiple SQL Statements” on page 1-412.
■
Names of host-language variables are not recognized as such in
prepared text. Therefore, you cannot prepare a SELECT statement
that contains an INTO clause or an EXECUTE PROCEDURE that
contains an INTO clause because the INTO clause requires a hostlanguage variable.
■
The only identifiers that you can use are names that are defined in the
database, such as names of tables and columns. For further information on using identifiers in statement text, see “Preparing Statements with SQL Identifiers” on page 1-409.
■
Use a question mark (?) as a placeholder to indicate where data is
supplied when the statement executes. For further information on
using question marks as placeholders, see “Preparing Statements
That Receive Parameters” on page 1-408.
■
The text cannot include an embedded SQL statement prefix or
terminator, such as a dollar sign ($) or the words EXEC SQL.
The following example shows a PREPARE statement in INFORMIX-ESQL/C:
EXEC SQL prepare new_cust from
'insert into customer(fname,lname) values(?,?)';
SQL Statements 1-405
PREPARE
Executing Stored Procedures Within a PREPARE Statement
You can prepare an EXECUTE PROCEDURE statement as long as it does not
contain an INTO clause. The way to execute a prepared stored procedure
depends on whether the stored procedure returns values:
■
If the stored procedure does not return values (the procedure does
not contain the RETURN statement), use the EXECUTE statement to
execute the EXECUTE PROCEDURE statement.
■
If the stored procedure returns only one row, you can use the INTO
clause of the EXECUTE statement to specify host variables to hold the
return values. Using EXECUTE ... INTO to execute a stored procedure
that returns more than one row generates a runtime error.
■
If the stored procedure returns more than one row, you must
associate the prepared EXECUTE PROCEDURE statement with a
cursor using the DECLARE statement. You execute the statement with
the OPEN statement and retrieve return values into host variables
using the INTO clause of the FETCH statement.
If you do not know the number and data types of the values that a stored
procedure returns, you must use a dynamic management structure to hold
the returned values. In an ESQL/C or ESQL/COBOL program, you can use
SQL statements such as ALLOCATE DESCRIPTOR and GET DESCRIPTOR to
manage a system-descriptor area. In an ESQL/C program, you can use an
sqlda structure instead of a system-descriptor area. However, a systemdescriptor area conforms to the X/Open standards.
See Chapter 12 of the Informix Guide to SQL: Tutorial for information about
creating and executing stored procedures. See the INFORMIX-ESQL/COBOL
Programmer’s Manual and the INFORMIX-ESQL/C Programmer’s Manual for
detailed information about using dynamic management structures to
dynamically execute a stored procedure.
1-406
Informix Guide to SQL: Syntax
PREPARE
SQL Statements Permitted in Single-Statement Prepares
You can prepare any single SQL statement except the ones in the following
list.
ALLOCATE DESCRIPTOR
GET DIAGNOSTICS
CHECK TABLE
INFO
CLOSE
DEALLOCATE DESCRIPTOR
LOAD
OPEN
DECLARE
OUTPUT
DESCRIBE
EXECUTE IMMEDIATE
PREPARE
PUT
EXECUTE
REPAIR TABLE
FETCH
SET DESCRIPTOR
FLUSH
FREE
UNLOAD
WHENEVER
GET DESCRIPTOR
You can prepare a SELECT statement. If the SELECT statement includes the
INTO TEMP clause, you can execute the prepared statement with an EXECUTE
statement. If it does not include the INTO TEMP clause, the statement returns
rows of data. Use DECLARE, OPEN, and FETCH cursor statements to retrieve
the rows.
A prepared SELECT statement can include a FOR UPDATE clause. This clause
is normally used with the DECLARE statement to create an update cursor. The
following example shows a SELECT statement with a FOR UPDATE clause in
INFORMIX-ESQL/C:
sprintf(up_query, "%s %s %s",
"select * from customer ",
"where customer_num between ? and ? ",
"for update");
EXEC SQL prepare up_sel from :up_query;
EXEC SQL declare up_curs cursor for up_sel;
EXEC SQL open up_curs using :low_cust,:high_cust;
SQL Statements 1-407
PREPARE
Preparing Statements When Parameters Are Known
In some prepared statements, all needed information is known at the time the
statement is prepared. The following example in INFORMIX-ESQL/C shows
two statements that were prepared from constant data:
sprintf(redo_st, "%s %s",
"drop table workt1; ",
"create table workt1 (wtk serial, wtv float)" );
EXEC SQL prepare redotab from :redo_st;
Preparing Statements That Receive Parameters
In some statements, parameters are unknown when the statement is
prepared because a different value can be inserted each time the statement is
executed. In these statements, you can use a question-mark (?) placeholder
where a parameter must be supplied when the statement is executed.
The PREPARE statements in the following INFORMIX-ESQL/C examples show
some uses of question-mark (?) placeholders:
EXEC SQL prepare s3 from
'select * from customer where state matches ?';
EXEC SQL prepare in1 from
'insert into manufact values (?,?,?)';
sprintf(up_query, "%s %s",
"update customer set zipcode = ?"
"where current of zip_cursor");
EXEC SQL prepare update2 from :up_query;
You can use a placeholder to defer evaluation of a value until runtime only
for an expression. You cannot use a question-mark (?) placeholder to
represent an SQL identifier except as noted in “Preparing Statements with
SQL Identifiers” on page 1-409.
1-408
Informix Guide to SQL: Syntax
PREPARE
The following example of an INFORMIX-ESQL/C code fragment prepares a
statement from a variable that is named demoquery. The text in the variable
includes one question-mark (?) placeholder. The prepared statement is
associated with a cursor and, when the cursor is opened, the USING clause of
the OPEN statement supplies a value for the placeholder.
EXEC SQL
char
char
EXEC SQL
BEGIN DECLARE SECTION;
queryvalue [6];
demoquery [80];
END DECLARE SECTION;
EXEC SQL connect to 'stores7';
sprintf(demoquery, "%s %s",
"select fname, lname from customer ",
"where lname > ? ");
EXEC SQL prepare quid from :demoquery;
EXEC SQL declare democursor cursor for quid;
stcopy("C", queryvalue);
EXEC SQL open democursor using :queryvalue;
The USING clause is available in both OPEN (for statements that are
associated with a cursor) and EXECUTE (all other prepared statements)
statements.
Preparing Statements with SQL Identifiers
In general, you cannot use question-mark (?) placeholders for SQL identifiers. You must specify these identifiers in the statement text when you
prepare the statement.
However, in a few special cases, you can use the question mark (?) placeholder for an SQL identifier. These cases are as follows:
E/C
■
You can use the ? placeholder for the database name in the
DATABASE statement.
■
You can use the ? placeholder for the dbspace name in the IN dbspace
clause of the CREATE DATABASE statement
■
You can use the ? placeholder for the cursor name in statements that
use cursor names. ♦
SQL Statements 1-409
PREPARE
Obtaining SQL Identifiers from User Input
If a prepared statement requires identifiers, but the identifiers are unknown
when you write the prepared statement, you can construct a statement that
receives SQL identifiers from user input.
The following INFORMIX-ESQL/C example prompts the user for the name of
a table and uses that name in a SELECT statement. Because the table name is
unknown until runtime, the number and data types of the table columns are
also unknown. Therefore, the program cannot allocate host variables to
receive data from each row in advance. Instead, this program fragment
describes the statement into an sqlda descriptor and fetches each row using
the descriptor. The fetch puts each row into memory locations that the
program provides dynamically.
If a program retrieves all the rows in the active set, the FETCH statement
would be placed in a loop that fetched each row. If the FETCH statement
retrieves more than one data value (column), another loop exists after the
FETCH, which performs some action on each data value.
#include <stdio.h>
EXEC SQL include sqlda;
EXEC SQL include sqltypes;
char *malloc( );
main()
{
struct sqlda *demodesc;
char tablename[19];
int i;
EXEC SQL BEGIN DECLARE SECTION;
char demoselect[200];
EXEC SQL END DECLARE SECTION;
/*
This program selects all the columns of a given tablename.
The tablename is supplied interactively. */
EXEC SQL connect to 'stores7';
printf( "This program does a select * on a table\n" );
printf( "Enter table name: " );
scanf( "%s", tablename );
sprintf(demoselect, "select * from %s", tablename );
EXEC SQL prepare iid from :demoselect;
EXEC SQL describe iid into demodesc;
/* Print what describe returns */
for ( i = 0; i < demodesc->sqld; i++ )
prsqlda (demodesc->sqlvar + i);
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Informix Guide to SQL: Syntax
PREPARE
/* Assign the data pointers. */
for ( i = 0; i < demodesc->sqld; i++ )
{
switch (demodesc->sqlvar[i].sqltype & SQLTYPE)
{
case SQLCHAR:
demodesc->sqlvar[i].sqltype = CCHARTYPE;
demodesc->sqlvar[i].sqllen++;
demodesc->sqlvar[i].sqldata =
malloc( demodesc->sqlvar[i].sqllen );
break;
case SQLSMINT:
/* fall through */
case SQLINT:
/* fall through */
case SQLSERIAL:
demodesc->sqlvar[i].sqltype = CINTTYPE;
demodesc->sqlvar[i].sqldata =
malloc( sizeof( int ) );
break;
/*
And so on for each type.
*/
}
}
/* Declare and open cursor for select . */
EXEC SQL declare d_curs cursor for iid;
EXEC SQL open d_curs;
/* Fetch selected rows one at a time into demodesc. */
for( ; ; )
{
printf( "\n" );
EXEC SQL fetch d_curs using descriptor demodesc;
if ( sqlca.sqlcode != 0 )
break;
for ( i = 0; i < demodesc->sqld; i++ )
{
switch (demodesc->sqlvar[i].sqltype)
{
case CCHARTYPE:
printf( "%s: \"%s\n", demodesc->sqlvar[i].sqlname,
demodesc->sqlvar[i].sqldata );
break;
case CINTTYPE:
printf( "%s: %d\n", demodesc->sqlvar[i].sqlname,
*((int *) demodesc->sqlvar[i].sqldata) );
break;
/* And so forth for each type... */
}
}
}
EXEC SQL close d_curs;
EXEC SQL free d_curs;
SQL Statements 1-411
PREPARE
/*
Free the data memory.
*/
for ( i = 0; i < demodesc->sqld; i++ )
free( demodesc->sqlvar[i].sqldata );
printf ("Program Over.\n");
}
prsqlda(sp)
struct sqlvar_struct *sp;
{
printf ("type = %d\n", sp->sqltype);
printf ("len = %d\n", sp->sqllen);
printf ("data = %lx\n", sp->sqldata);
printf ("ind = %lx\n", sp->sqlind);
printf ("name = %s\n", sp->sqlname);
}
For an explanation of how to use an sqlda structure for statement values, see
the INFORMIX-ESQL/C Programmer’s Manual.
Preparing Sequences of Multiple SQL Statements
You can execute several SQL statements as one action if you include them in
the same PREPARE statement. Multistatement text is processed as a unit;
actions are not treated sequentially. Therefore, multistatement text cannot
include statements that depend on actions that occur in a previous statement
in the text. For example, you cannot create a table and insert values into that
table in the same prepared block.
In most situations, compiled products return error-status information on the
first error in the multistatement text. No indication exists of which statement
in the sequence causes an error. You can use sqlca to find the offset of the
following errors:
■
In ESQL/C: sqlca.sqlerrd[4]
■
In ESQL/COBOL: SQLERRD[5] OF SQLCA
For more information about sqlca and error-status information, see your SQL
API manual.
1-412
Informix Guide to SQL: Syntax
PREPARE
In a multistatement prepare, if no rows are returned from a WHERE clause in
the following statements, you get SQLNOTFOUND (100) in both ANSIcompliant databases and databases that are not ANSI compliant:
■
UPDATE ... WHERE ...
■
SELECT INTO TEMP ... WHERE ...
■
INSERT INTO ... WHERE ...
■
DELETE FROM ...WHERE ...
In the following example, four SQL statements are prepared into a single
INFORMIX-ESQL/C string that is called query. Individual statements are
delimited with semicolons. A single PREPARE statement can prepare the four
statements for execution, and a single EXECUTE statement can execute the
statements that are associated with the qid statement identifier.
sprintf (query, "%s %s %s %s %s %s %s ",
"update account set balance = balance + ? ",
"where acct_number = ?;",
"update teller set balance = balance + ? ",
"where teller_number = ?;",
"update branch set balance = balance + ? ",
"where branch_number = ?;",
"insert into history values (?, ?);";
EXEC SQL prepare qid from :query;
EXEC SQL begin work;
EXEC SQL execute qid using
:delta, :acct_number, :delta, :teller_number,
:delta, :branch_number, :timestamp, :values;
EXEC SQL commit work;
In the preceding code fragment, the semicolons (;) are required as SQL
statement-terminator symbols between each SQL statement in the text that
query holds.
SQL Statements 1-413
PREPARE
printf("Enter customer number (or 0 to quit): ");
scanf("%d", cust_num);
if (cust_num == 0)
break;
EXEC SQL execute up1 using :cust_num;
}
}
References
See the DECLARE, DESCRIBE, EXECUTE, FREE, and OPEN statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of the PREPARE
statement and dynamic SQL in Chapter 5.
SQL Statements 1-415
PUT
PUT
Use the PUT statement to store a row in an insert buffer for later insertion into
the database.
Syntax
ESQL
+
PUT
cursor
id
,
cursor
variable
FROM
variable
name
+
: indicator
variable
$ indicator
variable
INDICATOR
USING
indicator
variable
SQL DESCRIPTOR
descriptor
variable
E/C
DESCRIPTOR
Element
cursor id
Purpose
It identifies a cursor
cursor variable
Host variable that identifies a
cursor
'descriptor'
Restrictions
A DECLARE statement must
have previously created the
cursor.
Host variable must be a
character data type. A DECLARE
statement must have previously
created the cursor.
sqlda
pointer
Syntax
Identifier, p. 1-723
Variable name must
conform to
language-specific
rules for variable
names.
(1 of 2)
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Informix Guide to SQL: Syntax
PUT
Element
descriptor
descriptor
variable
indicator
variable
sqlda pointer
variable name
Purpose
Quoted string that identifies the
system-descriptor area
Host variable name that
identifies the system-descriptor
area
Host variable that receives a
return code if null data is placed
in the corresponding data
variable
Restrictions
System-descriptor area must
already be allocated.
System-descriptor area must
already be allocated.
Syntax
Quoted String,
p. 1-757
Quoted String,
p. 1-757
Variable cannot be a DATETIME
or INTERVAL data type.
Variable name must
conform to
language-specific
rules for variable
names.
It points to an sqlda structure
You cannot begin an sqlda
Prepared statement
that defines the type and
pointer with a dollar sign ($) or a information stored in
memory location of values that colon (:).
sqlda structure by a
DESCRIBE statement,
correspond to the question-mark
p. 1-255.
( ?) placeholder in a prepared
statement
Host variable whose contents
Variable must be a character data Variable name must
replace a question-mark ( ?)
type.
conform to
placeholder in a prepared
language-specific
statement
rules for variable
names.
(2 of 2)
Usage
Each PUT statement stores a row in an insert buffer that was created when
cursor name was opened. If the buffer has no room for the new row when the
statement executes, the buffered rows are written to the database in a block
and the buffer is emptied. As a result, some PUT statement executions cause
rows to be written to the database, and some do not.
You can use the FLUSH statement to write buffered rows to the database
without adding a new row. The CLOSE statement writes any remaining rows
before it closes an insert cursor.
If the current database uses explicit transactions, you must execute a PUT
statement within a transaction.
SQL Statements 1-417
PUT
The following example uses a PUT statement in INFORMIX-ESQL/C:
EXEC SQL prepare ins_mcode from
'insert into manufact values(?,?)';
EXEC SQL declare mcode cursor for ins_mcode;
EXEC SQL open mcode;
EXEC SQL put mcode from :the_code, :the_name;
X/O
PUT is not an X/Open SQL statement. Therefore, you get a warning message
if you compile a PUT statement in X/Open mode in an SQL API product. For
details on compiling in X/Open mode, see your SQL API product manual.♦
Supplying Inserted Values
The values that reside in the inserted row can come from one of the following
sources:
■
Constant values that are written into the INSERT statement
■
Program variables that are named in the INSERT statement
■
Program variables that are named in the FROM clause of the PUT
statement
■
Values that are prepared in memory addressed by an sqlda structure
or a system-descriptor area and then named in the USING clause of
the PUT statement
Using Constant Values in INSERT
The VALUES clause of the INSERT statement lists the values of the inserted
columns. One or more of these values might be constants (that is, numbers or
character strings).
When all the inserted values are constants, the PUT statement has a special
effect. Instead of creating a row and putting it in the buffer, the PUT statement
merely increments a counter. When you use a FLUSH or CLOSE statement to
empty the buffer, one row and a repetition count are sent to the database
server, which inserts that number of rows.
1-418
Informix Guide to SQL: Syntax
PUT
In the following INFORMIX-ESQL/C example, 99 empty customer records are
inserted into the customer table. Because all values are constants, no disk
output occurs until the cursor closes. (The constant zero for customer_num
causes generation of a SERIAL value.)
int count;
EXEC SQL declare fill_c cursor for
insert into customer(customer_num) values(0);
EXEC SQL open fill_c;
for (count = 1; count <= 99; ++count)
EXEC SQL put fill_c;
EXEC SQL close fill_c;
Naming Program Variables in INSERT
When the INSERT statement is written as part of the cursor declaration (in the
DECLARE statement), you can name program variables in the VALUES clause.
When each PUT statement is executed, the contents of the program variables
at that time are used to populate the row that is inserted into the buffer.
If you are creating an insert cursor (using DECLARE with INSERT), you must
use only program variables in the VALUES clause. Variable names are not
recognized in the context of a prepared statement; you associate a prepared
statement with a cursor through its statement identifier.
The following INFORMIX-ESQL/C example illustrates the use of an insert
cursor. The code includes the following statements:
■
The DECLARE statement associates a cursor called ins_curs with an
INSERT statement that inserts data into the customer table. The
VALUES clause names a data structure that is called cust_rec; the
ESQL/C preprocessor converts cust_rec to a list of values, one for
each component of the structure.
■
The OPEN statement creates a buffer.
■
A function that is not defined in the example obtains customer information from an interactive user and leaves it in cust_rec.
■
The PUT statement composes a row from the current contents of the
cust_rec structure and sends it to the row buffer.
SQL Statements 1-419
PUT
■
The CLOSE statement inserts into the customer table any rows that
remain in the row buffer and closes the insert cursor.
int keep_going = 1;
EXEC SQL BEGIN DECLARE SECTION
struct cust_row { /* fields of a row of customer table */ } cust_rec;
EXEC SQL END DECLARE SECTION
EXEC SQL declare ins_curs cursor for
insert into customer values (:cust_row);
EXEC SQL open ins_curs;
for (; (sqlca.sqlcode == 0) && (keep_going) ;)
{
keep_going = get_user_input(cust_rec); /* ask user for new customer */
if (keep_going )
/* user did supply customer info */
{
/* request new serial value */
cust_rec.customer_num = 0;
EXEC SQL put ins_curs;
}
/* no error from PUT */
if (sqlca.sqlcode == 0)
keep_going = (prompt_for_y_or_n("another new customer") =='Y')
}
EXEC SQL close ins_curs;
Naming Program Variables in PUT
When the INSERT statement is prepared (see the PREPARE statement on page
1-402), you cannot use program variables in its VALUES clause. However, you
can represent values using a question-mark (?) placeholder. List the names of
program variables in the FROM clause of the PUT statement to supply the
missing values. The following INFORMIX-ESQL/C example lists host
variables in a PUT statement:
char answer [1] = 'y';
EXEC SQL BEGIN DECLARE SECTION;
char ins_comp[80];
char u_company[20];
EXEC SQL END DECLARE SECTION;
main()
{
EXEC SQL connect to 'stores7';
EXEC SQL prepare ins_comp from
'insert into customer (customer_num, company) values (0, ?)';
EXEC SQL declare ins_curs cursor for ins_comp;
EXEC SQL open ins_curs;
while (1)
{
printf("\nEnter a customer: ");
gets(u_company);
EXEC SQL put ins_curs from :u_company;
printf("Enter another customer (y/n) ? ");
1-420
Informix Guide to SQL: Syntax
PUT
if (answer = getch() != 'y')
break;
}
EXEC SQL close ins_curs;
EXEC SQL disconnect all;
}
Using a System-Descriptor Area
You can create a system-descriptor area that describes the data type and
memory location of one or more values. You can then specify that systemdescriptor area in the USING SQL DESCRIPTOR clause of the PUT statement.
For details on using descriptors, see your SQL API manual. The following
INFORMIX-ESQL/C and INFORMIX-ESQL/COBOL examples show how to
associate values from a system-descriptor area:
INFORMIX-ESQL/C
EXEC SQL put selcurs using sql descriptor 'desc1';
INFORMIX-ESQL/COBOL
EXEC SQL PUT SEL_CURS USING SQL DESCRIPTOR 'DESC1' END-EXEC.
Using an sqlda Structure
E/C
You can create an sqlda structure that describes the data type and memory
location of one or more values. Then you can specify the sqlda structure in
the USING DESCRIPTOR clause of the PUT statement. Each time the PUT
statement executes, the values that the sqlda structure describes are used to
replace question-mark (?) placeholders in the INSERT statement. This process
is similar to using a FROM clause with a list of variables, except that your
program has full control over the memory location of the data values.
The following example shows the usage of the PUT ... USING DESCRIPTOR
clause. For details on the sqlda structure, see the INFORMIX-ESQL/C
Programmer’s Manual.
EXEC SQL put selcurs using descriptor pointer2;
♦
SQL Statements 1-421
PUT
Writing Buffered Rows
When the OPEN statement opens an insert cursor, an insert buffer is created.
The PUT statement puts a row into this insert buffer. The block of buffered
rows is inserted into the database table as a block only when necessary; this
process is called flushing the buffer. The buffer is flushed after any of the
following events:
■
The buffer is too full to hold the new row at the start of a PUT
statement.
■
A FLUSH statement executes.
■
A CLOSE statement closes the cursor.
■
An OPEN statement executes, naming the cursor.
When the OPEN statement is applied to an open cursor, it closes the
cursor before reopening it; this implied CLOSE statement flushes the
buffer.
■
A COMMIT WORK statement executes.
■
The buffer contains blob data (flushed after a single PUT statement).
If the program terminates without closing an insert cursor, the buffer remains
unflushed. Rows that were inserted into the buffer since the last flush are lost.
Do not rely on the end of the program to close the cursor and flush the buffer.
Error Checking
The sqlca contains information on the success of each PUT statement as well
as information that lets you count the rows that were inserted. The result of
each PUT statement is contained in the fields of the sqlca, as the following
table shows.
1-422
ESQL/C
ESQL/COBOL
sqlca.sqlcode, SQLCODE
SQLCODE OF SQLCA
sqlca.sqlerrd[2]
SQLERRD[3] OF SQLCA
Informix Guide to SQL: Syntax
PUT
Data buffering with an insert cursor means that errors are not discovered
until the buffer is flushed. For example, an input value that is incompatible
with the data type of the column for which it is intended is discovered only
when the buffer is flushed. When an error is discovered, rows in the buffer
that are located after the error are not inserted; they are lost from memory.
The SQLCODE field is set to 0 if no error occurs; otherwise, it is set to an error
code. The third element of the sqlerrd array is set to the number of rows that
are successfully inserted into the database:
■
If a row is put into the insert buffer, and buffered rows are not written
to the database, SQLCODE and sqlerrd are set to 0 (SQLCODE because
no error occurred, and sqlerrd because no rows were inserted).
■
If a block of buffered rows is written to the database during the
execution of a PUT statement, SQLCODE is set to 0 and sqlerrd is set
to the number of rows that was successfully inserted into the
database.
■
If an error occurs while the buffered rows are written to the database,
SQLCODE indicates the error, and sqlerrd contains the number of
successfully inserted rows. (The uninserted rows are discarded from
the buffer.)
Tip: When you encounter an SQLCODE error, a corresponding SQLSTATE error
value might exist. Check the GET DIAGNOSTICS statement for information about
how to get the SQLSTATE value and how to use the GET DIAGNOSTICS statement to
interpret the SQLSTATE value.
Counting Total and Pending Rows
To count the number of rows that were actually inserted in the database and
the number not yet inserted, perform the following procedure:
■
Prepare two integer variables (for example, total and pending).
■
When the cursor is opened, set both variables to 0.
■
Each time a PUT statement executes, increment both total and
pending.
■
Whenever a PUT or FLUSH statement executes, or the cursor closes,
subtract the third field of the SQLERRD array from pending.
SQL Statements 1-423
PUT
At any time, (total - pending) represents the number of rows that were
actually inserted. If all commands are successful, pending contains zero after
the cursor is closed. If an error occurs during a PUT, FLUSH, or CLOSE
statement, the value that remains in pending is the number of uninserted
(discarded) rows.
References
See the CLOSE, FLUSH, DECLARE, and OPEN statements, which are cursorrelated, in this manual. Also see the ALLOCATE DESCRIPTOR statement.
In the Informix Guide to SQL: Tutorial, see the discussion of the PUT statement
in Chapter 6.
1-424
Informix Guide to SQL: Syntax
RECOVER TABLE
RECOVER TABLE
Use the RECOVER TABLE statement with INFORMIX-SE to restore a database
table in the event of failure.
Syntax
SE
+
RECOVER TABLE
Table
Name
p. 1-768
Usage
The RECOVER TABLE statement applies the table audit trail to a backup copy
of the database. INFORMIX-SE uses audit trails to record operations on a pertable basis. You can issue a RECOVER TABLE statement if you own the table
or have the DBA privilege for the database.
If a system failure occurs, use an operating-system utility to restore each table
file for which you have an audit trail. Issue the RECOVER TABLE statement to
update each newly restored table with the transactions that are recorded in
the audit trail.
SQL Statements 1-425
RECOVER TABLE
Backup/Restore Procedure
The recommended backup/restore procedure for making backup copies of a
database that includes audit trails is described in the following list:
■
Execute the DROP AUDIT statement for each table that has an audit
trail. The DROP AUDIT statement ends system logging to the audittrail files.
■
Execute the CREATE AUDIT statement for each table, specifying the
pathname of the new audit trail. For maximum protection, specify a
location that is not on the same storage device as the database. You
can also select a filename that reflects the table name and the
sequence of the file in the audit trail (for example, audit_cust_001 or
audit_cust_002). The CREATE AUDIT statement registers the new
name and location of the audit-trail file in the systables system
catalog table.
■
Use an operating-system utility to back up the database files.
During execution, the RECOVER TABLE statement checks that the audit trail
and table name have consistent record numbers for rows where changes
occurred. In extremely rare instances, the RECOVER TABLE statement can find
an inconsistency that a system crash caused. In this case only, the RECOVER
TABLE statement stops, and you must restore the table manually.
The following list of actions and statements serves as a guide to recover the
customer table. First, restore the customer table from your last archive copy.
Second, run the following statements, which assume that your audit trail
began immediately after you created the archive copy:
RECOVER TABLE customer
DROP AUDIT FOR customer
CREATE AUDIT FOR customer
Third, create a new backup of the recovered table.
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Informix Guide to SQL: Syntax
RECOVER TABLE
The audit-trail file is not in human-readable form. Even so, the DBA can copy
the file to a database (.dat) file and manipulate it. The modified file can be
copied back to the audit-trail file, enabling customized restorations of
particular tables. For example, you can modify the audit-trail file to exclude
rows that a particular user entered or to undo specific transactions. For
specific instructions on modifying audit-trail files, refer to the manual for
your application-development tool.
References
See the CREATE AUDIT and DROP AUDIT statements in this manual.
SQL Statements 1-427
RENAME COLUMN
RENAME COLUMN
Use the RENAME COLUMN statement to change the name of a column.
Syntax
+
RENAME COLUMN
Element
new column
name
.old column
name
Table
Name
p. 1-768
.old column name
TO
new column name
Purpose
Restrictions
Syntax
The new name to be assigned to The new name of the column
Identifier, p. 1-723
the column
must be unique within the table.
If you rename a column that
appears within a trigger
definition, the new column
name replaces the old column
name in the trigger definition
only if certain conditions are
met. See “How Triggers Are
Affected” on page 1-429 for
more information on this
restriction.
The current name of the column The column must exist within
Identifier, p. 1-723
you want to rename
the table. The column name
must be preceded by a period.
You can put a space between the
table name and .old column name,
or you can omit the space.
Usage
You can rename a column of a table if any of the following conditions are true:
1-428
■
You own the table.
■
You have the DBA privilege on the database.
■
You have the Alter privilege on the table.
Informix Guide to SQL: Syntax
RENAME COLUMN
When you rename a column, choose a column name that is unique within the
table.
SE
You cannot use a ROLLBACK WORK statement to undo a RENAME COLUMN
statement that successfully executes. If you roll back a transaction that
contains a RENAME COLUMN statement, the column retains its new name,
and you do not receive an error message. ♦
How Views and Check Constraints Are Affected
If you rename a column that a view in the database references, the text of the
view in the sysviews system catalog table is updated to reflect the new
column name.
If you rename a column that a check constraint in the database references, the
text of the check constraint in the syschecks system catalog table is updated
to reflect the new column name.
How Triggers Are Affected
If you rename a column that appears within a trigger, it is replaced with the
new name only in the following instances:
■
When it appears as part of a correlation name inside the FOR EACH
ROW action clause of a trigger
■
When it appears as part of a correlation name in the INTO clause of
an EXECUTE PROCEDURE statement
■
When it appears as a triggering column in the UPDATE clause
When the trigger executes, if the database server encounters a column name
that no longer exists in the table, it returns an error
SQL Statements 1-429
RENAME COLUMN
Example of RENAME COLUMN
The following example assigns the new name of c_num to the
customer_num column in the customer table:
RENAME COLUMN customer.customer_num TO c_num
References
See the ALTER TABLE, CREATE TABLE, and RENAME TABLE statements in this
manual.
1-430
Informix Guide to SQL: Syntax
RENAME DATABASE
RENAME DATABASE
Use the RENAME DATABASE statement to change the name of a database.
Syntax
OL
RENAME DATABASE
old database name
TO
new database name
+
Element
new database
name
old database
name
Purpose
Restrictions
The new name that you want to Name must be unique. You canassign to the database
not rename the current database.
The database to be renamed
must not be opened by any users
when the RENAME DATABASE
command is issued.
The name of the database that
The database name must exist.
you want to rename
Syntax
Database Name,
p. 1-660
Database Name,
p. 1-660
Usage
You can rename a database if either of the following statements is true:
■
You created the database.
■
You have the DBA privilege on the database.
You can only rename local databases. You can rename a local database from
inside a stored procedure.
References
See the CREATE DATABASE statement in this manual.
SQL Statements 1-431
RENAME TABLE
RENAME TABLE
Use the RENAME TABLE statement to change the name of a table.
Syntax
+
Element
new table name
RENAME TABLE
Table
Name
p. 1-768
TO
new table
name
Purpose
Restrictions
The new name that you want to You cannot use the owner.
assign to the table
convention in the new name of
the table.
Syntax
Identifier, p. 1-723
Usage
You can rename a table if any of the following statements are true:
■
You own the table.
■
You have the DBA privilege on the database.
■
You have the Alter privilege on the table.
You cannot change the table owner by renaming the table. You can use the
owner. convention in the old name of the table, but an error occurs during
compilation if you try to use the owner. convention in the new name of the
table.
ANSI
In an ANSI-compliant database, you must use the owner. convention in the old
name of the table if you are referring to a table that you do not own. ♦
You cannot use the RENAME TABLE statement to move a table from the
current database to another database or to move a table from another
database to the current database. The table that you want to rename must
reside in the current database. The renamed table that results from the
statement remains in the current database.
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Informix Guide to SQL: Syntax
RENAME TABLE
SE
You cannot use a ROLLBACK WORK statement to undo a RENAME TABLE
statement that successfully executes. If you roll back a transaction that
contains a RENAME TABLE statement, the table retains its new name, and you
do not receive an error message. ♦
Renaming Tables That Views Reference
If a view references the table that was renamed, and the view resides in the
same database as the table, the database server updates the text of the view
in the sysviews system catalog table to reflect the new table name. See the
Informix Guide to SQL: Reference for further information on the sysviews
system catalog table.
Renaming Tables That Have Triggers
If you rename a table that has a trigger, it produces the following results:
■
The database server replaces the name of the table in the trigger definition.
■
The table name is not replaced where it appears inside any triggered
actions.
■
The database server returns an error if the new table name is the
same as a correlation name in the REFERENCING clause of the trigger
definition.
When the trigger executes, the database server returns an error if it
encounters a table name for which no table exists.
Example of Renaming a Table
The following example reorganizes the items table. The intent is to move the
quantity column from the fifth position to the third. The example illustrates
the following steps:
1.
Create a new table, new_table, that contains the column quantity in
the third position.
2.
Fill the table with data from the current items table.
3.
Drop the old items table.
4.
Rename new_table with the name items.
SQL Statements 1-433
RENAME TABLE
The following example uses the RENAME TABLE statement as the last step:
CREATE TABLE new_table
(
item_num
SMALLINT,
order_num
INTEGER,
quantity
SMALLINT,
stock_num
SMALLINT,
manu_code
CHAR(3),
total_price MONEY(8)
)
INSERT INTO new_table
SELECT item_num, order_num, quantity, stock_num,
manu_code, total_price
FROM items
DROP TABLE items
RENAME TABLE new_table TO items
References
See the ALTER TABLE, CREATE TABLE, DROP TABLE, and RENAME COLUMN
statements in this manual.
1-434
Informix Guide to SQL: Syntax
REPAIR TABLE
REPAIR TABLE
Use the REPAIR TABLE statement to remove and rebuild table indexes or data
that might have been damaged or corrupted because of a power failure,
computer crash, or other unexpected program stoppage. Only damaged
tables are rebuilt. To determine whether you need to use the REPAIR TABLE
statement, you can first issue the CHECK TABLE statement.
Syntax
SE
DB
+
REPAIR TABLE
Table
Name
p. 1-768
Usage
Specify the name of the table for which you want to restore the integrity of
the index files, as the following example shows:
REPAIR TABLE cust_calls
You must specify a table that is in a database in the current directory. If you
specify a simple name for a database in the DATABASE command, but the
database is not located in the current directory, REPAIR TABLE does not search
the DBPATH environment variable to find the directory for the database; the
REPAIR TABLE statement will fail. Similarly, if you specify an explicit
pathname for a database in the DATABASE command, but the database is not
located in the current directory, REPAIR TABLE does not search for the
database in the specified directory; the REPAIR TABLE statement will fail.
You cannot use the REPAIR TABLE statement on a table unless you own it or
have the DBA privilege on the database. You cannot use the REPAIR TABLE
statement on the system catalog table systables unless you have the DBA
privilege on the database.
The REPAIR TABLE statement calls the secheck utility.
SQL Statements 1-435
REPAIR TABLE
References
See the CHECK TABLE statement in this manual.
See the INFORMIX-SE Administrator’s Guide for a full description of secheck.
1-436
Informix Guide to SQL: Syntax
REVOKE
REVOKE
You can use the REVOKE statement for the following purposes:
■
You can revoke privileges on a table or view from a user or a role.
■
You can revoke the privilege to execute a procedure from a user or a
role.
■
You can revoke privileges on a database from a user.
■
You can revoke a role from a user or from another role.
SQL Statements 1-437
REVOKE
Syntax
+
REVOKE
Table-Level
Privileges
p. 1-442
ON
table name
FROM
PUBLIC
,
view name
user
synonym
name
'user '
EXECUTE ON
OL
Procedure
Name
p. 1-754
OL
role
name
role name
' role '
name
Table-Level
Privileges
p. 1-442
ON
table name
FROM
PUBLIC
,
view name
user
synonym
name
'user '
OL
CASCADE
RESTRICT
DatabaseLevel
Privileges
p. 1-445
FROM
PUBLIC
,
user
'user '
1-438
Informix Guide to SQL: Syntax
REVOKE
Element
role name
synonym name
table name
user
view name
Purpose
Names the role from which a
privilege or another role is to be
revoked or names the role to be
revoked from a user or another
role.
The synonym name for which a
privilege is revoked
The table name for which a privilege is revoked
Names the user from whom a
privilege or role is revoked
The view name for which a privilege is revoked
Restriction
Syntax
The role must have been created Identifier, p. 1-723
with the CREATE ROLE statement
and granted with the GRANT
statement
The name must be an existing
synonym name.
The name must be an existing
table name.
The user must be a valid user.
Synonym Name,
p. 1-766
Table Name, p. 1-768
The name must be an existing
view name.
View Name, p. 1-772
Identifier, p. 1-723
Usage
You can use the REVOKE statement with the GRANT statement to control
finely the ability of users to modify the database as well as to access and
modify data in the tables.
If you use the PUBLIC keyword after the FROM keyword, the REVOKE
statement revokes privileges from all users.
You can revoke all or some of the privileges that you granted to other users.
No one can revoke privileges that another user grants.
If you revoke the EXECUTE privilege on a stored procedure from a user, that
user can no longer run that procedure using either the EXECUTE PROCEDURE
or CALL statements.
If you use quotes, user appears exactly as typed.
ANSI
In an ANSI-compliant database, if you do not use quotes around user, the
name of the user is stored in uppercase letters. ♦
Users cannot revoke privileges from themselves.
SQL Statements 1-439
REVOKE
Using the REVOKE Statement with Roles
You can use the REVOKE statement to remove privileges from a role and
remove a role from a user or another role. Once a role is revoked from a user,
the user cannot enable that role. You can revoke all or some of the roles
granted to a user or role.
If a role is revoked from a user, the privileges associated with the role cannot
be acquired by the user with the SET ROLE statement. However, this does not
affect the currently acquired privileges.
You can use the REVOKE statement to revoke table-level privileges from a
role; however, you cannot use the RESTRICT or CASCADE clauses when you
do so.
Only the DBA or a user granted a role with the WITH GRANT OPTION can
revoke privileges for a role.
If you revoke the Execute privilege on a stored procedure from a role, that
role can no longer run that procedure.
Users cannot revoke roles from themselves. When you revoke a role, you
cannot revoke the WITH GRANT OPTION separately. If the role was granted
with the WITH GRANT OPTION, both the role and grant option are revoked.
The following example revokes the engineer role from the user maryf:
REVOKE engineer FROM maryf
Revoking Privileges Granted from WITH GRANT OPTION
If you revoke from user the privileges that you granted using the WITH
GRANT OPTION keywords, you sever the chain of privileges granted by that
user. In this case, when you revoke privileges from user, you automatically
revoke the privileges of all users who received privileges from user or from
the chain that user created. You can also specify this default condition with
the CASCADE keyword.
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Informix Guide to SQL: Syntax
REVOKE
Controlling the Scope of a REVOKE with the RESTRICT Option
Use the RESTRICT keyword to control the success or failure of the REVOKE
command based on the existence of dependencies on the objects that are
being revoked. The following list shows the dependencies that cause the
REVOKE statement to fail when you use the RESTRICT keyword:
■
The user from whom the privilege is to be revoked has granted this
privilege to another user or users.
■
A view depends on a Select privilege that is being revoked.
■
A foreign-key constraint depends on a References privilege that is
being revoked.
Failure of the REVOKE When the Revokee Has Granted a Privilege
A REVOKE statement with the RESTRICT keyword fails if the user from whom
a privilege is being revoked has granted the same privilege to another user or
users. However, the same REVOKE statement does not fail if the revokee has
the right to grant the privilege to other users but has not actually granted the
privilege to any other user. We can illustrate these points by means of
examples.
Assume that the user clara has granted the Select privilege on the customer
table to the user ted, and she has also granted user ted the right to grant the
Select privilege to other users. User ted has used this authority to grant the
Select privilege on the customer table to the user named tania. Now user
clara attempts to revoke the Select privilege from user ted with the following
REVOKE statement:
REVOKE SELECT ON customer FROM ted RESTRICT
This statement fails because user ted has granted the Select privilege to user
tania.
SQL Statements 1-441
REVOKE
What if the revokee has the right to grant the privilege to other users but has
not actually granted this privilege to any other user? For example, assume
that the user clara has granted the Select privilege on the customer table to
the user roger, and she has also granted user roger the right to grant the Select
privilege to other users. However, user roger has not used this authority to
granted the Select privilege to any other user. Now user clara attempts to
revoke the Select privilege from user roger with the following REVOKE
statement:
REVOKE SELECT ON customer FROM roger RESTRICT
This statement succeeds because user roger has not granted the Select
privilege to any other user.
REVOKE and ROLLBACK WORK
SE
You cannot use a ROLLBACK WORK statement to undo a REVOKE statement
that successfully executes. If you roll back a transaction that contains a
REVOKE statement, the privilege is not granted again to the user, and you do
not receive an error message. ♦
Table-Level Privileges
Table-Level
Privileges
ALL
PRIVILEGES
,
INSERT
DELETE
SELECT
UPDATE
INDEX
ALTER
REFERENCES
1-442
Informix Guide to SQL: Syntax
REVOKE
To revoke a table-level privilege from a user, you must revoke all occurrences
of the privilege. For example, if two users grant the same privilege to a user,
both of them must revoke the privilege. If one grantor revokes the privilege,
the user retains the privilege received from the other grantor. (The database
server keeps a record of each table-level grant in the syscolauth and
systabauth system catalog tables.)
If a table owner grants a privilege to PUBLIC, the owner cannot revoke the
same privilege from any particular user. For example, if the table owner
grants the Select privilege to PUBLIC and then attempts to revoke the Select
privilege from mary, the REVOKE statement generates an error. The Select
privilege was granted to PUBLIC, not to mary, and therefore the privilege
cannot be revoked from mary. (ISAM error number 111, No record found,
refers to the lack of a record in either the syscolauth or systabauth system
catalog table, which would represent the grant that the table owner now
wants to revoke.)
You can revoke table-level privileges individually or in combination. List the
keywords that correspond to the privileges that you are revoking from user.
The keywords are described in the following list. Unlike the GRANT statement, the REVOKE statement does not allow you to qualify the Select,
Update, or References privilege with a column name. Thus you cannot
revoke access on specific columns.
Privilege
Functions
INSERT
Provides the ability to insert rows
DELETE
Provides the ability to delete rows
SELECT
Provides the ability to display data obtained from a SELECT
statement
UPDATE
Provides the ability to change column values
INDEX
Provides the ability to create permanent indexes. You must
have the Resource privilege to take advantage of the Index
privilege. (Any user with the Connect privilege can create
indexes on temporary tables.)
(1 of 2)
SQL Statements 1-443
REVOKE
Privilege
Functions
ALTER
Provides the ability to add or delete columns, modify column
data types, and add or delete constraints. This privilege also
provides the ability to set the object mode of unique indexes
and constraints to the enabled, disabled, or filtering mode. In
addition, this privilege provides the ability to set the object
mode of non-unique indexes and triggers to the enabled or
disabled modes.
REFERENCES
Provides the ability to reference columns in referential
constraints. You must have the Resource privilege to take
advantage of the References privilege. (However, you can add
a referential constraint during an ALTER TABLE statement.
This method does not require that you have the Resource
privilege on the database.) Revoke the References privilege to
disallow cascading deletes.
ALL
Provides all the preceding privileges. The PRIVILEGES
keyword is optional.
(2 of 2)
Behavior of the ALL Keyword
The ALL keyword revokes all table-level privileges. If any or all of the
table-level privileges do not exist for the revokee, the REVOKE statement with
the ALL keyword executes successfully but returns the following SQLSTATE
code:
01006 - Privilege not revoked
For example, assume that the user hal has the Select and Insert privileges on
the customer table. User jocelyn wants to revoke all seven table-level privileges from user hal. So user jocelyn issues the following REVOKE statement:
REVOKE ALL ON customer FROM hal
1-444
Informix Guide to SQL: Syntax
REVOKE
Only a user with the DBA privilege can grant or revoke database-level
privileges.
Three levels of database privileges control access. These privilege levels are,
from lowest to highest, Connect, Resource, and DBA. To revoke a database
privilege, specify one of the keywords CONNECT, RESOURCE, or DBA in the
REVOKE statement.
Because of the hierarchical organization of the privileges (as outlined in the
privilege definitions that are described later in this section), if you revoke
either the Resource or the Connect privilege from a user with the DBA privilege, the statement has no effect. If you revoke the DBA privilege from a user
who has the DBA privilege, the user retains the Connect privilege on the database. To deny database access to a user with the DBA or Resource privilege,
you must first revoke the DBA or the Resource privilege and then revoke the
Connect privilege in a separate REVOKE statement.
Similarly, if you revoke the Connect privilege from a user with the Resource
privilege, the statement has no effect. If you revoke the Resource privilege
from a user, the user retains the Connect privilege on the database.
The database privileges are associated with the following keywords.
1-446
Informix Guide to SQL: Syntax
REVOKE
Privilege
Functions
CONNECT
Lets you query and modify data. You can modify the database
schema if you won the object that you want to modify. Any user
with the Connect privilege can perform the following functions:
RESOURCE
■
Connect to the database with the CONNECT statement or
another connection statement
■
Execute SELECT, INSERT, UPDATE, and DELETE statements, provided that the user has the necessary table-level privileges
■
Create views, provided that the user has the Select privilege on
the underlying tables
■
Create synonyms
■
Create temporary tables, and create indexes on the temporary
tables
■
Alter or drop a table or an index, provided that the user owns the
table or index (or has the Alter, Index, or References privilege on
the table)
■
Grant privileges on a table, provided that the user owns the table
(or has been given privileges on the table with the WITH GRANT
OPTION keyword)
Lets you extend the structure of the database. In addition to the
capabilities of the Connect privilege, the holder of the Resource
privilege can perform the following functions:
■
Create new tables
■
Create new indexes
■
Create new procedures
(1 of 2)
SQL Statements 1-447
REVOKE
Privilege
Functions
DBA
Lets the holder of DBA privilege perform the following functions
in addition to the capabilities of the Resource privilege:
SE
■
Grant any database-level privilege, including the DBA privilege,
to another user
■
Grant any table-level privilege to another user
■
Grant any table-level privilege to a role
■
Grant a role to a user or to another role
■
Execute the SET SESSION AUTHORIZATION statement
■
Use the NEXT SIZE keyword to alter extent sizes in the system
catalog tables
■
Drop any object, regardless of who owns it
■
Create tables, views, and indexes as well as specify another user
as owner of the objects
■
Execute the DROP DATABASE statement
■
Execute the START DATABASE and ROLLFORWARD DATABASE
statements♦
■
Insert, delete, or update rows of any system catalog table except
systables
(2 of 2)
Warning: Although the user informix and DBAs can modify most system catalog
tables (only the user informix can modify systables), Informix strongly recommends that you do not update, delete, or insert any rows in these tables. Modifying
the system catalog tables can destroy the integrity of the database. Informix does
support use of the ALTER TABLE statement to modify the size of the next extent of
system catalog tables.
1-448
Informix Guide to SQL: Syntax
REVOKE
References
See the GRANT, GRANT FRAGMENT, and REVOKE FRAGMENT statements in
this manual.
For information about roles, see the CREATE ROLE, DROP ROLE, and SET
ROLE statements in this manual.
See the discussion of privileges and security in the Informix Guide to SQL:
Tutorial.
SQL Statements 1-449
REVOKE FRAGMENT
REVOKE FRAGMENT
The REVOKE FRAGMENT statement enables you to revoke privileges that
have been granted on individual fragments of a fragmented table. You can
use this statement to revoke the Insert, Update, and Delete fragment-level
privileges from users.
Syntax
OL
+
REVOKE
FRAGMENT
Fragment-Level
Privileges
p. 1-452
ON
tablename
,
FROM
,
(
1-450
Informix Guide to SQL: Syntax
dbspace
user
'user '
)
REVOKE FRAGMENT
Element
Purpose
Restrictions
Syntax
dbspace
The name of the dbspace where
the fragment is stored. Use this
parameter to specify the
fragment or fragments on which
privileges are to be revoked. If
you do not specify a fragment,
the REVOKE statement applies to
all fragments in the specified
table that have the specified
privileges.
The name of the table that
contains the fragment or
fragments on which privileges
are to be revoked. There is no
default value.
The name of the user or users
from whom the specified
privileges are to be revoked.
There is no default value.
The specified dbspace or
dbspaces must exist.
Identifier, p. 1-723
The specified table must exist
and must be fragmented by
expression.
Table Name, p. 1-768
The user must be a valid user.
Identifier, p. 1-723
tablename
user
Usage
Use the REVOKE FRAGMENT statement to revoke the Insert, Update, or
Delete privilege on one or more fragments of a fragmented table from one or
more users.
The REVOKE FRAGMENT statement is only valid for tables that are
fragmented according to an expression-based distribution scheme. See the
ALTER FRAGMENT statement on page 1-22 for an explanation of expressionbased distribution schemes.
You can specify one fragment or a list of fragments in the REVOKE
FRAGMENT statement. To specify a fragment, name the dbspace in which the
fragment resides.
You do not have to specify a particular fragment or a list of fragments in the
REVOKE FRAGMENT statement. If you do not specify any fragments in the
statement, the specified users lose the specified privileges on all fragments
for which the users currently have those privileges.
SQL Statements 1-451
REVOKE FRAGMENT
Fragment-Level Privileges
Fragment-Level
Privileges
ALL
,
INSERT
DELETE
UPDATE
You can revoke fragment-level privileges individually or in combination. List
the keywords that correspond to the privileges that you are revoking from
user. The keywords are described in the following list.
Privilege
Functions
ALL
Revokes all privileges currently granted on a table fragment
INSERT
Revokes Insert privilege on a table fragment. This privilege gives
the user the ability to insert rows in the fragment.
DELETE
Revokes Delete privilege on a table fragment. This privilege gives
the user the ability to delete rows in the fragment.
UPDATE
Revokes Update privilege on a table fragment. This privilege gives
the user the ability to update rows in the fragment and to name any
column of the table in an UPDATE statement.
If you specify the ALL keyword in a REVOKE FRAGMENT statement, the
specified users lose all fragment-level privileges that they currently have on
the specified fragments.
For example, assume that a user currently has the Update privilege on one
fragment of a table. If you use the ALL keyword to revoke all current privileges on this fragment from this user, the user loses the Update privilege that
he or she had on this fragment.
1-452
Informix Guide to SQL: Syntax
REVOKE FRAGMENT
Examples of the REVOKE FRAGMENT Statement
The examples that follow are based on the customer table. All the examples
assume that the customer table is fragmented by expression into three
fragments that reside in the dbspaces that are named dbsp1, dbsp2, and
dbsp3.
Revoking One Privilege
The following statement revokes the Update privilege on the fragment of the
customer table in dbsp1 from the user ed:
REVOKE FRAGMENT UPDATE ON customer (dbsp1) FROM ed
Revoking More Than One Privilege
The following statement revokes the Update and Insert privileges on the
fragment of the customer table in dbsp1 from the user susan:
REVOKE FRAGMENT UPDATE, INSERT ON customer (dbsp1) FROM susan
Revoking All Privileges
The following statement revokes all privileges currently granted to the user
harry on the fragment of the customer table in dbsp1.:
REVOKE FRAGMENT ALL ON customer (dbsp1) FROM harry
Revoking Privileges on More Than One Fragment
The following statement revokes all privileges currently granted to the user
millie on the fragments of the customer table in dbsp1 and dbsp2:
REVOKE FRAGMENT ALL ON customer (dbsp1, dbsp2) FROM millie
Revoking Privileges from More Than One User
The following statement revokes all privileges currently granted to the users
jerome and hilda on the fragment of the customer table in dbsp3:
REVOKE FRAGMENT ALL ON customer (dbsp3) FROM jerome, hilda
SQL Statements 1-453
REVOKE FRAGMENT
Revoking Privileges Without Specifying Fragments
The following statement revokes all current privileges from the user mel on
all fragments for which this user currently has privileges:
REVOKE FRAGMENT ALL ON customer FROM mel
References
See the REVOKE and GRANT FRAGMENT statements in this manual.
1-454
Informix Guide to SQL: Syntax
ROLLBACK WORK
ROLLBACK WORK
Use the ROLLBACK WORK statement to cancel a transaction and undo any
changes that occurred since the beginning of the transaction.
Syntax
ROLLBACK
WORK
Usage
The ROLLBACK WORK statement is valid only in databases with transactions.
In a database that is not ANSI-compliant, start a transaction with a BEGIN
WORK statement. You can end a transaction with a COMMIT WORK statement
or cancel the transaction with a ROLLBACK WORK statement. The ROLLBACK
WORK statement restores the database to the state that existed before the
transaction began. Use the ROLLBACK WORK statement only at the end of a
multistatement operation.
The ROLLBACK WORK statement releases all row and table locks that the
cancelled transaction holds. If you issue a ROLLBACK WORK statement when
no transaction is pending, an error occurs.
ANSI
SE
In an ANSI-compliant database, transactions are implicit. Transactions start
after each COMMIT WORK or ROLLBACK WORK statement. If you issue a
ROLLBACK WORK statement when no transaction is pending, the statement
is accepted but has no effect. ♦
A ROLLBACK WORK statement undoes all database changes except those that
result from GRANT or REVOKE statements or from data definition statements.
Data definition statements are treated as single transactions. If they execute
successfully, they are committed automatically and cannot be rolled back by
the ROLLBACK WORK statement. Data definition statements include statements that modify the number, names, or indexes of tables and statements
that modify the number, names, or data types of columns. For a list of data
definition statements, see “Data Definition Statements” on page 1-12.
SQL Statements 1-455
ROLLBACK WORK
If a transaction rolls back, the actions that are taken to undo the transaction
are also logged to table audit trails, if any exist. ♦
ESQL
The ROLLBACK WORK statement closes all open cursors except those that are
declared with hold, which remain open despite transaction activity.
If you use the ROLLBACK WORK statement within a routine that a
WHENEVER statement calls, specify WHENEVER SQLERROR CONTINUE and
WHENEVER SQLWARNING CONTINUE before the ROLLBACK WORK
statement. This prevents the program from looping if the ROLLBACK WORK
statement encounters an error or a warning. ♦
References
See the BEGIN WORK and COMMIT WORK statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of ROLLBACK WORK
in Chapter 5.
1-456
Informix Guide to SQL: Syntax
ROLLFORWARD DATABASE
ROLLFORWARD DATABASE
Use the ROLLFORWARD DATABASE statement with the INFORMIX-SE
database server to apply the transaction log file to a restored database.
Syntax
SE
+
ROLLFORWARD DATABASE
Database
Name
p. 1-660
Usage
To restore a database, you need both the archive copy of the database and the
transaction log that began immediately after the archive copy was made.
To execute the ROLLFORWARD DATABASE statement, you need the DBA
privilege. Always precede a ROLLFORWARD DATABASE statement with a
CLOSE DATABASE statement. The ROLLFORWARD DATABASE statement fails
if a database is open.
The ROLLFORWARD DATABASE statement sets an exclusive lock on the
database to prevent access by other processes. If another process is using the
database (even if the database is only being read), the ROLLFORWARD
DATABASE statement fails.
The database remains locked after the ROLLFORWARD DATABASE statement
executes. This allows you to check for errors before you give access to other
users. When you are satisfied that the database is ready for use, issue the
CLOSE DATABASE statement to release the exclusive lock. You can open the
database with the DATABASE statement.
You must be working on a database server to issue a ROLLFORWARD
DATABASE statement. You cannot execute the statement from a client
computer.
SQL Statements 1-457
ROLLFORWARD DATABASE
References
See the BEGIN WORK, COMMIT WORK, CLOSE DATABASE, DATABASE, and
ROLLBACK WORK statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of backups and logs
in Chapter 4.
1-458
Informix Guide to SQL: Syntax
SELECT
SELECT
Use the SELECT statement to query a database.
Syntax
UNION
UNION ALL
SELECT
Select
Clause
p. 1-461
FROM
Clause
p. 1-472
ESQL
SPL
INTO
Clause
p. 1-467
WHERE
Clause
p. 1-474
ORDER BY
Clause
p. 1-487
HAVING
Clause
p. 1-485
+
+
INTO TEMP
Clause
p. 1-495
FOR READ ONLY
FOR UPDATE
,
OF
Element
column name
GROUP BY
Clause
p. 1-483
Purpose
The name of a column that can
be updated after a fetch
column
name
Restrictions
Syntax
The specified column must be in Identifier, p. 1-723
the table, but it does not have to
be in the select list of the SELECT
clause.
SQL Statements 1-459
SELECT
Usage
You can query the tables in the current database, a database that is not
current, or a database that is on a different database server from your current
database.
SE
You can query only the current database. ♦
The SELECT statement comprises many basic clauses. Each clause is
described in the following list.
ESQL
Clause
Purpose
SELECT
Names a list of items to be read from the database
INTO
Specifies the program variables or host variables that
receive the selected data ♦
FROM
Names the tables that contain the selected columns
WHERE
Sets conditions on the selected rows
GROUP BY
Combines groups of rows into summary results
HAVING
Sets conditions on the summary results
ORDER BY
Orders the selected rows
INTO TEMP
Creates a temporary table in the current database and
puts the results of the query into the table
FOR UPDATE
Specifies that the values returned by the SELECT
statement can be updated after a fetch
FOR READ ONLY
Specifies that the values returned by the SELECT
statement cannot be updated after a fetch
SPL
1-460
Informix Guide to SQL: Syntax
SELECT
SELECT Clause
The SELECT clause contains the list of database objects or expressions to be
selected, as shown in the following diagram.
,
Select
Clause
Select
List
ALL
+
DISTINCT
UNIQUE
Select
List
Expression
p. 1-671
display
label
AS
*
Table
Name
p. 1-768
.
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
SQL Statements 1-461
SELECT
Element
*
Purpose
The asterisk (*) signifies that all
columns in the specified table or
view are to be selected.
display label
A temporary name that you
assign to a column. In DB-Access,
the display label appears as the
heading for the column in the
output of the SELECT statement.
In ESQL, the value of display label
is stored in the sqlname field of
the sqlda structure. For more
information on the display label
parameter, see “Using a Display
Label” on page 1-466.
Restrictions
Use this symbol whenever you
want to retrieve all the columns
in the table or view in their
defined order. If you want to
retrieve all the columns in some
other order, or if you want to
retrieve a subset of the columns,
you must specify the columns
explicitly in the SELECT list.
You can assign a display label to
any column in your select list. If
you are creating a temporary
table with the SELECT...INTO
TEMP clause, you must supply a
display label for any columns
that are not simple column
expressions. The display label is
used as the name of the column
in the temporary table. If you are
using the SELECT statement in
creating a view, do not use
display labels. Specify the
desired label names in the
CREATE VIEW column list
instead. If your display label is
also a keyword, you can use the
AS keyword with the display
label to clarify the use of the
word. You must use the AS
keyword with the display label
to use any of the following
words as a display label: UNITS,
Syntax
The asterisk (*) is a
literal value that has
a special meaning in
this statement.
Identifier, p. 1-723
YEAR, MONTH, DAY, HOUR,
MINUTE, SECOND, or FRACTION.
In the SELECT clause, specify exactly what data is being selected as well as
whether you want to omit duplicate values.
1-462
Informix Guide to SQL: Syntax
SELECT
Allowing Duplicates
You can apply the ALL, UNIQUE, or DISTINCT keywords to indicate whether
duplicate values are returned, if any exist. If you do not specify any
keywords, all the rows are returned by default.
Keyword
Meaning
ALL
Specifies that all selected values are returned, regardless of
whether duplicates exist. ALL is the default state.
DISTINCT
Eliminates duplicate rows from the query results
UNIQUE
Eliminates duplicate rows from the query results. UNIQUE is a
synonym for DISTINCT.
For example, the following query lists the stock_num and manu_code of all
items that have been ordered, excluding duplicate items:
SELECT DISTINCT stock_num, manu_code FROM items
You can use the DISTINCT or UNIQUE keywords once in each level of a query
or subquery. For example, the following query uses DISTINCT in both the
query and the subquery:
SELECT DISTINCT stock_num, manu_code FROM items
WHERE order_num = (SELECT DISTINCT order_num FROM orders
WHERE customer_num = 120)
Expressions in the Select List
You can use any basic type of expression (column, constant, function,
aggregate function, and stored procedure), or combination thereof, in the
select list. The expression types are described in “Expression” on page 1-671.
The following sections present examples of using each type of simple
expression in the select list.
You can combine simple numeric expressions by connecting them with
arithmetic operators for addition, subtraction, multiplication, and division.
However, if you combine a column expression and an aggregate function,
you must include the column expression in the GROUP BY clause.
SQL Statements 1-463
SELECT
You cannot use variable names (for example, host variables in an ESQL
application or stored procedure variables in a stored procedure) in the select
list by themselves. You can include a variable name in the select list, however,
if an arithmetic or concatenation operator connects it to a constant.
Selecting Columns
Column expressions are the most commonly used expressions in a SELECT
statement. See “Column Expressions” on page 1-673 for a complete
description of the syntax and use of column expressions.
The following examples show column expressions within a select list:
SELECT orders.order_num, items.price FROM orders, items
SELECT customer.customer_num ccnum, company FROM customer
SELECT catalog_num, stock_num, cat_advert [1,15] FROM catalog
SELECT lead_time - 2 UNITS DAY FROM manufact
Selecting Constants
If you include a constant expression in the select list, the same value is
returned for each row that the query returns. See “Constant Expressions” on
page 1-676 for a complete description of the syntax and use of constant
expressions.
The following examples show constant expressions within a select list:
SELECT 'The first name is', fname FROM customer
SELECT TODAY FROM cust_calls
SELECT SITENAME FROM systables WHERE tabid = 1
SELECT lead_time - 2 UNITS DAY FROM manufact
SELECT customer_num + LENGTH('string') from customer
Selecting Function Expressions
A function expression uses a function that is evaluated for each row in the
query. All function expressions require arguments. This set of expressions
contains the time functions and the length function when they are used with
a column name as an argument.
1-464
Informix Guide to SQL: Syntax
SELECT
Selecting Expressions That Use Arithmetic Operators
You can combine numeric expressions with arithmetic operators to make
complex expressions. You cannot combine expressions that contain
aggregate functions with column expressions. The following examples show
expressions that use arithmetic operators within a select list:
SELECT stock_num, quantity*total_price FROM customer
SELECT price*2 doubleprice FROM items
SELECT count(*)+2 FROM customer
SELECT count(*)+LENGTH('ab') FROM customer
Using a Display Label
If you are creating a temporary table, you must supply a display label for any
columns that are not simple column expressions. The display label is used as
the name of the column in the temporary table.
DB
ESQL
A display label appears as the heading for that column in the output of the
SELECT statement. ♦
The value of display label is stored in the sqlname field of the sqlda structure.
See your SQL API product manual for more information on the sqlda
structure. ♦
If you are using the SELECT statement in creating a view, do not use display
labels. Specify the desired label names in the CREATE VIEW column list
instead.
Using the AS Keyword
If your display label is also a keyword, you can use the AS keyword with the
display label to clarify the use of the word. If you want to use the word
UNITS, YEAR, MONTH, DAY, HOUR, MINUTE, SECOND, or FRACTION as your
display label, you must use the AS keyword with the display label. The
following example shows how to use the AS keyword with minute as a
display label:
SELECT call_dtime AS minute FROM cust_calls
1-466
Informix Guide to SQL: Syntax
SELECT
INTO Clause
Use the INTO clause within a stored procedure or SQL API to specify the
program variables or host variables to receive the data that the SELECT
statement retrieves. The following diagram shows the syntax of the INTO
clause.
INTO
Clause
,
INTO
data variable
ESQL
: indicator
variable
+
$ indicator
variable
INDICATOR
indicator variable
data structure
SQL Statements 1-467
SELECT
Element
data variable
Purpose
A program variable or host
object. This variable receives the
value of the corresponding item
in the select list of the SELECT
clause
data structure
A structure that has been
declared as a host variable
indicator
variable
A program variable that receives
a return code if null data is
placed in the corresponding data
variable
Restrictions
The order of receiving variables
in the INTO clause must match
the order of the corresponding
items in the select list of the
SELECT clause. The number of
receiving variables must be
equal to the number of items in
the select list. The data type of
each receiving variable should
agree with the data type of the
corresponding column or
expression in the select list. See
“Error Checking” on page 1-471
for the actions that the database
server takes when the data type
of the receiving variable does
not match that of the selected
item.
The individual elements of the
structure must be matched
appropriately to the data type of
values being selected.
This parameter is optional, but
you should use an indicator
variable if the possibility exists
that the value of the corresponding data variable is null.
Syntax
The name of the
receiving variable
must conform to
language-specific
rules for variable
names.
The name of the data
structure must
conform to
language-specific
rules for data
structures.
The name of the
indicator variable
must conform to
language-specific
rules for indicator
variables.
If the SELECT statement stands alone (that is, it is not part of a DECLARE
statement and does not use the INTO clause), it must be a singleton SELECT
statement. A singleton SELECT statement returns only one row. The following
example shows a singleton SELECT statement in INFORMIX-ESQL/C:
EXEC SQL select fname, lname, company_name
into :p_fname, :p_lname, :p_coname
where customer_num = 101;
1-468
Informix Guide to SQL: Syntax
SELECT
INTO Clause with Indicator Variables
ESQL
You should use an indicator variable if the possibility exists that data
returned from the SELECT statement is null. See your SQL API product
manual for more information about indicator variables.
INTO Clause with Cursors
If the SELECT statement returns more than one row, you must use a cursor in
a FETCH statement to fetch the rows individually. You can put the INTO
clause in the FETCH statement rather than in the SELECT statement, but you
cannot put it in both.
The following INFORMIX-ESQL/C code examples show different ways you
can use the INTO clause:
Using the INTO clause in the SELECT statement
EXEC SQL declare q_curs cursor for
select lname, company
into :p_lname, :p_company
from customer;
EXEC SQL open q_curs;
while (SQLCODE == 0)
EXEC SQL fetch q_curs;
EXEC SQL close q_curs;
Using the INTO clause in the FETCH statement
EXEC SQL declare q_curs cursor for
select lname, company
from customer;
EXEC SQL open q_curs;
while (SQLCODE == 0)
EXEC SQL fetch q_curs into :p_lname, :p_company;
EXEC SQL close q_curs;
SQL Statements 1-469
SELECT
Preparing a SELECT...INTO Query
You cannot prepare a query that has an INTO clause. You can prepare the
query without the INTO clause, declare a cursor for the prepared query, open
the cursor, and then use the FETCH statement with an INTO clause to fetch the
cursor into the program variable. Alternatively, you can declare a cursor for
the query without first preparing the query and include the INTO clause in
the query when you declare the cursor. Then open the cursor, and fetch the
cursor without using the INTO clause of the FETCH statement.
Using Array Variables with the INTO Clause
If you use a DECLARE statement with a SELECT statement that contains an
INTO clause, and the program variable is an array element, you can identify
individual elements of the array with integer constants or with variables. The
value of the variable that is used as a subscript is determined when the cursor
is declared, so afterward the subscript variable acts as a constant.
The following INFORMIX-ESQL/C code example declares a cursor for a
SELECT...INTO statement using the variables i and j as subscripts for the array
a. After you declare the cursor, the INTO clause of the SELECT statement is
equivalent to INTO a[5], a[2].
i = 5
j = 2
EXEC SQL declare c cursor for
select order_num, po_num into :a[i], :a[j] from orders
where order_num =1005 and po_num =2865
You can also use program variables in the FETCH statement to specify an
element of a program array in the INTO clause. With the FETCH statement, the
program variables are evaluated at each fetch rather than when you declare
the cursor. ♦
1-470
Informix Guide to SQL: Syntax
SELECT
Error Checking
ESQL
If the number of variables that are listed in the INTO clause differs from the
number of items in the SELECT clause, a warning is returned in the sqlwarn
structure; the following diagram shows the specific structure name. The
actual number of variables that are transferred is the lesser of the two
numbers. See your SQL API product manual for information about the
sqlwarn structure.
Product Name
Variable Name
ESQL/C
sqlca.sqlwarn.sqlwarn3
ESQL/COBOL
SQLWARN3 OF SQLWARN OF SQLCA
♦
ANSI
ESQL
SPL
If the number of variables that are listed in the INTO clause differs from the
number of items in the SELECT clause, you receive an error. ♦
If the data type of the receiving variable does not match that of the selected
item, the data type of the selected item is converted, if possible. If the
conversion is impossible, an error occurs, and a negative value is returned in
the status variable. In this case, the value in the program variable is unpredictable. The following table shows the specific name of the status variable
for each application development tool.
Product Name
Variable Name
ESQL/C
sqlca.sqlcode, SQLCODE
ESQL/COBOL
SQLCODE OF SQLCA
♦
SQL Statements 1-471
SELECT
FROM Clause
The FROM clause lists the table or tables from which you are selecting the
data. The following diagram shows the syntax of the FROM clause.
FROM
Clause
Table
Name
p. 1-768
FROM
+
Additional
Tables
AS
Synonym
Name
p. 1-766
Additional
Tables
,
alias
View
Name
p. 1-772
,
Table
Name
p. 1-768
alias
View
Name
p. 1-772
+
+
AS
Synonym
Name
p. 1-766
OUTER
Table
Name
p. 1-768
alias
View
Name
p. 1-772
AS
Synonym
Name
p. 1-766
OUTER
(
Table
Name
p. 1-768
View
Name
p. 1-772
Synonym
Name
p. 1-766
1-472
Informix Guide to SQL: Syntax
)
alias
AS
,
Additional
Tables
SELECT
Element
alias
Purpose
A temporary alternative name
for a table or view within the
scope of a SELECT statement.
You can use aliases to make a
query shorter.
Restrictions
Syntax
If the SELECT statement is a self- Identifier, p. 1-723
join, you must list the table name
twice in the FROM clause and
assign a different alias to each
occurrence of the table name. If
you use a potentially ambiguous
word as an alias, you must
precede the alias with the
keyword AS. See “AS Keyword
with Aliases” on page 1-474 for
further information on this
restriction.
Use the keyword OUTER to form outer joins. Outer joins preserve rows that
otherwise would be discarded by simple joins. See Chapter 3 of the Informix
Guide to SQL: Tutorial for more information on outer joins.
You can supply an alias for a table name or view name. You can use the alias
to refer to the table or view in other clauses of the SELECT statement. This is
especially useful with a self-join. (See the WHERE clause on page 1-474 for
more information about self-joins.)
The following example shows typical uses of the FROM clause. The first
query selects all the columns and rows from the customer table. The second
query uses a join between the customer and orders table to select all the
customers who have placed orders.
SELECT * FROM customer
SELECT fname, lname, order_num
FROM customer, orders
WHERE customer.customer_num = orders.customer_num
The following example is the same as the second query in the preceding
example, except that it establishes aliases for the tables in the FROM clause
and uses them in the WHERE clause:
SELECT fname, lname, order_num
FROM customer c, orders o
WHERE c.customer_num = o.customer_num
SQL Statements 1-473
SELECT
The following example uses the OUTER keyword to create an outer join and
produce a list of all customers and their orders, regardless of whether they
have placed orders:
SELECT customer.customer_num, lname, order_num
FROM customer c, OUTER orders o
WHERE c.customer_num = o.customer_num
AS Keyword with Aliases
To use potentially ambiguous words as an alias for a table or view, you must
precede them with the keyword AS. Use the AS keyword if you want to use
the words ORDER, FOR, AT, GROUP, HAVING, INTO, UNION, WHERE, WITH,
CREATE, or GRANT as an alias for a table or view.
WHERE Clause
Use the WHERE clause to specify search criteria and join conditions on the
data that you are selecting.
WHERE
Clause
AND
Condition
p. 1-643
WHERE
Join
p. 1-480
Using a Condition in the WHERE Clause
You can use the following kinds of simple conditions or comparisons in the
WHERE clause:
1-474
■
Relational-operator condition
■
BETWEEN
■
IN
■
IS NULL
■
LIKE or MATCHES
Informix Guide to SQL: Syntax
SELECT
You also can use a SELECT statement within the WHERE clause; this is called
a subquery. The following list contains the kinds of subquery WHERE
clauses:
■
IN
■
EXISTS
■
ALL/ANY/SOME
Examples of each type of condition are shown in the following sections. For
more information about each kind of condition, see the Condition segment
on page 1-643.
You cannot use an aggregate function in the WHERE clause unless it is part of
a subquery or if the aggregate is on a correlated column originating from a
parent query and the WHERE clause is within a subquery that is within a
HAVING clause.
Relational-Operator Condition
For a complete description of the relational-operator condition, see page
1-647.
A relational-operator condition is satisfied when the expressions on either
side of the relational operator fulfill the relation that the operator set up. The
following SELECT statements use the greater than (>) and equal (=) relational
operators:
SELECT order_num FROM orders
WHERE order_date > '6/04/94'
SELECT fname, lname, company
FROM customer
WHERE city[1,3] = 'San'
SQL Statements 1-475
SELECT
BETWEEN Condition
For a complete description of the BETWEEN condition, see page 1-648.
The BETWEEN condition is satisfied when the value to the left of the
BETWEEN keyword lies in the inclusive range of the two values on the right
of the BETWEEN keyword. The first two queries in the following example use
literal values after the BETWEEN keyword. The third query uses the
CURRENT function and a literal interval. It looks for dates between the
current day and seven days earlier.
SELECT stock_num, manu_code FROM stock
WHERE unit_price BETWEEN 125.00 AND 200.00
SELECT DISTINCT customer_num, stock_num, manu_code
FROM orders, items
WHERE order_date BETWEEN '6/1/93' AND '9/1/93'
SELECT * FROM cust_calls WHERE call_dtime
BETWEEN (CURRENT - INTERVAL(7) DAY TO DAY) AND CURRENT
IN Condition
For a complete description of the IN condition, see page 1-653.
The IN condition is satisfied when the expression to the left of the IN keyword
is included in the list of values to the right of the keyword. The following
examples show the IN condition:
SELECT lname, fname, company
FROM customer
WHERE state IN ('CA','WA', 'NJ')
SELECT * FROM cust_calls
WHERE user_id NOT IN (USER )
IS NULL Condition
For a complete description of the IS NULL condition, see page 1-649.
The IS NULL condition is satisfied if the column contains a null value. If you
use the NOT option, the condition is satisfied when the column contains a
value that is not null. The following example selects the order numbers and
customer numbers for which the order has not been paid:
SELECT order_num, customer_num FROM orders
WHERE paid_date IS NULL
1-476
Informix Guide to SQL: Syntax
SELECT
LIKE or MATCHES Condition
For a complete description of the LIKE or MATCHES condition, see page 1-649.
The LIKE or MATCHES condition is satisfied when either of the following tests
is true:
■
The value of the column that precedes the LIKE or MATCHES
keyword matches the pattern that the quoted string specifies. You
can use wildcard characters in the string.
■
The value of the column that precedes the LIKE or MATCHES
keyword matches the pattern that is specified by the column that
follows the LIKE or MATCHES keyword. The value of the column on
the right serves as the matching pattern in the condition.
The following SELECT statement returns all rows in the customer table in
which the lname column begins with the literal string 'Baxter'. Because
the string is a literal string, the condition is case sensitive.
SELECT * FROM customer WHERE lname LIKE 'Baxter%'
The following SELECT statement returns all rows in the customer table in
which the value of the lname column matches the value of the fname
column:
SELECT * FROM customer WHERE lname LIKE fname
The following examples use the LIKE condition with a wildcard. The first
SELECT statement finds all stock items that are some kind of ball. The second
SELECT statement finds all company names that contain a percent sign (%).
The backslash (\) is used as the standard escape character for the wildcard
percent sign (%). The third SELECT statement uses the ESCAPE option with
the LIKE condition to retrieve rows from the customer table in which the
company column includes a percent sign (%). The z is used as an escape
character for the wildcard percent sign (%).
SELECT stock_num, manu_code FROM stock
WHERE description LIKE '%ball'
SELECT * FROM customer
WHERE company LIKE '%\%%'
SELECT * FROM customer
WHERE company LIKE '%z%%' ESCAPE 'z'
SQL Statements 1-477
SELECT
The following example of a SELECT statement with an EXISTS subquery
returns the stock number and manufacturer code for every item that has
never been ordered (and is therefore not listed in the items table). It is appropriate to use an EXISTS subquery in this SELECT statement because you need
the correlated subquery to test both stock_num and manu_code in the items
table.
SELECT stock_num, manu_code FROM stock
WHERE NOT EXISTS
(SELECT stock_num, manu_code FROM items
WHERE stock.stock_num = items.stock_num AND
stock.manu_code = items.manu_code)
The preceding example would work equally well if you use a SELECT * in the
subquery in place of the column names because you are testing for the
existence of a row or rows.
ALL/ANY/SOME Subquery
For a complete description of the ALL/ANY/SOME subquery, see page 1-655.
In the following example, the SELECT statements return the order number of
all orders that contain an item whose total price is greater than the total price
of every item in order number 1023. The first SELECT statement uses the ALL
subquery, and the second SELECT statement produces the same result by
using the MAX aggregate function.
SELECT DISTINCT order_num FROM items
WHERE total_price > ALL (SELECT total_price FROM items
WHERE order_num = 1023)
SELECT DISTINCT order_num FROM items
WHERE total_price > SELECT MAX(total_price) FROM items
WHERE order_num = 1023)
The following SELECT statements return the order number of all orders that
contain an item whose total price is greater than the total price of at least one
of the items in order number 1023. The first SELECT statement uses the ANY
keyword, and the second SELECT statement uses the MIN aggregate function.
SELECT DISTINCT order_num FROM items
WHERE total_price > ANY (SELECT total_price FROM items
WHERE order_num = 1023)
SELECT DISTINCT order_num FROM items
WHERE total_price > (SELECT MIN(total_price) FROM items
WHERE order_num = 1023)
SQL Statements 1-479
SELECT
You can omit the keywords ANY, ALL, or SOME in a subquery if you know
that the subquery returns exactly one value. If you omit ANY, ALL, or SOME,
and the subquery returns more than one value, you receive an error. The
subquery in the following example returns only one row because it uses an
aggregate function:
SELECT order_num FROM items
WHERE stock_num = 9 AND quantity =
(SELECT MAX(quantity) FROM items WHERE stock_num = 9)
Using a Join in the WHERE Clause
You join two tables when you create a relationship in the WHERE clause
between at least one column from one table and at least one column from
another table. The effect of the join is to create a temporary composite table
where each pair of rows (one from each table) that satisfies the join condition
is linked to form a single row. You can create two-table joins, multiple-table
joins, and self-joins.
The following diagram shows the syntax for a join.
Join
column
name
1-480
Relational
Operator
p. 1-761
column
name
Table
Name
p. 1-768
.
Table
Name
p. 1-768
.
alias
.
alias
.
View
Name
p. 1-772
.
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
Synonym
Name
p. 1-766
.
Informix Guide to SQL: Syntax
SELECT
Element
alias
column name
Purpose
The alias assigned to the table or
view in the FROM clause. See
“FROM Clause” on page 1-472
for more information on aliases
for tables and views.
Restrictions
Syntax
If the tables to be joined are the Identifier, p. 1-723
same table (that is, if the join is a
self-join), you must refer to each
instance of the table in the
WHERE clause by the alias
assigned to that table instance in
the FROM clause.
The name of a column from one When the specified columns
Identifier, p. 1-723
of the tables or views to be
have the same name in the tables
joined. Rows from the tables or or views to be joined, you must
views are joined when there is a distinguish the columns by
match between the values of the preceding each column name
specified columns.
with the name or alias of the
table or view in which the
column resides.
Two-Table Joins
The following example shows a two-table join:
SELECT order_num, lname, fname
FROM customer, orders
WHERE customer.customer_num = orders.customer_num
Tip: You do not have to select the column where the two tables are joined.
Multiple-Table Joins
A multiple-table join is a join of more than two tables. Its structure is similar
to the structure of a two-table join, except that you have a join condition for
more than one pair of tables in the WHERE clause. When columns from
different tables have the same name, you must distinguish them by
preceding the name with its associated table or table alias, as in table.column.
See “Table Name” on page 1-768 for the full syntax of a table name.
SQL Statements 1-481
SELECT
The following multiple-table join yields the company name of the customer
who ordered an item as well as the stock number and manufacturer code of
the item:
SELECT DISTINCT company, stock_num, manu_code
FROM customer c, orders o, items i
WHERE c.customer_num = o.customer_num
AND o.order_num = i.order_num
Self-Joins
You can join a table to itself. To do so, you must list the table name twice in
the FROM clause and assign it two different table aliases. Use the aliases to
refer to each of the “two” tables in the WHERE clause.
The following example is a self-join on the stock table. It finds pairs of stock
items whose unit prices differ by a factor greater than 2.5. The letters x and y
are each aliases for the stock table.
SELECT x.stock_num, x.manu_code, y.stock_num, y.manu_code
FROM stock x, stock y
WHERE x.unit_price > 2.5 * y.unit_price
Outer Joins
The following outer join lists the company name of the customer and all
associated order numbers, if the customer has placed an order. If not, the
company name is still listed, and a null value is returned for the order
number.
SELECT company, order_num
FROM customer c, OUTER orders o
WHERE c.customer_num = o.customer_num
See Chapter 3 of the Informix Guide to SQL: Tutorial for more information
about outer joins.
1-482
Informix Guide to SQL: Syntax
SELECT
GROUP BY Clause
Use the GROUP BY clause to produce a single row of results for each group.
A group is a set of rows that have the same values for each column listed.
,
GROUP BY
Clause
column
name
GROUP BY
Table
Name
p. 1-768
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
alias
+
Element
alias
column name
Purpose
The alias assigned to a table or
view in the FROM clause. See
“FROM Clause” on page 1-472
for more information on aliases
for tables and views.
The name of a stand-alone
column in the select list of the
SELECT clause or the name of
one of the columns joined by an
arithmetic operator in the select
list. The SELECT statement
returns a single row of results for
each group of rows that have the
same value in column name.
.
select
number
Restrictions
Syntax
You cannot use an alias for a
Identifier, p. 1-723
table or view in the GROUP BY
clause unless you have assigned
the alias to the table or view in
the FROM clause.
See “Relationship of the GROUP Identifier, p. 1-723
BY Clause to the SELECT
Clause” on page 1-484.
(1 of 2)
SQL Statements 1-483
SELECT
Element
select number
Purpose
Restrictions
An integer that identifies a
See “Using Select Numbers” on
column or expression in the
page 1-485.
select list of the SELECT clause by
specifying its order in the select
list. The SELECT statement
returns a single row of results for
each group of rows that have the
same value in the column or
expression identified by select
number.
Syntax
Literal Number,
p. 1-752
(2 of 2)
Relationship of the GROUP BY Clause to the SELECT Clause
A GROUP BY clause restricts what you can enter in the SELECT clause. If you
use a GROUP BY clause, each column that you select must be in the GROUP BY
list. If you use an aggregate function and one or more column expressions in
the select list, you must put all the column names that are not used as part of
an aggregate or time expression in the GROUP BY clause. Do not put constant
expressions or BYTE or TEXT column expressions in the GROUP BY list. If you
are selecting a BYTE or TEXT column, you cannot use the GROUP BY clause. In
addition, you cannot use ROWID in a GROUP BY clause.
The following example names one column that is not in an aggregate
expression. The total_price column should not be in the GROUP BY list
because it appears as the argument of an aggregate function. The COUNT and
SUM keywords are applied to each group, not the whole query set.
SELECT order_num, COUNT(*), SUM(total_price)
FROM items
GROUP BY order_num
If a column stands alone in a column expression in the select list, you must
use it in the GROUP BY clause. If a column is combined with another column
by an arithmetic operator, you can choose to group by the individual
columns or by the combined expression using a specific number.
1-484
Informix Guide to SQL: Syntax
SELECT
Using Select Numbers
You can use one or more integers in the GROUP BY clause to stand for column
expressions. In the following example, the first SELECT statement uses select
numbers for order_date and paid_date - order_date in the GROUP BY clause.
Note that you can group only by a combined expression using the selectnumber notation. In the second SELECT statement, you cannot replace the 2
with the expression paid_date - order_date.
SELECT order_date, COUNT(*), paid_date - order_date
FROM orders
GROUP BY 1, 3
SELECT order_date, paid_date - order_date
FROM orders
GROUP BY order_date, 2
Nulls in the GROUP BY Clause
Each row that contains a null value in a column that is specified by a GROUP
BY clause belongs to a single group (that is, all null values are grouped
together).
HAVING Clause
Use the HAVING clause to apply one or more qualifying conditions to groups.
HAVING
Clause
HAVING
Condition
p. 1-643
SQL Statements 1-485
SELECT
ORDER BY Clause
Use the ORDER BY clause to sort query results by the values that are contained
in one or more columns.
ORDER BY
Clause
,
column
name
ORDER BY
Table
Name
p. 1-768
.
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
alias
.
+
ASC
[ first, last ]
DESC
select
number
+
display
label
ROWID
SQL Statements 1-487
SELECT
Element
alias
column name
display label
first
last
select number
1-488
Purpose
The alias assigned to a table or
view in the FROM clause. See
“FROM Clause” on page 1-472
for more information on aliases
for tables and views.
The name of a column in the
specified table or view. The
query results are sorted by the
values contained in this column.
Restrictions
You cannot specify an alias for a
table or view in the ORDER BY
clause unless you have assigned
the alias to the table or view in
the FROM clause.
A column specified in the
ORDER BY clause must be listed
explicitly or implicitly in the
select list of the SELECT clause. If
you want to order the query
results by a derived column, you
must supply a display label for
the derived column in the select
list and specify this label in the
ORDER BY clause. Alternatively,
you can omit a display label for
the derived column in the select
list and specify the derived
column by means of a select
number in the ORDER BY clause.
A temporary name that you
You cannot specify a display
assign to a column in the select label in the ORDER BY clause
list of the SELECT clause. You can unless you have specified this
use a display label in place of the display label for a column in the
column name in the ORDER BY select list.
clause.
The position of the first character The column must be one of the
in the portion of the column that following character types: BYTE,
is used to sort the query results CHAR, NCHAR, NVARCHAR,
TEXT, or VARCHAR.
The position of the last character The column must be one of the
in the portion of the column that following character types: BYTE,
is used to sort the query results CHAR, NCHAR, NVARCHAR,
TEXT, or VARCHAR.
An integer that identifies a
You must specify select numbers
column in the select list of the
in the ORDER BY clause when
SELECT clause by specifying its SELECT statements are joined by
UNION or UNION ALL keywords
order in the select list. You can
use a select number in place of a and compatible columns in the
column name in the ORDER BY same position have different
clause.
names.
Informix Guide to SQL: Syntax
Syntax
Identifier, p. 1-723
Identifier, p. 1-723
Identifier, p. 1-723
Literal Number,
p. 1-752
Literal Number,
p. 1-752
Literal Number,
p. 1-752
SELECT
You can perform an ORDER BY operation on a column or on an aggregate
expression when you use SELECT * or a display label in your SELECT
statement.
The following query explicitly selects the order date and shipping date from
the orders table and then rearranges the query by the order date. By default,
the query results are listed in ascending order.
SELECT order_date, ship_date FROM orders
ORDER BY order_date
In the following query, the order_date column is selected implicitly by the
SELECT * statement, so you can use order_date in the ORDER BY clause:
SELECT * FROM orders
ORDER BY order_date
Ordering by a Column Substring
You can order by a column substring instead of ordering by the entire length
of the column. The column substring is the portion of the column that the
database server uses for the sort. You define the column substring by specifying column subscripts (the first and last parameters). The column subscripts
represent the starting and ending character positions of the column
substring.
The following example shows a SELECT statement that queries the customer
table and specifies a column substring in the ORDER BY column. The column
substring instructs the database server to sort the query results by the portion
of the lname column contained in the sixth through ninth positions of the
column:
SELECT * from customer
ORDER BY lname[6,9]
Assume that the value of lname in one row of the customer table is
Greenburg. Because of the column substring in the ORDER BY clause, the
database server determines the sort position of this row by using the value
burg, not the value Greenburg.
You can specify column substrings only for columns that have a character
data type. If you specify a column substring in the ORDER BY clause, the
column must have one of the following data types: BYTE, CHAR, NCHAR,
NVARCHAR, TEXT, or VARCHAR.
SQL Statements 1-489
SELECT
GLS
For information on the GLS aspects of using column substrings in the ORDER
BY clause, see the Guide to GLS Functionality, Chapter 3. ♦
Ordering by a Derived Column
You can order by a derived column by supplying a display label in the
SELECT clause, as shown in the following example:
SELECT paid_date - ship_date span, customer_num
FROM orders
ORDER BY span
Ascending and Descending Orders
You can use the ASC and DESC keywords to specify ascending (smallest value
first) or descending (largest value first) order. The default order is ascending.
For DATE and DATETIME data types, smallest means earliest in time and
largest means latest in time. For standard character data types, the ASCII
collating sequence is used. See page 1-763 for a listing of the collating
sequence.
Nulls in the ORDER BY Clause
Null values are ordered as less than values that are not null. Using the ASC
order, the null value comes before the non-null value; using DESC order, the
null value comes last.
Nested Ordering
If you list more than one column in the ORDER BY clause, your query is
ordered by a nested sort. The first level of sort is based on the first column;
the second column determines the second level of sort. The following
example of a nested sort selects all the rows in the cust_calls table and orders
them by call_code and by call_dtime within call_code:
SELECT * FROM cust_calls
ORDER BY call_code, call_dtime
1-490
Informix Guide to SQL: Syntax
SELECT
Using Select Numbers
In place of column names, you can enter one or more integers that refer to the
position of items in the SELECT clause. You can use a select number to order
by an expression. For instance, the following example orders by the
expression paid_date - order_date and customer_num, using select numbers
in a nested sort:
SELECT order_num, customer_num, paid_date - order_date
FROM orders
ORDER BY 3, 2
Select numbers are required in the ORDER BY clause when SELECT statements
are joined by the UNION or UNION ALL keywords and compatible columns
in the same position have different names.
Ordering by Rowids
You can specify the rowid column as a column in the ORDER BY clause. The
rowid column is a hidden column in nonfragmented tables and in
fragmented tables that were created with the WITH ROWIDS clause. The
rowid column contains a unique internal record number that is associated
with a row in a table. Informix recommends, however, that you utilize
primary keys as an access method rather than exploiting the rowid column.
If you want to specify the rowid column in the ORDER BY clause, enter the
keyword ROWID in lowercase or uppercase letters.
You cannot specify the rowid column in the ORDER BY clause if the table you
are selecting from is a fragmented table that does not have a rowid column.
You cannot specify the rowid column in the ORDER BY clause unless you
have included the rowid column in the select list of the SELECT clause.
For further information on using the rowid column in column expressions,
see “Expression” on page 1-671.
ORDER BY Clause with DECLARE
ESQL
You cannot use a DECLARE statement with a FOR UPDATE clause to associate
a cursor with a SELECT statement that has an ORDER BY clause. ♦
SQL Statements 1-491
SELECT
Placing Indexes on ORDER BY Columns
When you include an ORDER BY clause in a SELECT statement, you can
improve the performance of the query by creating an index on the column or
columns that the ORDER BY clause specifies. The database server uses the
index that you placed on the ORDER BY columns to sort the query results in
the most efficient manner. For further information on creating indexes that
correspond to the columns of an ORDER BY clause, see “The ASC and DESC
Keywords” on page 1-113 under the CREATE INDEX statement.
FOR UPDATE Clause
Use the FOR UPDATE clause when you prepare a SELECT statement, and you
intend to update the values returned by the SELECT statement when the
values are fetched. Preparing a SELECT statement that contains a FOR
UPDATE clause is equivalent to preparing the SELECT statement without the
FOR UPDATE clause and then declaring a FOR UPDATE cursor for the
prepared statement.
The FOR UPDATE keyword notifies the database server that updating is
possible, causing it to use more-stringent locking than it would with a select
cursor. You cannot modify data through a cursor without this clause. You can
specify particular columns that can be updated.
After you declare a cursor for a SELECT... FOR UPDATE statement, you can
update or delete the currently selected row using an UPDATE or DELETE
statement with the WHERE CURRENT OF clause. The words CURRENT OF
refer to the row that was most recently fetched; they replace the usual test
expressions in the WHERE clause.
To update rows with a particular value, your program might contain statements such as the sequence of statements shown in the following example:
EXEC SQL
char
char
EXEC
.
.
.
BEGIN DECLARE SECTION;
fname[ 16];
lname[ 16];
SQL END DECLARE SECTION;
EXEC SQL connect to 'stores7';
/* select statement being prepared contains a for update clause */
EXEC SQL prepare x from 'select fname, lname from customer for update';
EXEC SQL declare xc cursor for x; --note no 'for update' clause in declare
1-492
Informix Guide to SQL: Syntax
SELECT
for (;;)
{
EXEC SQL fetch xc into $fname, $lname;
if (strncmp(SQLSTATE, '00', 2) != 0) break;
printf("%d %s %s\n",cnum, fname, lname );
if (cnum == 999)--update rows with 999 customer_num
EXEC SQL update customer set fname = 'rosey' where current of xc;
}
EXEC SQL close xc;
EXEC SQL disconnect current;
A SELECT ... FOR UPDATE statement, like an update cursor, allows you to
perform updates that are not possible with the UPDATE statement alone,
because both the decision to update and the values of the new data items can
be based on the original contents of the row. The UPDATE statement cannot
interrogate the table that is being updated.
Syntax That is Incompatible with the FOR UPDATE Clause
A SELECT statement that uses a FOR UPDATE clause must conform to the
following restrictions:
■
The statement can select data from only one table.
■
The statement cannot include any aggregate functions.
■
The statement cannot include any of the following clauses or
keywords: DISTINCT, FOR READ ONLY, GROUP BY, INTO TEMP,
ORDER BY, UNION, or UNIQUE.
For information on how to declare an update cursor for a SELECT statement
that does not include a FOR UPDATE clause, see page 1-242.
FOR READ ONLY Clause
Use the FOR READ ONLY clause to specify that the select cursor declared for
the SELECT statement is a read-only cursor. A read-only cursor is a cursor that
cannot modify data. This section provides the following information about
the FOR READ ONLY clause:
■
■
When you must use the FOR READ ONLY clause
Syntax restrictions on a SELECT statement that uses a FOR READ
ONLY clause
SQL Statements 1-493
SELECT
Using the FOR READ ONLY Clause in Read-Only Mode
Normally, you do not need to include the FOR READ ONLY clause in a SELECT
statement. A SELECT statement is a read-only operation by definition, so the
FOR READ ONLY clause is usually unnecessary. However, in certain special
circumstances, you must include the FOR READ ONLY clause in a SELECT
statement.
ANSI
If you have used the High-Performance Loader (HPL) in express mode to
load data into the tables of an ANSI-mode database, and you have not yet
performed a level-0 backup of this data, the database is in read-only mode.
When the database is in read-only mode, the database server rejects any
attempts by a select cursor to access the data unless the SELECT or the
DECLARE includes a FOR READ ONLY clause. This restriction remains in effect
until the user has performed a level-0 backup of the data.
When the database is an ANSI-mode database, select cursors are update
cursors by default. An update cursor is a cursor that can be used to modify
data. These update cursors are incompatible with the read-only mode of the
database. For example, the following SELECT statement against the
customer_ansi table fails:
EXEC SQL declare ansi_curs cursor for
select * from customer_ansi;
The solution is to include the FOR READ ONLY clause in your select cursors.
The read-only cursor that this clause specifies is compatible with the readonly mode of the database. For example, the following SELECT FOR READ
ONLY statement against the customer_ansi table succeeds:
EXEC SQL declare ansi_read cursor for
select * from customer_ansi for read only;
♦
D/B
1-494
DB-Access executes all SELECT statements with select cursors. Therefore, you
must include the FOR READ ONLY clause in all SELECT statements that access
data in a read-only ANSI-mode database. The FOR READ ONLY clause causes
DB-Access to declare the cursor for the SELECT statement as a read-only
cursor. ♦
Informix Guide to SQL: Syntax
SELECT
For more information on the express mode of HPL, see the Guide to the
High-Performance Loader. For more information on level-0 backups, see the
INFORMIX-OnLine Dynamic Server Archive and Backup Guide. For more information on select cursors, read-only cursors, and update cursors, see the
DECLARE statement on page 1-234.
Syntax That Is Incompatible with the FOR READ ONLY Clause
Whether your database is an ANSI-mode database or a database that is not
ANSI compliant, you cannot include both the FOR READ ONLY clause and the
FOR UPDATE clause in the same SELECT statement. If you attempt to do so,
the SELECT statement fails.
For information on how to declare a read-only cursor for a SELECT statement
that does not include a FOR READ ONLY clause, see page 1-245.
INTO TEMP Clause
INTO TEMP
Clause
INTO TEMP
temp table name
WITH NO LOG
SQL Statements 1-495
SELECT
Element
Purpose
temp table name The simple name of a temporary
table. This table contains the
results of the SELECT statement.
The column names of the
temporary table are those that
are named in the select list of the
SELECT clause.
Restrictions
Syntax
The name must be different from Identifier, p. 1-723
any existing table, view, or
synonym name in the current
database, but it does not have to
be different from other
temporary table names used by
other users. You must have the
Connect privilege on a database
to create a temporary table in
that database. If you use the
INTO TEMP clause to create a
temporary table, you must
supply a display label for all
expressions in the select list
other than simple column
expressions.
The INTO TEMP clause creates a temporary table that contains the query
results. The initial and next extents for the temporary table are always eight
pages. Temporary tables created with the INTO TEMP clause are explicit
temporary tables. Explicit temporary tables can also be created with the
CREATE TEMP TABLE statement.
If the DBSPACETEMP environment variable is set for INFORMIX-OnLine
Dynamic Server, temporary tables created with the INTO TEMP clause are
located in the dbspaces that are specified in the DBSPACETEMP list. You can
also specify dbspace settings with the ONCONFIG parameter DBSPACETEMP.
If neither the environment variable nor configuration parameter is set, the
default setting is the root dbspace. The settings specified for the
DBSPACETEMP environment variable take precedence over the ONCONFIG
parameter DBSPACETEMP and the default setting. For more information
about creating temporary tables, see the CREATE TABLE statement on page
1-154. For more information about the DBSPACETEMP environment variable,
see Chapter 4 of the Informix Guide to SQL: Reference. For more information
about the ONCONFIG parameter DBSPACETEMP, see the INFORMIX-OnLine
Dynamic Server Administrator’s Guide.
SE
1-496
Temporary tables are located in whatever directory is specified in the
DBTEMP environment variable setting or in the directory of the database
(that is, the *.dbs directory). ♦
Informix Guide to SQL: Syntax
SELECT
The temporary table disappears when your program ends or when you issue
a DROP TABLE statement on the temporary table. If your database does not
have logging, or if it has logging, and you created the temporary table
without the WITH NO LOG keywords, the temporary table disappears when
you close the current database.
If you use the same query results more than once, using a temporary table
saves time. In addition, using an INTO TEMP clause often gives you clearer
and more understandable SELECT statements. However, the data in the
temporary table is static; data is not updated as changes are made to the
tables used to build the temporary table.
The column names of the temporary table are those named in the SELECT
clause. You must supply a display label for all expressions other than simple
column expressions. The display label for a column or expression becomes
the column name in the temporary table. If you do not provide a display label
for a column expression, the temporary table uses the column name from the
select list. The following example creates the pushdate table with two
columns, customer_num and slowdate:
SELECT customer_num, call_dtime + 5 UNITS DAY slowdate
FROM cust_calls INTO TEMP pushdate
You can put indexes on a temporary table.
INTO TEMP Clause and WHERE Clause
When you use the INTO TEMP clause combined with the WHERE clause, and
no rows are returned, the SQLNOTFOUND value is 100 in ANSI-compliant
databases and 0 in databases that are not ANSI compliant. If the SELECT INTO
TEMP ... WHERE ... statement is a part of a multistatement prepare and no
rows are returned, the SQLNOTFOUND value is 100 for both ANSI-compliant
databases and databases that are not ANSI-compliant.
SQL Statements 1-497
SELECT
INTO TEMP Clause and INTO
ESQL
Do not use the INTO option with the INTO TEMP clause: If you do, no results
are returned to the program variables and the sqlcode variable is set to a
negative value. The name of the sqlcode variable for each product is shown
in the following table.
Product
Variable Name
ESQL/C
sqlca.sqlcode, SQLCODE
ESQL/COBOL
SQLCODE OF SQLCA
♦
WITH NO LOG Option
If you use the WITH NO LOG keywords, operations on the temporary table are
not included in the transaction-log operations. You can use this option to
reduce the overhead of transaction logging.
UNION Operator
Place the UNION operator between two SELECT statements to combine the
queries into a single query. You can string several SELECT statements
together using the UNION operator. Corresponding items do not need to
have the same name.
Restrictions on a Combined SELECT
Several restrictions apply on the queries that you can connect with a UNION
operator, as the following list describes:
1-498
■
The number of items in the SELECT clause of each query must be the
same, and the corresponding items in each SELECT clause must have
compatible data types.
■
If you use an ORDER BY clause, it must follow the last SELECT clause,
and you must refer to the item ordered by integer, not by identifier.
Ordering takes place after the set operation is complete.
Informix Guide to SQL: Syntax
SELECT
ESQL
■
You cannot use a UNION operator inside a subquery or in the
definition of a view.
■
You cannot use an INTO clause in a query unless you are sure that the
compound query returns exactly one row, and you are not using a
cursor. In this case, the INTO clause must be in the first SELECT
statement. ♦
To put the results of a UNION operator into a temporary table, use an INTO
TEMP clause in the final SELECT statement.
Duplicate Rows in a Combined SELECT
If you use the UNION operator alone, the duplicate rows are removed from
the complete set of rows. That is, if multiple rows contain identical values in
each column, only one row is retained. If you use the UNION ALL operator,
all the selected rows are returned (the duplicates are not removed). The
following example uses the UNION ALL operator to join two SELECT
statements without removing duplicates. The query returns a list of all the
calls that were received during the first quarter of 1993 and the first quarter
of 1994.
SELECT customer_num, call_code FROM cust_calls
WHERE call_dtime BETWEEN
DATETIME (1993-1-1) YEAR TO DAY
AND DATETIME (1993-3-31) YEAR TO DAY
UNION ALL
SELECT customer_num, call_code FROM cust_calls
WHERE call_dtime BETWEEN
DATETIME (1994-1-1)YEAR TO DAY
AND DATETIME (1994-3-31) YEAR TO DAY
If you want to remove duplicates, use the UNION operator without the
keyword ALL in the query. In the preceding example, if the combination 101
B were returned in both SELECT statements, a UNION operator would cause
the combination to be listed once. (If you want to remove duplicates within
each SELECT statement, use the DISTINCT keyword in the SELECT clause, as
described on page 1-461.)
SQL Statements 1-499
SELECT
References
In the Informix Guide to SQL: Tutorial, see the discussion of the SELECT
statement in Chapter 2 and Chapter 3.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
SELECT statement.
1-500
Informix Guide to SQL: Syntax
SET
SET
The SET statement allows you to change the object mode of the following
database objects: constraints, indexes, and triggers. You can also use the SET
statement to specify the transaction mode of constraints.
Syntax
+
Table-Mode
Format
p. 1-503
SET
OL
List-Mode
Format
p. 1-508
TransactionMode Format
p. 1-523
Usage
The SET statement has the following purposes:
■
To change the object mode of constraints, indexes, and triggers
When you change the object mode of constraints, indexes, or
triggers, the change is permanent. The setting that the SET statement
produces remains in effect until you change the object mode of the
object again.
■
To set the transaction mode of constraints by specifying whether
constraints are checked at the statement level or at the transaction
level
When you set the transaction mode of constraints, the effect of the
SET statement is limited to the transaction in which it is executed.
The setting that the SET statement produces is effective only during
the transaction. For further information on setting the transaction
mode for constraints, see “Transaction-Mode Format” on page 1-523.
SQL Statements 1-501
SET
Terminology for Object Modes
The SET statement operates on database objects by changing the object mode
of those objects. The terms database objects and objects have a restricted
meaning in the context of the SET statement. Both terms refer to the
constraints, indexes, and triggers in a database.
Similarly, the term object modes has a restricted meaning in the context of the
SET statement. The term refers to the three states that a database object can
have: enabled, disabled, and filtering. The sysobjstate system catalog table
lists all of the objects in the database and the current object mode of each
object.
Do not confuse the terms objects and object modes as used in the SET statement
with the term objects in INFORMIX-NewEra. In the context of
INFORMIX-NewEra, objects refers to objects within an application.
Methods for Changing Object Modes
The SET statement provides the following formats for changing object modes:
table mode and list mode. For an explanation of the table-mode format, see
“Table-Mode Format” on page 1-503. For an explanation of the list-mode
format, see “List-Mode Format” on page 1-508.
Privileges Required for Changing Object Modes
To change the object mode of a constraint, index, or trigger, you must have
the necessary privileges. Specifically, you must meet one of the following
requirements:
1-502
■
You must have the DBA privilege on the database.
■
You must be the owner of the table on which the object is defined and
must have the Resource privilege on the database.
■
You must have the Alter privilege on the table on which the object is
defined and the Resource privilege on the database.
Informix Guide to SQL: Syntax
SET
Table-Mode Format
Table-Mode Format
,
CONSTRAINTS
INDEXES
TRIGGERS
Element
table name
Purpose
The name of the table whose
objects will have their object
mode changed. There is no
default value.
FOR
table name
Object Modes for
Constraints and
Unique Indexes
p. 1-504
Object Modes for
Triggers and
Duplicate Indexes
p. 1-507
Restrictions
Syntax
The table must be a local table. Identifier, p. 1-723
You cannot set the object modes
of objects defined on a
temporary table to the disabled
or filtering modes. For information on the privileges
required to change the object
mode of the objects defined on a
table, see “Privileges Required
for Changing Object Modes” on
page 1-502.
Use the table-mode format to change the object mode of all objects of a given
type that have been defined on a particular table. For example, to change the
object mode of all constraints that are defined on the cust_subset table to the
disabled mode, enter the following statement:
SET CONSTRAINTS FOR cust_subset DISABLED
By using the table-mode format, you can change the object modes of more
than one object type with a single SET statement. For example, to change the
object mode of all constraints, indexes, and triggers that are defined on the
cust_subset table to the enabled mode, enter the following statement:
SET CONSTRAINTS, INDEXES, TRIGGERS FOR cust_subset
ENABLED
SQL Statements 1-503
SET
Object Modes for Constraints and Unique Indexes
Object Modes for Constraints
and Unique Indexes
DISABLED
ENABLED
FILTERING
WITHOUT
ERROR
WITH
ERROR
You can specify the disabled, enabled, or filtering object modes for a
constraint or a unique index. You must specify one of these object modes in
your SET statement. The SET statement has no default object mode.
You can also specify the object mode for a constraint when you create the
constraint with the ALTER TABLE or CREATE TABLE statements. If you do not
specify the object mode for a constraint in one of these statements or in a SET
statement, the constraint is in the enabled object mode by default.
You can also specify the object mode for a unique index when you create the
index with the CREATE INDEX statement. If you do not specify the object
mode for a unique index in the CREATE INDEX statement or in a SET
statement, the unique index is in the enabled object mode by default.
For definitions of the disabled, enabled, and filtering object modes see “Using
Object Modes with Data Manipulation Statements” on page 1-509. For an
explanation of the benefits of these object modes, see “Benefits of Object
Modes” on page 1-521.
Error Options for Filtering Mode
When you change the object mode of a constraint or unique index to the
filtering mode, you can specify the following error options: WITHOUT ERROR
or WITH ERROR.
1-504
Informix Guide to SQL: Syntax
SET
The WITHOUT ERROR Option
The WITHOUT ERROR option signifies that when the database server executes
an INSERT, DELETE, or UPDATE statement, and one or more of the target rows
causes a constraint violation or unique-index violation, no integrity-violation
error message is returned to the user. The WITHOUT ERROR option is the
default error option.
The WITH ERROR Option
The WITH ERROR option signifies that when the database server executes an
INSERT, DELETE, or UPDATE statement, and one or more of the target rows
causes a constraint violation or unique-index violation, an integrity-violation
error message is returned to the user.
Scope of Error Options
The WITH ERROR and WITHOUT ERROR options apply only when the
database server executes an INSERT, DELETE, or UPDATE statement, and one
or more of the target rows causes a constraint violation or unique index
violation. These error options control whether the database server displays
an integrity-violation error message after it executes these statements.
These error options do not apply when you attempt to change the object
mode of a disabled constraint or disabled unique index to the enabled or
filtering mode, and the SET statement fails because one or more rows in the
target table violates the constraint or the unique-index requirement. In these
cases, if a violations table has been started for the table that contains the
inconsistent data, the database server returns an integrity-violation error
message regardless of the error option that is specified in the SET statement.
Violations and Diagnostics Tables for Filtering Mode
When you specify the filtering mode for constraints or unique indexes in a
SET statement, violations and diagnostics tables are not automatically started
for the target table. When you set objects to the filtering mode, be sure to start
the violations and diagnostics tables for the target table on which the filtering
mode objects are defined. The violations table captures rows that fail to meet
integrity requirements. The diagnostics table captures information about
each row that fails to meet integrity requirements.
SQL Statements 1-505
SET
When to Start the Violations and Diagnostics Tables
You are not required to start the violations and diagnostics tables before you
set objects to the filtering mode. If you have not started a violations and
diagnostics table when you set an object to the filtering mode, the database
server executes your SET statement and does not return an error. Similarly, if
you issue an INSERT, DELETE, or UPDATE statement on the target table, and
you have not started a violations and diagnostics table for the target table, the
database server executes the statement and does not return an error as long
as all of the integrity requirements on the table are satisfied.
If you have not started a violations and diagnostics table for the target table
with filtering-mode objects, the database server does not return an error until
an INSERT, DELETE, or UPDATE statement fails to satisfy an integrity
requirement on the table. If an INSERT, DELETE, or UPDATE statement fails to
satisfy the constraint or unique-index requirement for a particular row, the
database server cannot filter the bad row to the violations table because no
violations table is associated with the target table. The user receives an error
message indicating that no violations table has been started for the target
table.
To prevent such errors, start the violations and diagnostics tables for the
target table at one of the following points:
■
You can start the violations and diagnostics tables before you set any
objects that are defined on the table to the filtering mode.
■
You can start the violations and diagnostics tables after you set
objects to the filtering mode but before any users issue INSERT,
DELETE, or UPDATE statements that could violate any integrity
requirements on the target table.
How to Start the Violations and Diagnostics Tables
To create the violations and diagnostics tables and associate them with the
target table, use the START VIOLATIONS TABLE statement. In this statement,
specify the name of the target table for which the violations and diagnostics
tables are to be started. You can also assign names to the violations and
diagnostics tables in this statement.
For further information on the START VIOLATIONS TABLE statement and the
structure of the violations and diagnostics tables themselves, see the START
VIOLATIONS TABLE statement on page 1-584.
1-506
Informix Guide to SQL: Syntax
SET
How to Stop the Violations and Diagnostics Tables
After you turn off filtering mode for the objects that are defined on a target
table, and you no longer need the violations and diagnostics tables, use the
STOP VIOLATIONS TABLE statement to drop the association between the
target table and the violations and diagnostics tables. In this statement, you
specify the name of the target table whose association with the violations and
diagnostics tables is to be dropped.
For further information on using the STOP VIOLATIONS TABLE statement, see
the STOP VIOLATIONS TABLE statement on page 1-603.
Object Modes for Triggers and Duplicate Indexes
Object Modes for Triggers
and Duplicate Indexes
DISABLED
ENABLED
You can specify the disabled or enabled object modes for triggers or duplicate
indexes. You must specify one of these object modes in your SET statement.
The SET statement has no default object mode.
You can also specify the object mode for a trigger when you create the trigger
with the CREATE TRIGGER statement. If you do not specify the object mode
for a trigger in the CREATE TRIGGER statement or in a SET statement, the
trigger is in the enabled object mode by default.
You can also specify the object mode for a duplicate index when you create
the index with the CREATE INDEX statement. If you do not specify the object
mode for a duplicate index in the CREATE INDEX statement or in a SET
statement, the duplicate index is in the enabled object mode by default.
For definitions of the disabled and enabled object modes, see “Using Object
Modes with Data Manipulation Statements” on page 1-509. For an explanation of the benefits of these two object modes, see “Benefits of Object
Modes” on page 1-521.
SQL Statements 1-507
SET
List-Mode Format
List-Mode Format
,
CONSTRAINTS
constraint
name
,
INDEXES
index name
Object Modes for
Constraints and
Unique Indexes
p. 1-504
Object Modes for
Constraints and
Unique Indexes
p. 1-504
Object Modes for
Triggers and
Duplicate Indexes
p. 1-507
,
TRIGGERS
trigger name
Element
Purpose
constraint name The name of the constraint
whose object mode is to be set, or
a list of constraint names. There
is no default value.
index name
The name of the index whose
object mode is to be set, or a list
of index names. There is no
default value.
trigger name
The name of the trigger whose
object mode is to be set, or a list
of trigger names. There is no
default value.
Object Modes for
Triggers and
Duplicate Indexes
p. 1-507
Restrictions
Each constraint in the list must
be a local constraint. All
constraints in the list must be
defined on the same table.
Each index in the list must be a
local index. All indexes in the list
must be defined on the same
table.
Each trigger in the list must be a
local trigger. All triggers in the
list must be defined on the same
table.
Syntax
Identifier, p. 1-723
Identifier, p. 1-723
Identifier, p. 1-723
Use the list-mode format to change the object mode for a particular
constraint, index, or trigger. For example, to change the object mode of the
unique index unq_ssn on the cust_subset table to filtering mode, enter the
following statement:
SET INDEXES unq_ssn FILTERING
1-508
Informix Guide to SQL: Syntax
SET
You can also use the list-mode format to change the object mode for a list of
constraints, indexes, or triggers that are defined on the same table. Assume
that four triggers are defined on the cust_subset table: insert_trig,
update_trig, delete_trig, and execute_trig. Also assume that all four triggers
are in the enabled mode. To change the object mode of all the triggers except
execute_trig to the disabled mode, enter the following statement:
SET TRIGGERS insert_trig, update_trig, delete_trig DISABLED
Using Object Modes with Data Manipulation Statements
You can use object modes to control the effects of INSERT, DELETE, and
UPDATE statements. Your choice of object modes affects the tables whose
data you are manipulating, the behavior of the objects defined on those
tables, and the behavior of the data manipulation statements themselves.
What do we mean by the terms enabled, disabled, and filtering? Definitions of
these object modes follow. These definitions explain how each object mode
affects tables and data manipulation statements. The definitions focus on the
object modes of constraints as an illustration, but the same principles apply
to indexes and triggers as well.
Definition of Enabled Mode
Constraints, indexes, and triggers are in the enabled mode by default. When
an object is in the enabled mode, the database server recognizes the existence
of the object and takes the object into consideration while it executes data
manipulation statements. For example, when a constraint is enabled, any
INSERT, UPDATE, or DELETE statement that violates the constraint fails, and
the target row remains unchanged. In addition, the user receives an error
message.
Definition of Disabled Mode
When an object is in the disabled mode, the database server acts as if the
object did not exist and does not take it into consideration during the
execution of data manipulation statements. For example, when a constraint
is disabled, any INSERT, UPDATE, or DELETE statement that violates the
constraint succeeds, and the target row is changed. The user does not receive
an error message.
SQL Statements 1-509
SET
Definition of Filtering Mode
When an object is in the filtering mode, the object behaves the same as in the
enabled mode in that the database server recognizes the existence of the
object during INSERT, UPDATE, and DELETE statements. For example, when
a constraint is in the filtering mode, and an INSERT, DELETE, or UPDATE
statement is executed, any target rows that violate the constraint remain
unchanged.
However, the database server handles data manipulation statements differently for objects in enabled and filtering mode, as the following paragraphs
describe:
■
If a constraint or unique index is in the enabled mode, the database
server carries out the INSERT, UPDATE, or DELETE statement only if
all the target rows affected by the statement satisfy the constraint or
the unique index requirement. The database server updates all the
target rows in the table.
■
If a constraint or unique index is in the filtering mode, the database
server carries out the INSERT, UPDATE, or DELETE statement even if
one or more of the target rows fail to satisfy the constraint or the
unique index requirement. The database server updates the good
rows in the table (the target rows that satisfy the constraint or unique
index requirement). The database server does not update the bad
rows in the table (that is, the target rows that fail to satisfy the
constraint or unique index requirement). Instead the database server
sends each bad row to a special table called the violations table. The
database server places information about the nature of the violation
for each bad row in another special table called the diagnostics table.
Example of Object Modes with Data Manipulation
Statements
An example with the INSERT statement can illustrate the differences between
the enabled, disabled, and filtering modes. Consider an INSERT statement in
which a user tries to add a row that does not satisfy an integrity constraint on
a table. For example, assume that a user joe has created a table named
cust_subset, and this table consists of the following columns: ssn (customer’s
social security number), fname (customer’s first name), lname (customer’s
last name), and city (city in which the customer lives). The ssn column has
the INT data type. The other three columns have the CHAR data type.
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Informix Guide to SQL: Syntax
SET
Assume that user joe has defined the lname column as not null but has not
assigned a name to the not null constraint, so the database server has
implicitly assigned the name n104_7 to this constraint. Finally, assume that
user joe has created a unique index named unq_ssn on the ssn column.
Now a user linda who has the Insert privilege on the cust_subset table enters
the following INSERT statement on this table:
INSERT INTO cust_subset (ssn, fname, city)
VALUES (973824499, "jane", "los altos")
User linda has entered values for all the columns of the new row except for
the lname column, even though the lname column has been defined as a not
null column. The database server behaves in the following ways, depending
on the object mode of the constraint:
■
If the constraint is disabled, the row is inserted in the target table, and
no error is returned to the user.
■
If the constraint is enabled, the row is not inserted in the target table.
A constraint-violation error is returned to the user, and the effects of
the statement are rolled back (if the database is an OnLine database
with logging).
■
If the constraint is filtering, the row is not inserted in the target table.
Instead the row is inserted in the violations table. Information about
the integrity violation caused by the row is placed in the diagnostics
table. The effects of the INSERT statement are not rolled back. You
receive an error message if you specified the WITH ERROR option for
the filtering-mode constraint. By analyzing the contents of the violations and the diagnostics tables, you can identify the reason for the
failure and either take corrective action or roll back the operation.
We can better grasp the distinctions among disabled, enabled, and filtering
modes by viewing the actual results of the INSERT statement shown in the
preceding example.
SQL Statements 1-511
SET
Results of the Insert Operation When the Constraint Is Disabled
If the not null constraint on the cust_subset table is disabled, the INSERT
statement that user linda issues successfully inserts the new row in this table.
The new row of the cust_subset table has the following column values.
ssn
fname
lname
city
973824499
jane
NULL
los altos
Results of the Insert Operation When the Constraint Is Enabled
If the not null constraint on the cust_subset table is enabled, the INSERT
statement fails to insert the new row in this table. Instead user linda receives
the following error message when she enters the INSERT statement:
-292 An implied insert column lname does not accept NULLs.
Results of the Insert When Constraint Is in Filtering Mode
If the not null constraint on the cust_subset table is set to the filtering mode,
the INSERT statement that user linda issues fails to insert the new row in this
table. Instead the new row is inserted into the violations table, and a
diagnostic row that describes the integrity violation is added to the
diagnostics table.
Assume that user joe has started a violations and diagnostics table for the
cust_subset table. The violations table is named cust_subset_vio, and the
diagnostics table is named cust_subset_dia. The new row added to the
cust_subset_vio violations table when user linda issues the INSERT
statement on the cust_subset target table has the following column values.
ssn
fname
lname
city
informix_tupleid informix_optype informix_recowner
973824499
jane
NULL
los altos
1
1-512
Informix Guide to SQL: Syntax
I
linda
SET
This new row in the cust_subset_vio violations table has the following
characteristics:
■
The first four columns of the violations table exactly match the
columns of the target table. These four columns have the same names
and the same data types as the corresponding columns of the target
table, and they have the column values that were supplied by the
INSERT statement that user linda entered.
■
The value 1 in the informix_tupleid column is a unique serial
identifier that is assigned to the nonconforming row.
■
The value I in the informix_optype column is a code that identifies
the type of operation that has caused this nonconforming row to be
created. Specifically, I stands for an insert operation.
■
The value linda in the informix_recowner column identifies the
user who issued the statement that caused this nonconforming row
to be created.
The INSERT statement that user linda issued on the cust_subset target table
also causes a diagnostic row to be added to the cust_subset_dia diagnostics
table. The new diagnostic row added to the diagnostics table has the
following column values.
informix_tupleid
objtype
objowner
objname
1
C
joe
n104_7
This new diagnostic row in the cust_subset_dia diagnostics table has the
following characteristics:
■
This row of the diagnostics table is linked to the corresponding row
of the violations table by means of the informix_tupleid column that
appears in both tables. The value 1 appears in this column in both
tables.
■
The value C in the objtype column identifies the type of integrity
violation that the corresponding row in the violations table caused.
Specifically, the value C stands for a constraint violation.
SQL Statements 1-513
SET
■
The value joe in the objowner column identifies the owner of the
constraint for which an integrity violation was detected.
■
The value n104_7 in the objname column gives the name of the
constraint for which an integrity violation was detected.
By joining the violations and diagnostics tables, user joe (who owns the
cust_subset target table and its associated special tables) or the DBA can find
out that the row in the violations table whose informix_tupleid value is 1
was created after an INSERT statement and that this row is violating a
constraint. The table owner or DBA can query the sysconstraints system
catalog table to determine that this constraint is a not null constraint. Now
that the reason for the failure of the INSERT statement is known, user joe or
the DBA can take corrective action.
Multiple Diagnostic Rows for One Violations Row
In the preceding example, only one row in the diagnostics table corresponds
to the new row in the violations table. However, more than one diagnostic
row can be added to the diagnostics table when a single new row is added to
the violations table. For example, if the ssn value (973824499) that user linda
entered in the INSERT statement had been the same as an existing value in the
ssn column of the cust_subset target table, only one new row would appear
in the violations table, but the following two diagnostic rows would be
present in the cust_subset_dia diagnostics table.
informix_tupleid
objtype
objowner
objname
1
C
joe
n104_7
1
I
joe
unq_ssn
Both rows in the diagnostics table correspond to the same row of the
violations table because both of these rows have the value 1 in the
informix_tupleid column. However, the first diagnostic row identifies the
constraint violation caused by the INSERT statement that user linda issued,
while the second diagnostic row identifies the unique-index violation caused
by the same INSERT statement. In this second diagnostic row, the value I in
the objtype column stands for a unique-index violation, and the value
unq_ssn in the objname column gives the name of the index for which the
integrity violation was detected.
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Informix Guide to SQL: Syntax
SET
For information on when and how to start violations and diagnostics tables
for a target table, see “Violations and Diagnostics Tables for Filtering Mode”
on page 1-505. For further information on the structure of the violations and
diagnostics tables, see the START VIOLATIONS TABLE statement on
page 1-584.
Using Object Modes to Achieve Data Integrity
In addition to using object modes with data manipulation statements, you
can also use object modes when you add a new constraint or new unique
index to a target table. By selecting the correct object mode, you can add the
constraint or index to the target table easily even if existing rows in the target
table violate the new integrity specification.
You can add a new constraint or index easily by taking the following steps. If
you follow this procedure, you do not have to examine the entire target table
to identify rows that fail to satisfy the constraint or unique-index
requirement:
■
Add the constraint or index in the enabled mode. If all existing rows
in the table satisfy the constraint or unique-index requirement, your
ALTER TABLE or CREATE INDEX statement executes successfully, and
you do not need to take any further steps. However, if any existing
rows in the table fail to satisfy the constraint or unique-index
requirement, your ALTER TABLE or CREATE INDEX statement returns
an error message, and you need to take the following steps.
■
Add the constraint or index in the disabled mode. Issue the ALTER
TABLE statement again, and specify the DISABLED keyword in the
ADD CONSTRAINT or MODIFY clause; or issue the CREATE INDEX
statement again, and specify the DISABLED keyword.
■
Start a violations and diagnostics table for the target table with the
START VIOLATIONS TABLE statement.
■
Issue a SET statement to switch the object mode of the constraint or
index to the enabled mode. When you issue this statement, the
statement fails, and existing rows in the target table that violate the
constraint or the unique-index requirement are duplicated in the
violations table. The constraint or index remains disabled, and you
receive an integrity-violation error message.
SQL Statements 1-515
SET
■
Issue a SELECT statement on the violations table to retrieve the
nonconforming rows that were duplicated from the target table. You
might need to join the violations and diagnostics tables to get all the
necessary information.
■
Take corrective action on the rows in the target table that violate the
constraint.
■
After you fix all the nonconforming rows in the target table, issue the
SET statement again to switch the disabled constraint or index to the
enabled mode. This time the constraint or index is enabled, and no
integrity-violation error message is returned because all rows in the
target table now satisfy the new constraint or unique-index
requirement.
Example of Using Object Modes to Achieve Data Integrity
The following example shows how to use object modes to add a constraint
and unique index to a target table easily. Assume that a user joe has created
a table named cust_subset, and this table consists of the following columns:
ssn (customer’s social security number), fname (customer’s first name),
lname (customer’s last name), and city (city in which the customer lives).
Also assume that no constraints or unique indexes are defined on the
cust_subset table and that the fname column is the primary key. In addition,
assume that no violations and diagnostics tables currently exist for this target
table. Finally, assume that this table currently contains four rows with the
following column values.
1-516
ssn
fname
lname
city
111763227
mark
jackson
sunnyvale
222781244
rhonda
NULL
palo alto
111763227
steve
NULL
san mateo
333992276
tammy
jones
san jose
Informix Guide to SQL: Syntax
SET
Adding the Objects in the Enabled Mode
User joe, the owner of the cust_subset table, enters the following statements
to add a unique index on the ssn column and a not null constraint on the
lname column:
CREATE UNIQUE INDEX unq_ssn ON cust_subset (ssn) ENABLED;
ALTER TABLE cust_subset MODIFY (lname CHAR(15)
NOT NULL CONSTRAINT lname_notblank ENABLED);
Both of these statements fail because existing rows in the cust_subset table
violate the integrity specifications. The row whose fname value is rhonda
violates the not null constraint on the lname column. The row whose fname
value is steve violates both the not null constraint on the lname column and
the unique-index requirement on the ssn column.
Adding the Objects in the Disabled Mode
To recover from the preceding errors, user joe reenters the CREATE INDEX
and ALTER TABLE statements and specifies the disabled mode in both statements, as follows:
CREATE UNIQUE INDEX unq_ssn ON cust_subset (ssn) DISABLED;
ALTER TABLE cust_subset MODIFY (lname CHAR(15)
NOT NULL CONSTRAINT lname_notblank DISABLED);
Both of these statements execute successfully because the database server
does not enforce unique-index requirements or constraint specifications
when these objects are disabled.
Starting a Violations and Diagnostics Table
Now that the new constraint and index are added for the cust_subset table,
user joe takes steps to find out which existing rows in the cust_subset table
violate the constraint and the index.
First, user joe enters the following statement to start a violations and
diagnostics table for the cust_subset table:
START VIOLATIONS TABLE FOR cust_subset
Because user joe has not assigned names to the violations and diagnostics
tables in this statement, the tables are named cust_subset_vio and
cust_subset_dia by default.
SQL Statements 1-517
SET
Using the SET Statement to Capture Violations
Now that violations and diagnostics tables exist for the target table, user joe
issues the following SET statement to switch the mode of the new index and
constraint from the disabled mode to the enabled mode:
SET CONSTRAINTS, INDEXES FOR cust_subset ENABLED
The result of this SET statement is that the existing rows in the cust_subset
table that violate the constraint and the unique-index requirement are copied
to the cust_subset_vio violations table, and diagnostic information about the
nonconforming rows is added to the cust_subset_dia diagnostics table. The
SET statement fails, and the constraint and index remain disabled.
The following table shows the contents of the cust_subset_vio violations
table after user joe issues the SET statement.
ssn
fname
lname
city
informix_tupleid
informix_optype
informix_recowner
222781244 rhonda
NULL
palo alto
1
S
joe
111763227
NULL
san mateo 2
S
joe
steve
These two rows in the cust_subset_vio violations table have the following
characteristics:
1-518
■
The row in the cust_subset target table whose fname value is rhonda
is duplicated to the cust_subset_vio violations table because this
row violates the not null constraint on the lname column.
■
The row in the cust_subset target table whose fname value is steve
is duplicated to the cust_subset_vio violations table because this
row violates the not null constraint on the lname column and the
unique-index requirement on the ssn column.
■
The value 1 in the informix_tupleid column for the first row and the
value 2 in the informix_tupleid column for the second row are
unique serial identifiers assigned to the nonconforming rows.
Informix Guide to SQL: Syntax
SET
■
The value S in the informix_optype column for each row is a code
that identifies the type of operation that has caused this nonconforming row to be placed in the violations table. Specifically, the S
stands for a SET statement.
■
The value joe in the informix_recowner column for each row
identifies the user who issued the statement that caused this nonconforming row to be placed in the violations table.
The following table shows contents of the cust_subset_dia diagnostics table
after user joe issues the SET statement.
informix_tupleid
objtype
objowner
objname
1
C
joe
lname_notblank
2
C
joe
lname_notblank
2
I
joe
unq_ssn
These three rows in the cust_subset_dia diagnostics table have the following
characteristics:
■
Each row in the diagnostics table and the corresponding row in the
violations table are joined by the informix_tupleid column that
appears in both tables.
■
The first row in the diagnostics table has an informix_tupleid value
of 1. It is joined to the row in the violations table whose
informix_tupleid value is 1. The value C in the objtype column for
this diagnostic row identifies the type of integrity violation that was
caused by the corresponding row in the violations table. Specifically,
the value C stands for a constraint violation. The value
lname_notblank in the objname column for this diagnostic row
gives the name of the constraint for which an integrity violation was
detected.
SQL Statements 1-519
SET
■
The second row in the diagnostics table has an informix_tupleid
value of 2. It is joined to the row in the violations table whose
informix_tupleid value is 2. The value C in the objtype column for
this second diagnostic row indicates that a constraint violation was
caused by the corresponding row in the violations table. The value
lname_notblank in the objname column for this diagnostic row
gives the name of the constraint for which an integrity violation was
detected.
■
The third row in the diagnostics table has an informix_tupleid value
of 2. It is also joined to the row in the violations table whose
informix_tupleid value is 2. The value I in the objtype column for
this third diagnostic row indicates that a unique-index violation was
caused by the corresponding row in the violations table. The value
unq_ssn in the objname column for this diagnostic row gives the
name of the index for which an integrity violation was detected.
■
The value joe in the objowner column of all three diagnostic rows
identifies the owner of the object for which an integrity violation was
detected. The name of user joe appears in all three rows because he
created the constraint and index on the cust_subset table.
Identifying Nonconforming Rows to Obtain Information
To determine the contents of the violations table, user joe enters a SELECT
statement to retrieve all rows from the table. Then, to obtain complete
diagnostic information about the nonconforming rows, user joe joins the
violations and diagnostics tables by means of another SELECT statement.
User joe can perform these operations either interactively or through a
program.
Taking Corrective Action on the Nonconforming Rows
After the user joe identifies the nonconforming rows in the cust_subset table,
he can correct them. For example, he can enter UPDATE statements on the
cust_subset table either interactively or through a program.
1-520
Informix Guide to SQL: Syntax
SET
Enabling the Disabled Objects
Once all the nonconforming rows in the cust_subset table are corrected, user
joe issues the following SET statement to set the new constraint and index to
the enabled mode:
SET CONSTRAINTS, INDEXES FOR cust_subset ENABLED
This time the SET statement executes successfully. The new constraint and
new unique index are enabled, and no error message is returned to user joe
because all rows in the cust_subset table now satisfy the new constraint
specification and unique-index requirement.
Benefits of Object Modes
The preceding examples show how object modes work when users execute
data manipulation statements on target tables or add new constraints and
indexes to target tables. The preceding examples suggest some of the benefits
of the different object modes. The following sections state these benefits
explicitly.
Benefits of Disabled Mode
The benefits of the disabled mode are as follows:
■
You can use the disabled mode to insert many rows quickly into a
target table. Especially during load operations, updates of the
existing indexes and enforcement of referential constraints make up
a big part of the total cost of the operation. By disabling the indexes
and referential constraints during the load operation, you improve
the performance and efficiency of the load.
SQL Statements 1-521
SET
■
To add a new constraint or new unique index to an existing table, you
can add the object even if some rows in the table do not satisfy the
new integrity specification. If the constraint or index is added to the
table in disabled mode, your ALTER TABLE or CREATE INDEX
statement does not fail no matter how many existing rows violate the
new integrity requirement.
If a violations table has been started, a SET statement that switches
the disabled objects to the enabled or filtering mode fails, but it
causes the nonconforming rows in the target table to be duplicated
in the violations table so that you can identify the rows and take
corrective action. After you fix the nonconforming rows in the target
table, you can reissue the SET statement to switch the disabled objects
to the enabled or filtering mode.
Benefits of Enabled Mode
The enabled mode is the default object mode for all database objects. We can
summarize the benefits of this mode for each type of database object as
follows:
1-522
■
The benefit of enabled mode for constraints is that the database
server enforces the constraint and thus ensures the consistency of the
data in the database.
■
The benefit of enabled mode for indexes is that the database server
updates the index after insert, delete, and update operations. Thus
the index is up to date and is used by the optimizer during database
queries.
■
The benefit of enabled mode for triggers is that the trigger event
always sets the triggered action in motion. Thus the purpose of the
trigger is always realized during actual data-manipulation
operations.
Informix Guide to SQL: Syntax
SET
Benefits of Filtering Mode
The benefits of setting a constraint or unique index to the filtering mode are
as follows:
■
During load operations, inserts that violate a filtering mode
constraint or unique index do not cause the load operation to fail.
Instead, the database server filters the bad rows to the violations
table and continues the load operation.
■
When an INSERT, DELETE, or UPDATE statement that affects multiple
rows causes a filtering mode constraint or unique index to be
violated for a particular row or rows, the statement does not fail.
Instead, the database server filters the bad row or rows to the violations table and continues to execute the statement.
■
When any INSERT, DELETE, or UPDATE statement violates a filtering
mode constraint or unique index, the user can identify the failed row
or rows and take corrective action. The violations and diagnostics
tables capture the necessary information, and users can take
corrective action after they analyze this information.
Transaction-Mode Format
Transaction-Mode Format
CONSTRAINTS
,
constraint
name
IMMEDIATE
ALL
DEFERRED
Element
Purpose
constraint name The name of the constraint
whose transaction mode is to be
changed, or a list of constraint
names. There is no default value.
Restrictions
Syntax
The specified constraint must
Identifier, p. 1-723
exist in an OnLine database with
logging. You cannot change the
transaction mode of a constraint
to deferred mode unless the
constraint is currently in the
enabled mode. All constraints in
a list of constraints must exist in
the same database.
SQL Statements 1-523
SET
You can use the transaction-mode format of the SET statement to set the
transaction mode of constraints.
You use the IMMEDIATE keyword to set the transaction mode of constraints
to statement-level checking. You use the DEFERRED keyword to set the transaction mode to transaction-level checking.
You can set the transaction mode of constraints only in an OnLine database
with logging.
Statement-Level Checking
When you set the transaction mode to immediate, statement-level checking
is turned on, and all specified constraints are checked at the end of each
INSERT, UPDATE, or DELETE statement. If a constraint violation occurs, the
statement is not executed. Immediate is the default transaction mode of
constraints.
Transaction-Level Checking
When you set the transaction mode of constraints to deferred, statementlevel checking is turned off, and all specified constraints are not checked until
the transaction is committed. If a constraint violation occurs while the
transaction is being committed, the transaction is rolled back.
Tip: If you defer checking a primary-key constraint, the checking of the not null
constraint for that column or set of columns is also deferred.
Duration of Transaction Modes
The duration of the transaction mode that the SET statement specifies is the
transaction in which the SET statement is executed. You cannot execute this
form of the SET statement outside a transaction. Once a COMMIT WORK or
ROLLBACK WORK statement is successfully completed, the transaction mode
of all constraints reverts to IMMEDIATE.
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Informix Guide to SQL: Syntax
SET
Switching Transaction Modes
To switch from transaction-level checking to statement-level checking, you
can use the SET statement to set the transaction mode to immediate, or you
can use a COMMIT WORK or ROLLBACK WORK statement in your transaction.
Specifying All Constraints or a List of Constraints
You can specify all constraints in the database in your SET statement, or you
can specify a single constraint or list of constraints.
Specifying All Constraints
If you specify the ALL keyword, the SET statement sets the transaction mode
for all constraints in the database. If any statement in the transaction requires
that any constraint on any table in the database be checked, the database
server performs the checks at the statement level or the transaction level,
depending on the setting that you specify in the SET statement.
Specifying a List of Constraints
If you specify a single constraint name or a list of constraints, the SET
statement sets the transaction mode for the specified constraints only. If any
statement in the transaction requires checking of a constraint that you did not
specify in the SET statement, that constraint is checked at the statement level
regardless of the setting that you specified in the SET statement for other
constraints.
When you specify a list of constraints, the constraints do not have to be
defined on the same table, but they must exist in the same database.
Specifying Remote Constraints
You can set the transaction mode of local constraints or remote constraints.
That is, the constraints that are specified in the transaction-mode form of the
SET statement can be constraints that are defined on local tables or constraints
that are defined on remote tables.
SQL Statements 1-525
SET
Examples of Setting the Transaction Mode for Constraints
The following example shows how to defer checking constraints within a
transaction until the transaction is complete. The SET CONSTRAINTS
statement in the example specifies that any constraints on any tables in the
database are not checked until the COMMIT WORK statement is encountered.
BEGIN WORK
SET CONSTRAINTS ALL DEFERRED
.
.
.
COMMIT WORK
The following example specifies that a list of constraints is not checked until
the transaction is complete:
BEGIN WORK
SET CONSTRAINTS update_const, insert_const DEFERRED
.
.
.
COMMIT WORK
References
See the START VIOLATIONS TABLE and STOP VIOLATIONS TABLE statements
in this manual.
For information on the system catalog tables associated with the SET
statement, see the sysobjstate and sysviolations tables in the Informix Guide
to SQL: Reference.
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Informix Guide to SQL: Syntax
SET CONNECTION
SET CONNECTION
The SET CONNECTION statement reestablishes a connection between an
application and a database environment and makes the connection current.
You can also use the SET CONNECTION statement with the DORMANT option
to put the current connection in a dormant state.
Syntax
ESQL
'connection name'
SET CONNECTION
E/C
+
+
conn_nm variable
+
Database
Environment
p. 1-94
DORMANT
DEFAULT
E/C
+
Element
connection
name
Purpose
Quoted string that identifies the
connection name that you
assigned to a specific
connection. It is the connection
name assigned by the CONNECT
statement when the initial
connection was made.
conn_nm
variable
Host variable that contains the
value of connection name
CURRENT
DORMANT
Restrictions
The database must already exist.
If you use the SET CONNECTION
statement with the DORMANT
option, connection name must
represent the current
connection. If you use the SET
CONNECTION statement
without the DORMANT option,
connection name must represent a
dormant connection.
Variable must be the character
data type.
Syntax
Quoted String,
p. 1-757
Variable name must
conform to
language-specific
rules for variable
names.
SQL Statements 1-527
SET CONNECTION
Usage
You can use the SET CONNECTION statement to change the state of a
connection in the following ways:
■
Make a dormant connection current
For information on using SET CONNECTION to make a dormant
connection current, see “Making a Dormant Connection the Current
Connection” below.
■
Make the current connection dormant
For information on using SET CONNECTION to make the current
connection dormant, see “Making a Current Connection Dormant”
on page 1-529.
Making a Dormant Connection the Current Connection
The SET CONNECTION statement, with no DORMANT option, makes the
specified dormant connection the current one. The connection that the application specifies must be dormant. The connection that is current when the
statement executes becomes dormant. A dormant connection is a connection
that has been established but is not current.
The SET CONNECTION statement in the following example makes connection
con1 the current connection and makes con2 a dormant connection:
CONNECT TO 'stores7' AS 'con1'
...
CONNECT TO 'demo7' AS 'con2'
...
SET CONNECTION 'con1'
A dormant connection has a connection context associated with it. When an
application makes a dormant connection current, it reestablishes that
connection to a database environment and restores its connection context.
(For more information on connection context, see page 1-91.) Reestablishing
a connection is comparable to establishing the initial connection, except that
it typically avoids authenticating the user’s permissions again, and it saves
reallocating resources associated with the initial connection. For example, the
application does not need to reprepare any statements that have previously
been prepared in the connection nor does it need to redeclare any cursors.
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Informix Guide to SQL: Syntax
SET CONNECTION
Making a Current Connection Dormant
The SET CONNECTION statement with the DORMANT option makes the
specified current connection a dormant connection. For example, the
following SET CONNECTION statement makes connection con1 dormant:
SET CONNECTION 'con1' DORMANT
The SET CONNECTION statement with the DORMANT option generates an
error if you specify a connection that is already dormant. For example, if
connection con1 is current and connection con2 is dormant, the following
SET CONNECTION statement returns an error message:
SET CONNECTION 'con2' DORMANT
However, the following SET CONNECTION statement executes successfully:
SET CONNECTION 'con1' DORMANT
Dormant Connections in a Single-Threaded Environment
In a single-threaded application (an ESQL/C application that does not use
threads or an ESQL/COBOL application), the DORMANT option makes the
current connection dormant. The availability of the DORMANT option in
single-threaded applications makes single-threaded ESQL/C applications
upwardly compatible with thread-safe ESQL/C applications.
Dormant Connections in a Thread-Safe ESQL/C Environment
E/C
As in a single-threaded application, a thread-safe ESQL/C application (an
ESQL/C application that uses threads) can establish many connections to one
or more databases. However, in the single-threaded environment, only one
connection can be active while the program executes. In the thread-safe
environment, there can be many threads (concurrent pieces of work
performing particular tasks) in one ESQL/C application, and each thread can
have one active connection.
SQL Statements 1-529
SET CONNECTION
An active connection is associated with a particular thread. Two threads
cannot share the same active connection. Once a thread makes an active
connection dormant, that connection is available to other threads. A dormant
connection is still established but is not currently associated with any thread.
For example, if the connection named con1 is active in the thread named
thread_1, the thread named thread_2 cannot make connection con1 its
active connection until thread_1 has made connection con1 dormant.
In a thread-safe ESQL/C application, the DORMANT option makes an active
connection dormant. Another thread can now use the connection by issuing
the SET CONNECTION statement without the DORMANT option.
The following code fragment from a thread-safe ESQL/C program shows
how a particular thread within a thread-safe application makes a connection
active, performs work on a table through this connection, and then makes the
connection dormant so that other threads can use the connection:
thread_2()
{
/* Make con2 an active connection */
EXEC SQL connect to 'db2' as 'con2';
/*Do insert on table t2 in db2*/
EXEC SQL insert into table t2 values(10);
/* make con2 available to other threads */
EXEC SQL set connection 'con2' dormant;
}
.
.
.
If a connection to a database environment is initiated with the WITH
CONCURRENT TRANSACTION clause of the CONNECT statement, an ongoing
transaction can used by any thread that subsequently connects to that
database environment. In addition, if an open cursor is associated with such
a connection, the cursor remains open when the connection is made dormant.
Threads within a thread-safe ESQL/C application can use the same cursor by
making the associated connection current even though only one thread can
use the connection at any given time.
For a detailed discussion of thread-safe ESQL/C applications and the use of
the SET CONNECTION statement in these applications, see Chapter 11 of the
INFORMIX-ESQL/C Programmer’s Manual. ♦
1-530
Informix Guide to SQL: Syntax
SET CONNECTION
Identifying the Connection
If the application did not use connection name in the initial CONNECT
statement, you must use a database environment (such as a database name
or a database pathname) as the connection name. For example, the following
SET CONNECTION statement uses a database environment for the connection
name because the CONNECT statement does not use connection name. For
information about quoted strings that contain a database environment , see
“Database Environment” on page 1-94.
CONNECT TO 'stores7'
...
CONNECT TO 'demo7'
...
SET CONNECTION 'stores7'
If a connection to a database server was assigned a connection name, however,
you must use the connection name to reconnect to the database server. An
error is returned if you use a database environment rather than the
connection name when a connection name exists.
The DEFAULT Option
Use the DEFAULT option to identify the default connection for a SET
CONNECTION statement. The default connection is one of the following
connections:
■
An explicit default connection (a connection established with the
CONNECT TO DEFAULT statement)
■
An implicit default connection (any connection made using the
DATABASE, CREATE DATABASE, or START DATABASE statements)
You can use SET CONNECTION without a DORMANT option to reestablish the
default connection or with the DORMANT option to make the default
connection dormant. See “The DEFAULT Option” on page 1-91 and “The
Implicit Connection with DATABASE Statements” on page 1-92 for more
information.
SQL Statements 1-531
SET CONNECTION
The CURRENT Keyword
Use the CURRENT keyword with the DORMANT option of the SET
CONNECTION statement as a shorthand form of identifying the current
connection. The CURRENT keyword replaces the current connection name. If
the current connection is con1, the following two statements are equivalent:
SET CONNECTION 'con1' DORMANT;
SET CONNECTION CURRENT DORMANT;
When a Transaction is Active
When you issue a SET CONNECTION statement without the DORMANT
option, the SET CONNECTION statement implicitly puts the current
connection in the dormant state. When you issue a SET CONNECTION
statement (with the DORMANT option), the SET CONNECTION statement
explicitly puts the current connection in the dormant state. In either case, the
statement can fail if a connection that becomes dormant has an uncommitted
transaction.
If the connection that becomes dormant has an uncommitted transaction, the
following conditions apply:
1-532
■
If the connection was established with the WITH CONCURRENT
TRANSACTION clause of the CONNECT statement, the SET
CONNECTION statement succeeds and puts the connection in a
dormant state.
■
If the connection was established without the WITH CONCURRENT
TRANSACTION clause of the CONNECT statement, the SET
CONNECTION statement fails and cannot set the connection to a
dormant state and the transaction in the current connection
continues to be active. The statement generates an error and the
application must decide whether to commit or roll back the active
transaction.
Informix Guide to SQL: Syntax
SET CONNECTION
When Current Connection Is to INFORMIX-OnLine Dynamic Server
Prior to Version 6.0
If the current connection is to a version of the OnLine database server prior
to 6.0, the following conditions apply when a SET CONNECTION statement
with or without the DORMANT option executes:
■
If the connection to be made dormant was established using the
WITH CONCURRENT TRANSACTION clause of the CONNECT
statement, the application can switch to a different connection.
■
If the connection to be made dormant was established without the
WITH CONCURRENT TRANSACTION clause of the CONNECT
statement, the application cannot switch to a different connection; the
SET CONNECTION statement returns an error. The application must
use the CLOSE DATABASE statement to close the database and drop
the connection.
References
See the CONNECT, DISCONNECT, and DATABASE statements in this manual.
In the INFORMIX-ESQL/C Programmer’s Manual, see the discussions of the
SET CONNECTION statement and thread-safe applications.
SQL Statements 1-533
SET DATASKIP
SET DATASKIP
The SET DATASKIP statement allows you to control whether OnLine skips a
dbspace that is unavailable (for example, due to a media failure) in the course
of processing a transaction.
Syntax
OL
+
SET DATASKIP
ON
,
dbspace
OFF
DEFAULT
Element
dbspace
Purpose
The name of the skipped
dbspace
Restrictions
The dbspace must exist at the
time the statement is executed.
Syntax
Identifier, p. 1-723
Usage
Use the SET DATASKIP statement to instruct the database server to skip a
dbspace that is unavailable during the course of processing a transaction.
ESQL
You receive a warning if a dbspace is skipped. The warning flag
sqlca.sqlwarn.sqlwarn6 is set to W if a dbspace is skipped. For more information about this topic, see the INFORMIX-ESQL/C Programmer’s Manual or
the INFORMIX-ESQL/COBOL Programmer’s Manual. ♦
When you SET DATASKIP ON without specifying a dbspace, you are telling
the database server to skip any dbspaces in the fragmentation list that are
unavailable. You can use the onstat -d or -D utility to determine if a dbspace
is down.
When you SET DATASKIP ON dbspace, you are telling the database server to
skip the specified dbspace if it is unavailable.
1-534
Informix Guide to SQL: Syntax
SET DATASKIP
Use the SET DATASKIP OFF statement to turn off the dataskip feature.
When the setting is DEFAULT, the database server uses the setting for the
dataskip feature from the ONCONFIG file. The OnLine administrator can
change the setting of the dataskip feature at runtime. See the
INFORMIX-OnLine Dynamic Server Administrator’s Guide for more
information.
Under What Circumstances Is a Dbspace Skipped?
The database server skips a dbspace when SET DATASKIP is set to ON and the
dbspace is unavailable.
The database server cannot skip a dbspace under certain conditions. The
following list outlines those conditions:
■
Referential constraint checking
When you want to delete a parent row, the child rows must also be
available for deletion. The child rows must exist in an available
fragment.
When you want to insert a new child table, the parent table must be
found in the available fragments.
■
Updates
When you perform an update that moves a record from one
fragment to another, both fragments must be available.
■
Inserts
When you try to insert records in a expression-based fragmentation
strategy and the dbspace is unavailable, an error is returned. When
you try to insert records in a round-robin fragment-based strategy,
and a dbspace is down, the database server inserts the rows into any
available dbspace. When no dbspace is available, an error is
returned.
SQL Statements 1-535
SET DATASKIP
■
Indexing
When you perform updates that affect the index, such as when you
insert or delete records, or when you update an indexed field, the
index must be available.
When you try to create an index, the dbspace you want to use must
be available.
■
Serial keys
The first fragment is used to store the current serial-key value internally. This is not visible to you except when the first fragment
becomes unavailable and a new serial key value is required, which
happens during insert statements.
References
For additional information about how to set the dataskip feature in the
ONCONFIG file and how to use the onspaces utility, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
1-536
Informix Guide to SQL: Syntax
SET DEBUG FILE TO
SET DEBUG FILE TO
Use the SET DEBUG FILE TO statement to name the file that is to hold the runtime trace output of a stored procedure.
Syntax
+
SET DEBUG FILE TO
'
filename
'
variable name
character
expression
Element
character
expression
filename
variable name
WITH APPEND
Purpose
Restrictions
An expression that evaluates to a The filename that is derived
filename
from the expression must be
usable. The same restrictions
apply to the derived filename as
to the filename parameter.
A quoted string that identifies
You can specify a new or existing
the pathname and filename of
file. If you specify an existing
the file that contains the output file, you must include the WITH
APPEND keywords if you want
of the TRACE statement. See
“Location of the Output File” on to preserve the current contents
page 1-539 for information on
of the file intact. See “Using the
the default actions that are taken WITH APPEND Option” on
if you omit the pathname.
page 1-538 for further
information.
A host variable that holds the
The host variable must be a
value of filename
character data type.
Syntax
Expression, p. 1-671
Quoted String,
p. 1-757. The
pathname and
filename must
conform to the
conventions of your
operating system.
The name of the host
variable must
conform to
language-specific
rules for variable
names.
SQL Statements 1-537
SET DEBUG FILE TO
Usage
This statement indicates that the output of the TRACE statement in the stored
procedure goes to the file that filename indicates. Each time the TRACE
statement is executed, the trace data is added to this output file.
Using the WITH APPEND Option
The output file that you specify in the SET DEBUG TO file statement can be a
new file or existing file.
If you specify an existing file, the current contents of the file are purged when
you issue the SET DEBUG TO FILE statement. The first execution of a TRACE
command sends trace output to the beginning of the file.
However, if you include the WITH APPEND option, the current contents of the
file are preserved when you issue the SET DEBUG TO FILE statement. The first
execution of a TRACE command adds trace output to the end of the file.
If you specify a new file in the SET DEBUG TO FILE statement, it makes no
difference whether you include the WITH APPEND option. The first execution
of a TRACE command sends trace output to the beginning of the new file
whether you include or omit the WITH APPEND option.
Closing the Output File
To close the file that the SET DEBUG FILE TO statement opened, issue another
SET DEBUG FILE TO statement with another filename. You can then edit the
contents of the first file.
Redirecting Trace Output
You can use the SET DEBUG FILE TO statement outside a procedure to direct
the trace output of the procedure to a file. You also can use this statement
inside a procedure to redirect its own output.
1-538
Informix Guide to SQL: Syntax
SET DEBUG FILE TO
Location of the Output File
If you invoke a SET DEBUG FILE TO statement with a simple filename on a
local database, the output file is located in your current directory. If your
current database is on a remote database server, the output file is located in
your home directory on the remote database server. If you provide a full
pathname for the debug file, the file is placed in the directory and file that you
specify on the remote database server. If you do not have write permissions
in the directory, you get an error.
Example of the SET DEBUG FILE TO Statement
The following example sends the output of the SET DEBUG FILE TO statement
to a file called debugging.out:
SET DEBUG FILE TO 'debugging' || '.out'
References
See the TRACE statement in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of stored procedures
in Chapter 12.
SQL Statements 1-539
SET DESCRIPTOR
SET DESCRIPTOR
Use the SET DESCRIPTOR statement to assign values to a system-descriptor
area.
Syntax
+
ESQL
'descriptor'
SET DESCRIPTOR
COUNT =
value
count
variable
descriptor
variable
VALUE
item
number
item
number
variable
Item
Descriptor
Information
TYPE
=
literal integer
integer-host
variable
LENGTH
PRECISION
SCALE
NULLABLE
INDICATOR
ITYPE
ILENGTH
DATA
IDATA
NAME
=
Literal Number
p. 1-752
Literal DATETIME
p. 1-746
Literal INTERVAL
p. 1-749
Quoted String
p. 1-757
data variable
1-540
Informix Guide to SQL: Syntax
,
Item
Descriptor
Information
SET DESCRIPTOR
Element
count variable
Purpose
Restrictions
A host variable that holds a
See restriction for value in this
literal integer. This integer
table.
specifies how many items are
actually described in the systemdescriptor area.
Syntax
The name of the host
variable must
conform to
language-specific
rules for variable
names.
The information that is
The name of the host
contained in data variable must be variable must
appropriate for the specified
conform to
field.
language-specific
rules for variable
names.
The system-descriptor area must Quoted String,
have been previously allocated p. 1-757
with the ALLOCATE
DESCRIPTOR statement.
The same restrictions apply to
The name of the host
descriptor variable as apply to
variable must
descriptor.
conform to
language-specific
rules for variable
names.
The same restrictions apply to
The name of the host
integer host variable as apply to
variable must
literal integer.
conform to
language-specific
rules for variable
names.
The value of item number must be Literal Number,
greater than 0 and less than (or p. 1-752
equal to) the number of occurrences that were specified when
the system-descriptor area was
allocated with the ALLOCATE
DESCRIPTOR statement.
data variable
A host variable that contains the
information for the specified
field (DATA, IDATA, or NAME) in
the specified item descriptor
descriptor
A string that identifies the
system-descriptor area to which
values will be assigned
descriptor
variable
A host variable that holds the
value of descriptor
integer host
variable
The name of a host variable that
contains the value of literal
integer
item number
An unsigned integer that
specifies one of the occurrences
(item descriptors) in the systemdescriptor area
(1 of 2)
SQL Statements 1-541
SET DESCRIPTOR
Element
item number
variable
Purpose
The name of an integer host
variable that holds the value of
item number
Restrictions
The same restrictions apply to
item number variable as apply to
item number.
Syntax
The name of the host
variable must
conform to
language-specific
rules for variable
names.
Literal Number,
p. 1-752
literal integer
A positive, nonzero integer that
assigns a value to the specified
field in the specified item
descriptor. The specified field
must be one of the following
keywords: TYPE, LENGTH,
PRECISION, SCALE, NULLABLE,
INDICATOR, ITYPE, or ILENGTH.
value
A literal integer that specifies
how many items are actually
described in the systemdescriptor area
The restrictions that apply to
literal integer vary with the field
type you specify in the VALUE
option (TYPE, LENGTH, and so
on). For information on the
codes that are allowed for the
TYPE field and their meaning,
see “Setting the TYPE Field” on
page 1-544. For the restrictions
that apply to other field types,
see the individual headings for
field types under “VALUE
Option” on page 1-543.
The integer that value specifies
Literal Number,
must be greater than 0 and less p. 1-752
than (or equal to) the number of
occurrences that were specified
when the system-descriptor area
was allocated with the
ALLOCATE DESCRIPTOR
statement.
(2 of 2)
Usage
Use the SET DESCRIPTOR statement to assign values to a system-descriptor
area in the following instances:
1-542
■
To set the COUNT field of a system-descriptor area to match the
number of items for which you are providing descriptions in the
system-descriptor area (typically the items are in a WHERE clause)
■
To set the item descriptor fields for each value for which you are
providing descriptions in the system-descriptor area (typically the
items are in a WHERE clause)
Informix Guide to SQL: Syntax
SET DESCRIPTOR
■
To modify the contents of an item-descriptor field after you use the
DESCRIBE statement to fill the fields for a SELECT or an INSERT
statement
If an error occurs during the assignment to any identified system-descriptor
fields, the contents of all identified fields are set to 0 or null, depending on
the variable type.
COUNT Option
Use the COUNT option to set the number of items that are to be used in the
system-descriptor area.
If you allocate a system-descriptor area with more items than you are using,
you need to set the COUNT field to the number of items that you are actually
using. The following example shows the sequence of statements in
INFORMIX-ESQL/C that can be used in a program:
EXEC SQL BEGIN DECLARE SECTION;
int count;
EXEC SQL END DECLARE SECTION;
EXEC SQL allocate descriptor 'desc_100'; /*allocates for 100 items*/
count = 2;
EXEC SQL set descriptor 'desc_100' count = :count;
VALUE Option
Use the VALUE option to assign values from host variables into fields for a
particular item in a system-descriptor area. You can assign values for items
for which you are providing a description (such as parameters in a WHERE
clause), or you can modify values for items that the database server described
during a DESCRIBE statement.
SQL Statements 1-543
SET DESCRIPTOR
Setting the TYPE Field
Use the following codes to set the value of TYPE for each item.
SQL Data Type
CHAR
SMALLINT
INTEGER
FLOAT
SMALLFLOAT
DECIMAL
SERIAL
DATE
MONEY
DATETIME
BYTE
TEXT
VARCHAR
INTERVAL
NCHAR
NVARCHAR
E/C
Integer Value
0
1
2
3
4
5
6
7
8
10
11
12
13
14
15
16
For code that is easier to maintain, use the predefined constants for these SQL
data types instead of their actual integer value. These constants are defined
in the sqltypes.h header file. ♦
The following example shows how you can set the TYPE field in ESQL/C:
main()
{
EXEC SQL BEGIN DECLARE SECTION;
int itemno, type;
EXEC SQL END DECLARE SECTION;
...
EXEC SQL allocate descriptor 'desc1' with max 5;
...
EXEC SQL set descriptor 'desc1' value 2 type = 5;
type = 2; itemno = 3;
EXEC SQL set descriptor 'desc1' value :itemno type = :type;
}
1-544
Informix Guide to SQL: Syntax
SET DESCRIPTOR
Compiling Without the -xopen Option
If you do not compile using the -xopen option, the regular Informix <vk>SQL
code is assigned for TYPE. You must be careful not to mix normal and X/Open
modes because errors can result. For example, if a particular type is not
defined under X/Open mode but is defined under normal mode, executing a
SET DESCRIPTOR statement can result in an error.
Setting the TYPE Field in X/Open Programs
X/O
In X/Open mode, you must use the X/Open set of integer codes for the data
type in the TYPE field. The following table shows the X/Open codes for data
types.
SQL Data Type
CHAR
SMALLINT
INTEGER
FLOAT
DECIMAL
Integer Value
1
4
5
6
3
If you use the ILENGTH, IDATA, or ITYPE fields in a SET DESCRIPTOR
statement, a warning message appears. The warning indicates that these
fields are not standard X/Open fields for a system-descriptor area. ♦
E/C
For code that is easier to maintain, use the predefined constants for these
X/Open SQL data types instead of their actual integer value. These constants
are defined in the sqlxtype.h header file. ♦
Setting the DATA Field
When you set the DATA field, you must provide the appropriate type of data
(character string for CHAR or VARCHAR, integer for INTEGER, and so on).
When any value other than DATA is set, the value of DATA is undefined. You
cannot set the DATA field for an item without setting TYPE for that item. If
you set the TYPE field for an item to a character type, you must also set the
LENGTH field. If you do not set the LENGTH field for a character item, you
receive an error.
SQL Statements 1-545
SET DESCRIPTOR
Using LENGTH or ILENGTH
If your DATA or IDATA field contains a character string, you must specify a
value for LENGTH. If you specify LENGTH=0, LENGTH sets automatically to
the maximum length of the string. The DATA or IDATA field can contain a
368-literal character string or a character string derived from a character
variable of CHAR or VARCHAR data type. This provides a method to
determine the length of a string in the DATA or IDATA field dynamically.
If a DESCRIBE statement precedes a SET DESCRIPTOR statement, LENGTH
automatically sets to the maximum length of the character field that is
specified in your table.
This information is identical for ILENGTH.
Using DECIMAL or MONEY Data Types
If you set the TYPE field for a DECIMAL or MONEY data type, and you want
to use a scale or precision other than the default values, set the SCALE and
PRECISION fields. You do not need to set the LENGTH field for a DECIMAL
or MONEY item; the LENGTH field is set accordingly from the SCALE and
PRECISION fields.
Using DATETIME or INTERVAL Data Types
If you set the TYPE field for a DATETIME or INTERVAL value, you can set the
DATA field as a literal DATETIME or INTERVAL or as a character string. If you
use a character string, you must set the LENGTH field to the encoded qualifier
value.
E/C
To determine the encoded qualifiers for a DATETIME or INTERVAL character
string, use the datetime and interval macros in the datetime.h header file.
If you set DATA to a host variable of DATETIME or INTERVAL, you do not need
to set LENGTH explicitly to the encoded qualifier integer. ♦
E/CO
1-546
To determine the encoded qualifiers for a DATETIME or INTERVAL character
string, use the ECO-IQU routine. ♦
Informix Guide to SQL: Syntax
SET DESCRIPTOR
Setting the INDICATOR Field
If you want to put a null value into the system-descriptor area, set the
INDICATOR field to -1, and do not set the DATA field.
If you set the INDICATOR field to 0 to indicate that the data is not null, you
must set the DATA field.
Setting the ITYPE Field
The ITYPE field expects an integer constant that indicates the data type of
your indicator variable. Use the same set of constants as for the TYPE field.
The constants are listed on page 1-544.
Modifying Values Set by the DESCRIBE Statement
You can use a DESCRIBE statement to modify the contents of a systemdescriptor area after it is set.
E/CO
To determine the encoded qualifiers for a DATETIME or INTERVAL character
string, use the ECO-IQU routine. See the INFORMIX-ESQL/COBOL
Programmer’s Manual for information on this routine.
After you use a DESCRIBE statement on SELECT or an INSERT statement, you
must check to determine whether the TYPE field is set to either 11 or 12 to
indicate a TEXT or BYTE data type. If TYPE contains an 11 or a 12, you must
use the SET DESCRIPTOR statement to reset TYPE to 116, which indicates FILE
type. ♦
References
See the ALLOCATE DESCRIPTOR, DEALLOCATE DESCRIPTOR, DECLARE,
DESCRIBE, EXECUTE, FETCH, GET DESCRIPTOR, OPEN, PREPARE, and PUT
statements in this manual for further information about using dynamic SQL
statements.
For further information about the system-descriptor area, see your SQL API
product manual.
SQL Statements 1-547
SET EXPLAIN
SET EXPLAIN
Use the SET EXPLAIN statement to obtain a measure of the work involved in
performing a query.
Syntax
+
SET EXPLAIN
ON
OFF
Usage
The SET EXPLAIN statement executes during the database server
optimization phase, which occurs when you initiate a query. For queries that
are associated with a cursor, if the query is prepared and does not have host
variables, optimization occurs when you prepare it; otherwise, it occurs
when you open the cursor.
When you issue a SET EXPLAIN ON statement, the path that the optimizer
chooses for each subsequent query is written to the sqexplain.out file. The
SET EXPLAIN ON statement remains in effect until you issue a SET EXPLAIN
OFF statement or until the program ends. The owner name (for example,
owner.customer) qualifies table names in the sqexplain.out file.
If the file already exists, subsequent output is appended to the file. If the
client application and the database server are on the same computer, the
sqexplain.out file is stored in your current directory.
When the current database is on another computer, the sqexplain.out file is
stored in your home directory on the remote host. If you do not have a home
directory on the remote host, the program stores sqexplain.out in the
directory from which the database server was started.
SE
1-548
If you do not have write privileges to a directory, INFORMIX-SE generates an
error. ♦
Informix Guide to SQL: Syntax
SET EXPLAIN
SET EXPLAIN Output
The SET EXPLAIN output file contains a copy of the query, a plan of execution
that the database-server optimizer selects, and an estimate of the amount of
work. The optimizer selects a plan to provide the most efficient way to
perform the query, based on such things as the presence and type of indexes
and the number of rows in each table.
The optimizer uses an estimate to compare the cost of one path with another.
The estimated cost does not translate directly into time. However, when data
distributions are used, a query with a higher estimate generally takes longer
to run than one with a smaller estimate.
The estimated cost of the query is included in the SET EXPLAIN output. In the
case of a query and a subquery, two estimated cost figures are returned; the
query figure also contains the subquery cost. The subquery cost is shown
only so you can see the cost that is associated with the subquery.
In addition to the estimated cost, the output file contains the following
information:
■
An estimate of the number of rows to be returned
■
The order in which tables are accessed during execution
■
The table column or columns that serve as a filter, if any, and whether
the filtering occurs through an index
■
The method (access path) by which the executor reads each table.
The following list shows the possible methods.
Method
Effect
SEQUENTIAL SCAN
Reads rows in sequence
INDEX PATH
Scans one or more indexes
AUTOINDEX PATH
Creates a temporary index
SORT SCAN
Sorts the result of the preceding join or table scan
MERGE JOIN
Uses a sort/merge join instead of nested-loop join
REMOTE PATH
Accesses another distributed database
HASH JOIN
Uses a hash join
SQL Statements 1-549
SET EXPLAIN
The optimizer chooses the best path of execution to produce the fastest
possible table join using a nested-loop join or sort-merge join wherever
appropriate.
The SORT SCAN section indicates that sorting the result of the preceding join
or table scan is necessary for a sort-merge join. It includes a list of the columns
that form the sort key. The order of the columns is the order of the sort. As
with indexes, the default order is ascending. Where possible, this ordering is
arranged to support any requested ORDER BY or GROUP BY clause. If the
ordering can be generated from a previous sort or an index lookup, the SORT
SCAN section does not appear.
The MERGE JOIN section indicates that a sort-merge join, instead of the
nested-loop join, is to be used on the preceding join/table pair. It includes a
list of the filters that control the sort-merge join and, where applicable, a list
of any other join filters. For example, a join of tables A and B with the filters
A.c1 = B.c1 and A.c2 < B.c2 lists the first join under “Merge Filters” and
the second join under “Other Join Filters.”
The DYNAMIC HASH JOIN section indicates that a hash join is to be used on
the preceding join/table pair. It includes a list of the filters used to join the
tables together.
A dynamic hash join uses one of the tables to construct a hash index and adds
the index for the other table into the hash index. This is referred to as the build
phase. If DYNAMIC HASH JOIN is followed by the (Build Outer) in the output,
then the build phase is occurring on the first table; otherwise it occurs on the
second table, preceding the DYNAMIC HASH JOIN. In the following example,
the build phase occurs on table username.a:
SELECT a.adatetime FROM manytypes a, alltypes b
WHERE a.adatetime = b.adate and a.along + 7 = b.along/3
Estimated Cost: 10
Estimated # of Rows Returned: 2
1) username.a: SEQUENTIAL SCAN
2) username.b: SEQUENTIAL SCAN
DYNAMIC HASH JOIN
Dynamic Hash Filters: username.a.adatetime =
username.b.adate and a.along + 7 = b.along/3
1-550
Informix Guide to SQL: Syntax
SET EXPLAIN
SE
When data distributions are not used, an INFORMIX-SE database server
generates fewer query-processing statistics than are available from an
OnLine database server. As a result, estimates for the cost and the number of
rows that are returned might be more precise if you use INFORMIX-OnLine
Dynamic Server than if you use INFORMIX-SE. Estimates returned for queries
that include joins tend to be highly inaccurate. ♦
The following output examples represent what you might see when a SET
EXPLAIN ON statement is issued using INFORMIX-OnLine Dynamic Server.
The first two examples contain two entries for a multiple-table query and
show the SORT SCAN and MERGE JOIN lines. Note that in both cases, if SORT
MERGE was not chosen, the second table would have been scanned using an
autoindex path. An autoindex path is an index constructed automatically at
execution time by the database server. It is removed when the query
completes.
QUERY:
----------select i.stock_num from items i, stock s, manufact m
where i.stock_num = s.stock_num
and i.manu_code = s.manu_code
and s.manu_code = m.manu_code
Estimated Cost: 52
Estimated # of Rows Returned: 130
1) rdtest.m: SEQUENTIAL SCAN
SORT SCAN: rdtest.m.manu_code
2) rdtest.s: SEQUENTIAL SCAN
SORT SCAN: rdtest.s.manu_code
MERGE JOIN:
Merge Filters: rdtest.m.manu_code = rdtest.s.manu_code
3) rdtest.i: INDEX PATH
(1) Index Keys: stock_num manu_code
Lower Index Filter: (rdtest.i.stock_num = rdtest.s.stock_num AND
rdtest.i.manu_code = rdtest.s.manu_code)
QUERY:
----------select stock.description from stock, stock2
where stock.description = stock2.description
and stock.unit_price < stock2.unit_price
Estimated Cost: 15
Estimated # of Rows Returned: 370
1) rdtest.stock: SEQUENTIAL SCAN
SQL Statements 1-551
SET EXPLAIN
Lower Index Filter: joe.customer.customer_num = joe.orders.customer_num
3) joe.items: INDEX PATH
(1) Index Keys: order_num
Lower Index Filter: joe.items.order_num
= joe.orders.order_num
SET EXPLAIN Output with Fragmentation and PDQ
When the table is fragmented, the output shows which table or index is
scanned. Fragments are identified with a fragment number. The fragment
numbers are the same as those contained in the dbspace column in the
sysfragments system catalog table. If the optimizer must scan all fragments
(that is, if it is unable to eliminate any fragment from consideration), the
optimizer indicates this with ALL. In addition, if the optimizer eliminates all
the fragments from consideration, that is, none of the fragments contain the
queried information, the optimizer indicates this with NONE. For information on how OnLine eliminates a fragment from consideration, see the
INFORMIX-OnLine Dynamic Server Administrator’s Guide.
When PDQ is turned on, the output shows whether the optimizer used
parallel scans. If the optimizer used parallel scans, the output shows
PARALLEL; if PDQ is turned off, the output shows SERIAL. If PDQ is turned
on, the optimizer indicates the maximum number of threads that are required
to answer the query. The output shows # of Secondary Threads. This field
indicates the number of threads that are required in addition to your user
session thread. The total number of threads necessary is the number of
secondary threads plus 1.
The output indicates when a hash join is used. The query is marked with
DYNAMIC HASH JOIN, and the table on which the hash is built is marked with
Build Outer.
The following example shows the SET EXPLAIN output for a table with
fragmentation and PDQ priority set to low:
select * from t1 where c1 > 20
Estimated Cost: 2
Estimated # of Rows Returned: 2
1) informix.t1: SEQUENTIAL SCAN (Parallel, fragments: 2)
Filters: informix.t1.c1 > 20
# of Secondary Threads = 1
SQL Statements 1-553
SET EXPLAIN
The following example of SET EXPLAIN output shows a table with
fragmentation but without PDQ:
select * from t1 where c1 > 12
Estimated Cost: 3
Estimated # of Rows Returned: 2
1) informix.t1: SEQUENTIAL SCAN (Serial, fragments: 1, 2)
Filters: informix.t1.c1 > 12
The following example of SET EXPLAIN output shows a table with hash join
(fragmentation, and PDQ priority set to ON). The hash join is created when
you create an equality join between two tables that are not indexed.
QUERY:
-----select h1.c1, h2.c1 from h1, h2 where h1.c1=h2.c1
Estimated Cost: 2
Estimated # of Rows Returned: 5
1) informix.h1: SEQUENTIAL SCAN (Parallel, fragments: ALL)
2) informix.h2: SEQUENTIAL SCAN (Parallel, fragments: ALL)
DYNAMIC HASH JOIN (Build Outer)
Dynamic Hash Filters: informix.h1.c1 = informix.h2.c1
# of Secondary Threads = 6
The following example of SET EXPLAIN output shows a table with
fragmentation, with PDQ priority set to LOW, and an index that was selected
as the search method:
QUERY:
-----select * from t1 where c1 < 13
Estimated Cost: 2
Estimated # of Rows Returned: 1
1) informix.t1: INDEX PATH
(1) Index Keys: c1 (Parallel, fragments: ALL)
Upper Index Filter: informix.t1.c1 < 13
# of Secondary Threads = 3
1-554
Informix Guide to SQL: Syntax
SET EXPLAIN
Using SET EXPLAIN With SET OPTIMIZATION
If you SET OPTIMIZATION to low, the output of SET EXPLAIN displays the
following uppercase string:
QUERY:{LOW}
If you SET OPTIMIZATION to high, the output of SET EXPLAIN displays the
following uppercase string:
QUERY:
Reference
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of SET EXPLAIN and the optimizer discussion.
SQL Statements 1-555
SET ISOLATION
SET ISOLATION
Use the SET ISOLATION statement with the INFORMIX-OnLine Dynamic
Server database server to define the degree of concurrency among processes
that attempt to access the same rows simultaneously.
The SET ISOLATION statement is an Informix extension to the ANSI SQL-92
standard. If you want to set isolation levels through an ANSI-compliant
statement, use the SET TRANSACTION statement instead. See the SET
TRANSACTION statement on page 1-575 for a comparison of these two
statements.
Syntax
OL
+
SET ISOLATION TO
DIRTY READ
COMMITTED READ
CURSOR STABILITY
REPEATABLE READ
Usage
The database isolation level affects read concurrency when rows are retrieved
from the database. INFORMIX-OnLine Dynamic Server uses shared locks to
support four levels of isolation among processes attempting to access data.
The update or delete process always acquires an exclusive lock on the row
that is being modified. The level of isolation does not interfere with rows that
you are updating or deleting. If another process attempts to update or delete
rows that you are reading with an isolation level of Repeatable Read, that
process will be denied access to those rows.
1-556
Informix Guide to SQL: Syntax
SET ISOLATION
ESQL
Cursors that are currently open when you execute the SET ISOLATION
statement might or might not use the new isolation level when rows are later
retrieved. The isolation level in effect could be any level that was set from the
time the cursor was opened until the time the application actually fetches a
row. The database server might have read rows into internal buffers and
internal temporary tables using the isolation level that was in effect at that
time. To ensure consistency and reproducible results, close open cursors
before you execute the SET ISOLATION statement. ♦
Informix Isolation Levels
The following definitions explain the critical characteristics of each isolation
level, from the lowest level of isolation to the highest.
Isolation Level
Characteristics
Dirty Read
Provides zero isolation. Dirty Read is appropriate for static
tables that are used for queries. With a Dirty Read isolation
level, a query might return a phantom row, which is an uncommitted row that was inserted or modified within a transaction
that has subsequently rolled back. No other isolation level
allows access to a phantom row. Dirty Read is the only
isolation level available to databases that do not have
transactions.
Committed Read
Guarantees that every retrieved row is committed in the table
at the time that the row is retrieved. Even so, no locks are
acquired. After one process retrieves a row because no lock is
held on the row, another process can acquire an exclusive lock
on the same row and modify or delete data in the row.
Committed Read is the default level of isolation in a database
with logging that is not ANSI compliant.
(1 of 2)
SQL Statements 1-557
SET ISOLATION
Isolation Level
Characteristics
Cursor Stability
Acquires a shared lock on the selected row. Another process
can also acquire a shared lock on the same row, but no process
can acquire an exclusive lock to modify data in the row. When
you fetch another row or close the cursor, INFORMIX-OnLine
Dynamic Server releases the shared lock.
If you set the isolation level to Cursor Stability, but you are not
using a transaction, the Cursor Stability isolation level acts
like the Committed Read isolation level. Locks are acquired
when the isolation level is set to Cursor Stability outside a
transaction, but they are released immediately at the end of
the statement that reads the row.
Repeatable Read
Acquires a shared lock on every row that is selected during the
transaction. Another process can also acquire a shared lock on
a selected row, but no other process can modify any selected
row during your transaction. If you repeat the query during
the transaction, you reread the same information. The shared
locks are released only when the transaction commits or rolls
back. Repeatable Read is the default isolation level in an ANSIcompliant database.
(2 of 2)
Default Isolation Levels
The default isolation level for a particular database is established when you
create the database according to database type. The following list describes
the default isolation level for each database type.
1-558
Isolation Level
Database Type
Dirty Read
Default level of isolation in a database without logging
Committed Read
Default level of isolation in a database with logging that is not
ANSI compliant
Repeatable Read
Default level of isolation in an ANSI-compliant database
Informix Guide to SQL: Syntax
SET ISOLATION
The default level remains in effect until you issue a SET ISOLATION statement.
After a SET ISOLATION statement executes, the new isolation level remains in
effect until one of the following events occurs:
■
You enter another SET ISOLATION statement.
■
You open another database that has a default isolation level different
from the isolation level that your last SET ISOLATION statement
specified.
■
The program ends.
Effects of Isolation Levels
You cannot set the database isolation level in a database that does not have
logging. Every retrieval in such a database occurs as a Dirty Read.
You can issue a SET ISOLATION statement from a client computer only after a
database has been opened.
The data obtained during blob retrieval can vary, depending on the database
isolation level. Under Dirty Read or Committed Read levels of isolation, a
process is permitted to read a blob that is either deleted (if the delete is not
yet committed) or in the process of being deleted. Under these isolation
levels, an application can read a deleted blob when certain conditions exist.
See the INFORMIX-OnLine Dynamic Server Administrator’s Guide for information about these conditions.
DB
ESQL
When you use DB-Access, you see more lock conflicts with higher levels of
isolation. For example, if you use Cursor Stability, you see more lock conflicts
than if you use Committed Read. ♦
If you use a scroll cursor in a transaction, you can force consistency between
your temporary table and the database table either by setting the isolation
level to Repeatable Read or by locking the entire table during the transaction.
If you use a scroll cursor with hold in a transaction, you cannot force consistency between your temporary table and the database table. A table-level
lock or locks that are set by Repeatable Read are released when the
transaction is completed, but the scroll cursor with hold remains open
beyond the end of the transaction. You can modify released rows as soon as
the transaction ends, but the retrieved data in the temporary table might be
inconsistent with the actual data. ♦
SQL Statements 1-559
SET ISOLATION
References
See the CREATE DATABASE, SET LOCK MODE, and SET TRANSACTION
statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of isolation levels in
Chapter 7.
1-560
Informix Guide to SQL: Syntax
SET LOCK MODE
SET LOCK MODE
Use the SET LOCK MODE statement to define how the database server
handles a process that tries to access a locked row or table.
Syntax
+
SET LOCK MODE TO
WAIT
OL
seconds
NOT WAIT
Element
seconds
Purpose
The maximum number of
seconds that a process waits for a
lock to be released. If the lock is
still held at the end of the
waiting period, the database
server ends the operation and
returns an error code to the
process.
Restrictions
Syntax
In a networked environment, the Literal Number,
DBA establishes a default value p. 1-752
for the waiting period by using
the ONCONFIG parameter
DEADLOCK_TIMEOUT. See
“WAIT Keyword” on page 1-562
for an explanation of when the
seconds parameter overrides the
DEADLOCK_TIMEOUT
parameter.
SQL Statements 1-561
SET LOCK MODE
Usage
You can direct the response of the database server in the following ways
when a process tries to access a locked row or table.
SE
Lock Mode
Effect
NOT WAIT
Ends the operation immediately and returns an error code.
This condition is the default.
WAIT
Suspends the process until the lock releases
WAIT seconds
Suspends the process until the lock releases or until the end of
a waiting period, which is specified in seconds. If the lock
remains after the waiting period, it ends the operation and
returns an error code.
INFORMIX-SE does not support the seconds parameter. If you decide that a
process should wait for a lock to release, you cannot limit the waiting period.
The SET LOCK MODE statement is available on computers that use kernel
locking. To determine whether your computer uses kernel locking, check the
directory that holds the database files. If the directory contains files with the
extension .lok, your system does not use kernel locking, and the SET LOCK
MODE statement is unavailable. ♦
WAIT Keyword
The database server protects against the possibility of a deadlock when you
request the WAIT option. Before the database server suspends a process, it
checks whether suspending the process could create a deadlock. If the
database server discovers that a deadlock could occur, it ends the operation
(overruling your instruction to wait) and returns an error code. In the case of
either a suspected or actual deadlock, the database server returns an error.
Cautiously use the unlimited waiting period that was created when you
specify the WAIT option without seconds. If you do not specify an upper limit,
and the process that placed the lock somehow fails to release it, suspended
processes could wait indefinitely. Because a true deadlock situation does not
exist, the database server does not take corrective action.
1-562
Informix Guide to SQL: Syntax
SET LOCK MODE
In a networked environment, the DBA uses the ONCONFIG parameter
DEADLOCK_TIMEOUT to establish a default value for seconds. If you use a SET
LOCK MODE statement to set an upper limit, your value applies only when
your waiting period is shorter than the system default. The number of
seconds that the process waits applies only if you acquire locks within the
current database server and a remote database server within the same
transaction.
References
See the LOCK TABLE, UNLOCK TABLE, SET ISOLATION, and SET
TRANSACTION statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of SET LOCK MODE
in Chapter 7.
SQL Statements 1-563
SET LOG
SET LOG
Use the SET LOG statement to change your INFORMIX-OnLine Dynamic
Server database logging mode from buffered transaction logging to
unbuffered transaction logging or vice versa.
Syntax
OL
+
SET
LOG
BUFFERED
Usage
You activate transaction logging when you create a database or add logging
to an existing database. These transaction logs can be buffered or unbuffered.
The default condition for transaction logs is unbuffered logging. As soon as
a transaction ends, the OnLine database server writes the transaction to the
disk. If a system failure occurs when you are using unbuffered logging, you
recover all completed transactions.
You gain a marginal increase in efficiency with buffered logging, but you
incur some risk. In the event of a system failure, the OnLine database server
cannot recover the completed transactions that were buffered in memory.
The SET LOG statement changes the transaction-logging mode to unbuffered
logging; the SET BUFFERED LOG statement changes the mode to buffered
logging.
The SET LOG statement redefines the mode for the current session only. The
default mode, which the OnLine administrator sets using ON-Monitor,
remains unchanged.
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Informix Guide to SQL: Syntax
SET LOG
The buffering option does not affect retrievals from external tables. For
distributed queries, a database with logging can retrieve only from databases
with logging, but it makes no difference whether the databases use buffered
or unbuffered logging.
ANSI
An ANSI-compliant database cannot use buffered logs. ♦
References
See the CREATE DATABASE and START DATABASE statements in this manual.
SQL Statements 1-565
SET OPTIMIZATION
SET OPTIMIZATION
Use the SET OPTIMIZATION statement to specify a high or low level of
database-server optimization.
Syntax
+
SET OPTIMIZATION
HIGH
LOW
Usage
You can execute a SET OPTIMIZATION statement at any time. The
optimization level carries across databases but applies only within the
current database server.
After a SET OPTIMIZATION statement executes, the new optimization level
remains in effect until you enter another SET OPTIMIZATION statement or
until the program ends.
The default database server optimization level, HIGH, remains in effect until
you issue another SET OPTIMIZATION statement. The LOW option invokes a
less sophisticated, but faster, optimization algorithm.
The algorithm that a SET OPTIMIZATION HIGH statement invokes is a
sophisticated, cost-based strategy that examines all reasonable choices and
selects the best overall alternative. For large joins, this algorithm can incur
more overhead than desired. In extreme cases, you can run out of memory.
The alternative algorithm that a SET OPTIMIZATION LOW statement invokes
eliminates unlikely join strategies during the early stages, which reduces the
time and resources spent during optimization. However, when you specify a
low level of optimization, the optimal strategy might not be selected because
it was eliminated from consideration during early stages of the algorithm.
1-566
Informix Guide to SQL: Syntax
SET OPTIMIZATION
The following example shows optimization across a network. The central
database (on computer 1) is to have LOW optimization; the western database
(on computer 2) is to have HIGH optimization. If the western database were
on the same computer as central, it would have LOW optimization.
CONNECT TO 'central';
SET OPTIMIZATION low;
SELECT catalog.*, description, unit_price, unit,
unit_descr, manu_name, lead_time
FROM catalog, stock, manufact
WHERE catalog.stock_num = stock.stock_num
AND stock.manu_code = manufact.manu_code
AND catalog_num = 10025
CLOSE DATABASE;
CONNECT TO 'western@rockie';
SET OPTIMIZATION low;
SELECT catalog.*, description, unit_price, unit,
unit_descr, manu_name, lead_time
FROM catalog, stock, manufact
WHERE catalog.stock_num = stock.stock_num
AND stock.manu_code = manufact.manu_code
AND catalog_num = 10025
Optimizing Stored Procedures
For stored procedures that remain unchanged or change only slightly, you
might want to set the SET OPTIMIZATION statement to HIGH when you create
the procedure. This stores the best query plans for the procedure. Then SET
OPTIMIZATION to LOW before you execute the procedure. The procedure
then uses the optimal query plans and runs at the more cost-effective rate.
References
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of optimizing queries.
SQL Statements 1-567
SET PDQPRIORITY
SET PDQPRIORITY
The SET PDQPRIORITY statement allows an application to set the query
priority level dynamically within an application.
Syntax
OL
+
SET PDQPRIORITY
DEFAULT
LOW
OFF
HIGH
percent-of-resources
Element
percent-ofresources
Purpose
An integer value that specifies
the query priority level and the
amount of resources the
database server uses in order to
process the query
Restrictions
Syntax
You must specify a value in the Literal Number,
following range: -1, 0, 1 to 100. p. 1-752
The values -1, 0, and 1 have
special meanings. See “Meaning
of SET PDQPRIORITY Parameters” on page 1-569 for an
explanation of these values.
Usage
Priority set with the SET PDQPRIORITY statement overrides the environment
variable PDQPRIORITY. However, no matter what priority value you set with
the SET PDQPRIORITY statement, the ONCONFIG configuration parameter
MAX_PDQPRIORITY determines the actual priority value that the
INFORMIX-OnLine Dynamic Server uses for your queries.
For example, assume that the DBA has set the MAX_PDQPRIORITY parameter
to 50. A user enters the following SET PDQPRIORITY statement to set the
query priority level to 80.
SET PDQPRIORITY 80
1-568
Informix Guide to SQL: Syntax
SET PDQPRIORITY
When it processes the user’s query, OnLine uses the value of the
MAX_PDQPRIORITY parameter to factor the query priority level set by the
user. OnLine silently processes the query with a priority level of 40. This
priority level represents 50 percent of the 80 percent of resources specified by
the user.
Meaning of SET PDQPRIORITY Parameters
The parameters that the SET PDQPRIORITY statement can use are shown in
the following table.
Parameter
Meaning
DEFAULT
Uses the value that is specified in the PDQPRIORITY environment
variable, if any. DEFAULT is the symbolic equivalent of -1.
LOW
Signifies that data is fetched from fragmented tables in parallel.
OnLine uses no other forms of parallelism. LOW is the symbolic
equivalent of 1.
OFF
Indicates that PDQ is turned off. OnLine uses no parallelism. OFF is
the symbolic equivalent of 0. OFF is the default setting if you do not
specify the PDQPRIORITY environment variable or the SET
PDQPRIORITY statement.
HIGH
Signifies that the database server determines an appropriate value
to use for PDQPRIORITY. This decision is based on several things,
including the number of available processors, the fragmentation of
the tables being queried, the complexity of the query, and so on.
Informix reserves the right to change the performance behavior of
queries when HIGH is specified in future releases.
percent-ofresources
Indicates a query priority level and indicates the percent of
resources a database server uses in order to answer the query.
Resources include the amount of memory and the number of
processors. The higher the number, the more resources the
database server uses. Although usually the more resources a
database server uses indicates better performance for a given
query, using too many resources can cause contention among the
resources and remove resources from other queries, which results
in degraded performance. Range = -1, 0, 1 to 100.
SQL Statements 1-569
SET PDQPRIORITY
References
For information about the PDQPRIORITY environment variable, see the
Informix Guide to SQL: Reference. See the INFORMIX-OnLine Dynamic Server
Administrator’s Guide for information about the ONCONFIG parameter
MAX_PDQPRIORITY.
1-570
Informix Guide to SQL: Syntax
SET ROLE
SET ROLE
Use the SET ROLE statement to enable the privileges of a role.
Syntax
+
SET ROLE
role name
OL
NULL
NONE
Element
Purpose
Restrictions
Syntax
role name
Name of the role that you want
to enable
The role must have been created Identifier, p. 1-723
with the CREATE ROLE
statement.
Usage
Any user who is granted a role can enable the role using the SET ROLE
statement. A user can only enable one role at a time. If a user executes the SET
ROLE statement after a role is already set, the new role replaces the old role.
All users are, by default, assigned the role NULL or NONE (NULL and NONE
are synonymous). The roles NULL and NONE have no privileges. When you
set the role to NULL or NONE, you disable the current role.
When a user sets a role, the user gains the privileges of the role, in addition
to the privileges of PUBLIC and the user’s own privileges. If a role is granted
to another role, the user gains the privileges of both roles, in addition to those
of PUBLIC and the user’s own privileges. After a SET ROLE statement executes
successfully, the role remains effective until the current database is closed or
the user executes another SET ROLE statement. Additionally, the user, not the
role, retains ownership of all the objects, such as tables, that were created
during a session.
A user cannot execute the SET ROLE statement while in a transaction. If the
SET ROLE statement is executed while a transaction is active, an error occurs.
SQL Statements 1-571
SET ROLE
If the SET ROLE statement is executed as a part of a trigger or stored
procedure, and the owner of the trigger or stored procedure was granted the
role with the WITH GRANT OPTION, the role is enabled even if the user is not
granted the role.
The following example sets the role engineer:
SET ROLE engineer
The following example sets a role and then relinquishes the role after it
performs a SELECT operation:
EXEC SQL set role engineer;
EXEC SQL select fname, lname, project
into :efname, :elname, :eproject
where project_num > 100 and lname = 'Larkin';
printf ("%s is working on %s\n", efname, eproject);
EXEC SQL set role null;
References
See the CREATE ROLE, DROP ROLE, GRANT, and REVOKE statements in this
manual.
1-572
Informix Guide to SQL: Syntax
SET SESSION AUTHORIZATION
SET SESSION AUTHORIZATION
The SET SESSION AUTHORIZATION statement lets you change the user name
under which database operations are performed in the current OnLine
session. This statement is enabled by the DBA privilege, which you must
obtain from the DBA before the start of your current session. The new identity
remains in effect in the current database until you execute another SET
SESSION AUTHORIZATION statement or until you close the current database.
Syntax
ESQL
SET SESSION AUTHORIZATION TO
OL
Element
Purpose
Restrictions
' user '
The user name under which
You must specify a valid user
database operations are to be
name. You must put quotation
performed in the current session marks around the user name.
' user'
Syntax
Identifier, p. 1-723
Usage
The SET SESSION AUTHORIZATION statement allows a user with the DBA
privilege to bypass the privileges that protect database objects. You can use
this statement to gain access to a table and adopt the identity of a table owner
to grant access privileges. You must obtain the DBA privilege before you start
a session in which you use this statement. Otherwise, this statement returns
an error.
When you use this statement, the user name to which the authorization is set
must have the Connect privilege on the current database. Additionally, the
DBA cannot set the authorization to PUBLIC or to any defined role in the
current database.
SQL Statements 1-573
SET SESSION AUTHORIZATION
Setting a session to another user causes a change in a user name in the current
active database server. In other words, these users are, as far as this database
server process is concerned, completely dispossessed of any privileges that
they might have while accessing the database server through some administrative utility. Additionally, the new session user is not able to initiate an
administrative operation (execute a utility, for example) by virtue of the
acquired identity.
After the SET SESSION AUTHORIZATION statement successfully executes, the
user must use the SET ROLE statement to assume a role granted to the current
user. Any role enabled by a previous user is relinquished.
Using SET SESSION AUTHORIZATION to Obtain Privileges
You can use the SET SESSION AUTHORIZATION statement either to obtain
access to the data directly or to grant the database-level or table-level
privileges needed for the database operation to proceed. The following
example shows how to use the SET SESSION AUTHORIZATION statement to
obtain table-level privileges:
SET SESSION AUTHORIZATION TO 'cathl';
GRANT ALL ON spec TO mary;
SET SESSION AUTHORIZATION TO 'mary';
UPDATE case
SET col1 = SELECT state FROM zip
WHERE zip_code = 94433;
References
See the CONNECT, DATABASE, GRANT, and SET ROLE statements in this
manual.
1-574
Informix Guide to SQL: Syntax
SET TRANSACTION
SET TRANSACTION
Use the SET TRANSACTION statement to define isolation levels and to define
the access mode of a transaction (read-only or read-write).
Syntax
,
SET TRANSACTION
1
READ WRITE
READ ONLY
OL
1
ISOLATION LEVEL
READ COMMITTED
REPEATABLE READ
SERIALIZABLE
,
1
READ ONLY
OL
1
ISOLATION LEVEL
READ UNCOMMITTED
Usage
You can use SET TRANSACTION only in databases with logging.
You can issue a SET TRANSACTION statement from a client computer only
after a database has been opened.
SQL Statements 1-575
SET TRANSACTION
The database isolation level affects concurrency among processes that
attempt to access the same rows simultaneously from the database.
INFORMIX-OnLine Dynamic Server uses shared locks to support four levels
of isolation among processes that are attempting to read data as the following
list shows:
■
Read Uncommitted
■
Read Committed
■
(ANSI) Repeatable Read
■
Serializable
The update or delete process always acquires an exclusive lock on the row
that is being modified. The level of isolation does not interfere with rows that
you are updating or deleting; however, the access mode does affect whether
you can update or delete rows. If another process attempts to update or
delete rows that you are reading with an isolation level of Serializable or
(ANSI) Repeatable Read, that process will be denied access to those rows.
Comparing SET TRANSACTION with SET ISOLATION
The SET TRANSACTION statement complies with ANSI SQL-92. This statement
is similar to the Informix SET ISOLATION statement; however, the SET
ISOLATION statement is not ANSI compliant and does not provide access
modes. In fact, the isolation levels that you can set with the SET
TRANSACTION statement are almost parallel to the isolation levels that you
can set with the SET ISOLATION statement, as the following table shows.
SET TRANSACTION
1-576
Correlates to
SET ISOLATION
Read Uncommitted
Dirty Read
Read Committed
Committed Read
Not supported
Cursor Stability
(ANSI) Repeatable Read
(Informix) Repeatable Read
Serializable
(Informix) Repeatable Read
Informix Guide to SQL: Syntax
SET TRANSACTION
Another difference between the SET TRANSACTION and SET ISOLATION
statements is the behavior of the isolation levels within transactions. The SET
TRANSACTION statement can be issued only once for a transaction. Any
cursors that are opened during that transaction are guaranteed to get that
isolation level (or access mode if you are defining an access mode). With the
SET ISOLATION statement, after a transaction is started, you can change the
isolation level more than once within the transaction. The following
examples show the SET ISOLATION and SET TRANSACTION statements,
respectively:
SET ISOLATION
EXEC
EXEC
EXEC
EXEC
EXEC
EXEC
SQL BEGIN WORK;
SQL SET ISOLATION TO DIRTY READ;
SQL SELECT ... ;
SQL SET ISOLATION TO REPEATABLE READ;
SQL INSERT ... ;
SQL COMMIT WORK;
-- Executes without error
SET TRANSACTION
EXEC SQL BEGIN WORK;
EXEC SQL SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
EXEC SQL SELECT ... ;
EXEC SQL SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
Error 876: Cannot issue SET TRANSACTION in an active
transaction.
SQL Statements 1-577
SET TRANSACTION
Isolation Levels
The following definitions explain the critical characteristics of each isolation
level, from the lowest level of isolation to the highest.
1-578
Isolation Level
Characteristics
Read Uncommitted
Provides zero isolation. Read Uncommitted is appropriate
for static tables that are used for queries. With a Read
Uncommitted isolation level, a query might return a
phantom row, which is an uncommitted row that was
inserted or modified within a transaction that has subsequently rolled back. Read Uncommitted is the only
isolation level that is available to databases that do not
have transactions.
Read Committed
Guarantees that every retrieved row is committed in the
table at the time that the row is retrieved. Even so, no locks
are acquired. After one process retrieves a row because no
lock is held on the row, another process can acquire an
exclusive lock on the same row and modify or delete data
in the row. Read Committed is the default isolation level in
a database with logging that is not ANSI compliant.
(ANSI) Repeatable
Read
The Informix implementation of ANSI Repeatable Read.
Informix uses the same approach to implement Repeatable
Read that it uses for Serializable. Thus Repeatable Read
meets the SQL-92 requirements.
Serializable
Acquires a shared lock on every row that is selected during
the transaction. Another process can also acquire a shared
lock on a selected row, but no other process can modify any
selected row during your transaction. If you repeat the
query during the transaction, you reread the same information. The shared locks are released only when the
transaction commits or rolls back. Serializable is the
default isolation level in an ANSI-compliant database.
Informix Guide to SQL: Syntax
SET TRANSACTION
Default Isolation Levels
The default isolation level for a particular database is established according
to database type when you create the database. The default isolation level for
each database type is described in the following table.
Informix
ANSI
Description
Dirty Read
Read Uncommitted
Default level of isolation in a
database without logging
Committed Read
Read Committed
Default level of isolation in a
database with logging that is not
ANSI compliant
Repeatable Read
Serializable
Default level of isolation in an ANSIcompliant database
The default isolation level remains in effect until you issue a SET
TRANSACTION statement within a transaction. After a COMMIT WORK
statement completes the transaction or a ROLLBACK WORK statement cancels
the transaction, the isolation level is reset to the default.
Access Modes
Both INFORMIX-OnLine Dynamic Server and INFORMIX-SE support access
modes. Access modes affect read and write concurrency for rows within
transactions. Use access modes to control data modification.
You can specify that a transaction is read-only or read-write through the SET
TRANSACTION statement. By default, transactions are read-write. When you
specify that a transaction is read-only, certain limitations apply. Read-only
transactions cannot perform the following actions:
■
Insert, delete, or update table rows
■
Create, alter, or drop any database object such as schemas, tables,
temporary tables, indexes, or stored procedures
■
Grant or revoke privileges
■
Update statistics
■
Rename columns or tables
SQL Statements 1-579
SET TRANSACTION
You can execute stored procedures in a read-only transaction as long as the
procedure does not try to perform any restricted statement.
Effects of Isolation Levels
You cannot set the database isolation level in a database that does not have
logging. Every retrieval in such a database occurs as a Read Uncommitted.
The data that is obtained during blob retrieval can vary, depending on the
database isolation levels. Under Read Uncommitted or Read Committed
isolation levels, a process is permitted to read a blob that is either deleted (if
the delete is not yet committed) or in the process of being deleted. Under
these isolation levels, an application can read a deleted blob when certain
conditions exist. See the INFORMIX-OnLine Dynamic Server Administrator’s
Guide for information about these conditions.
ESQL
If you use a scroll cursor in a transaction, you can force consistency between
your temporary table and the database table either by setting the isolation
level to Serializable or by locking the entire table during the transaction.
If you use a scroll cursor with hold in a transaction, you cannot force
consistency between your temporary table and the database table. A tablelevel lock or locks set by Serializable are released when the transaction is
completed, but the scroll cursor with hold remains open beyond the end of
the transaction. You can modify released rows as soon as the transaction
ends, so the retrieved data in the temporary table might be inconsistent with
the actual data. ♦
References
See the CREATE DATABASE, SET ISOLATION, and SET LOCK MODE statements
in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of isolation levels and
concurrency issues in Chapter 7.
1-580
Informix Guide to SQL: Syntax
START DATABASE
START DATABASE
Use the START DATABASE statement with an INFORMIX-SE database server to
start recording transactions, to make a database ANSI compliant, to change
the name of an existing transaction-log file, or to remove logging on a
database.
Syntax
SE
+
START DATABASE
Database
Name
p. 1-660
WITH LOG IN
'pathname'
MODE ANSI
WITH NO LOG
Element
pathname
Purpose
The pathname and filename of
the transaction log file. The
default directory is the current
directory.
Restrictions
You cannot specify an existing
file in pathname. You must
specify an existing directory in
pathname. For maximum
protection, you should specify a
location for the transaction-log
file that is not on the same
storage device as the database.
Syntax
The pathname and
filename must
conform to the
conventions of your
operating system.
Usage
To use the START DATABASE statement, all the following conditions must be
true:
■
You have the DBA privilege.
■
No current database exists.
■
The directory that is specified in pathname exists.
SQL Statements 1-581
START DATABASE
Issue a CLOSE DATABASE statement before you create and start a transaction
log. The START DATABASE statement locks the database exclusively to
prevent access by other processes. If another process is using the database
(even if the database is only being read), the START DATABASE statement
fails.
The database remains locked after the START DATABASE statement executes.
When you are satisfied that the database is ready to use, execute the CLOSE
DATABASE statement to remove the exclusive lock. Reopen the database with
the DATABASE statement.
MODE ANSI Keyword
ANSI
Use the MODE ANSI keyword to make a database ANSI compliant. An
ANSI-compliant database conforms to different transaction-processing and
object-naming conventions than does a database that is not ANSI compliant.
The following example starts an ANSI-compliant database that is named
stores7:
START DATABASE stores7
WITH LOG IN '/u/myname/stores7.log' MODE ANSI
♦
Transaction Log Name Change
You must issue a START DATABASE statement immediately before you back
up the database if you plan to change the name or the location of the transaction log. Specify the new path to the transaction log in the START
DATABASE statement.
Stopping Logging
If you issue the START DATABASE statement with the WITH NO LOG clause
against a database that has logging, logging is turned off after the statement
is run. If you run the statement against a database that does not have logging,
no error is returned. This statement cannot be run on an ANSI-compliant
database.
1-582
Informix Guide to SQL: Syntax
START DATABASE
References
See the CREATE DATABASE and ROLLFORWARD DATABASE statements in this
manual.
In the Informix Guide to SQL: Tutorial, see the discussion of transaction
processing in Chapter 4 and Chapter 6.
SQL Statements 1-583
START VIOLATIONS TABLE
START VIOLATIONS TABLE
The START VIOLATIONS TABLE statement creates a violations table and a
diagnostics table for a specified target table. The database server associates
the violations and diagnostics tables with the target table by recording the
relationship among the three tables in the sysviolations system catalog table.
Syntax
+
USING
START VIOLATIONS TABLE FOR
tablename
,
MAX ROWS
violations
diagnostics
numrows
Element
Purpose
Restrictions
diagnostics
The name of the diagnostics
table to be associated with the
target table. The default name is
the name of the target table
followed by the characters _dia.
For further information on the
diagnostics table, see “Structure
of the Diagnostics Table” on
page 1-595.
The maximum number of rows
that can be inserted into the
diagnostics table when a single
statement (for example, INSERT
or SET) is executed on the target
table. There is no default value
for numrows. If you do not
specify a value for numrows,
there is no upper limit on the
number of rows that can be
inserted into the diagnostics
table when a single statement is
executed on the target table.
Whether you specify the name of Identifier, p. 1-723
the diagnostics table explicitly,
or the database server generates
the name implicitly, the name
cannot match the name of any
existing table in the database.
numrows
Syntax
You must specify an integer
Literal Number,
value in the range 1 to the
p. 1-752
maximum value of the INTEGER
data type.
(1 of 2)
1-584
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
Element
Purpose
table name
The name of the target table for
which a violations table and
diagnostics table are to be
created. There is no default
value.
violations
Restrictions
Syntax
If you do not include the USING Identifier, p. 1-723
clause in the statement, the name
of the target table must be less
than 15 characters. The target
table cannot have a violations
and diagnostics table associated
with it before you execute the
statement. The target table
cannot be a system catalog table.
The target table must be a local
table.
The name of the violations table Whether you specify the name of Identifier, p. 1-723
to be associated with the target the violations table explicitly, or
table. The default name is the
the database server generates
name of the target table followed the name implicitly, the name
by the characters _vio. For
cannot match the name of any
further information on the
existing table in the database.
violations table, see “Structure of
the Violations Table” on
page 1-586.
(2 of 2)
Usage
The START VIOLATIONS TABLE statement creates the special violations table
that holds rows that fail to satisfy constraints and unique indexes during
insert, update, and delete operations on target tables. This statement also
creates the special diagnostics table that contains information about the
integrity violations caused by each row in the violations table.
Relationship of START VIOLATIONS TABLE and SET Statements
The START VIOLATIONS TABLE statement is closely related to the SET
statement. If you use the SET statement to set the constraints or unique
indexes defined on a table to the filtering object mode, but you do not use the
START VIOLATIONS TABLE statement to start the violations and diagnostics
tables for this target table, any rows that violate a constraint or unique-index
requirement during an insert, update, or delete operation are not filtered out
to a violations table. Instead you receive an error message indicating that you
must start a violations table for the target table.
SQL Statements 1-585
START VIOLATIONS TABLE
Similarly, if you use the SET statement to set a disabled constraint or disabled
unique index to the enabled or filtering object mode, but you do not use the
START VIOLATIONS TABLE statement to start the violations and diagnostics
tables for the table on which the objects are defined, any existing rows in the
table that do not satisfy the constraint or unique-index requirement are not
filtered out to a violations table. If, in these cases, you want the ability to
identify existing rows that do not satisfy the constraint or unique-index
requirement, you must issue the START VIOLATIONS TABLE statement to start
the violations and diagnostics tables before you issue the SET statement to set
the objects to the enabled or filtering object mode.
Starting and Stopping the Violations and Diagnostics Tables
After you use a START VIOLATIONS TABLE statement to create an association
between a target table and the violations and diagnostics tables, the only way
to drop the association between the target table and the violations and
diagnostics tables is to issue a STOP VIOLATIONS TABLE statement for the
target table. For further information see the STOP VIOLATIONS TABLE
statement on page 1-602.
Examples of START VIOLATIONS TABLE Statements
The following examples show different ways to execute the START
VIOLATIONS TABLE statement.
Starting Violations and Diagnostics Tables Without Specifying Their Names
The following statement starts violations and diagnostics tables for the target
table named cust_subset. The violations table is named cust_subset_vio by
default, and the diagnostics table is named cust_subset_dia by default.
START VIOLATIONS TABLE FOR cust_subset
1-586
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
Starting Violations and Diagnostics Tables and Specifying Their Names
The following statement starts a violations and diagnostics table for the
target table named items. The USING clause assigns explicit names to the
violations and diagnostics tables. The violations table is to be named
exceptions, and the diagnostics table is to be named reasons.
START VIOLATIONS TABLE FOR items
USING exceptions, reasons
Specifying the Maximum Number of Rows in the Diagnostics Table
The following statement starts violations and diagnostics tables for the target
table named orders. The MAX ROWS clause specifies the maximum number
of rows that can be inserted into the diagnostics table when a single
statement, such as an INSERT or SET statement, is executed on the target table.
START VIOLATIONS TABLE FOR orders MAX ROWS 50000
Privileges Required for Starting Violations Tables
To start a violations and diagnostics table for a target table, you must meet
one of the following requirements:
■
You must have the DBA privilege on the database.
■
You must be the owner of the target table and have the Resource
privilege on the database.
■
You must have the Alter privilege on the target table and the
Resource privilege on the database.
Structure of the Violations Table
When you issue a START VIOLATIONS TABLE statement for a target table, the
violations table that the statement creates has a predefined structure. This
structure consists of the columns of the target table and three additional
columns.
SQL Statements 1-587
START VIOLATIONS TABLE
The following table shows the structure of the violations table.
Column Name
Type
Explanation
All columns of the target
table, in the same order
that they appear in the
target table
These columns of the
violations table match the
data type of the
corresponding columns
in the target table, except
that SERIAL columns in
the target table are
converted to INTEGER
data types in the
violations table.
The table definition of the target table is
reproduced in the violations table so that rows
that violate constraints or unique-index
requirements during insert, update, and delete
operations can be filtered to the violations table.
Users can examine these bad rows in the
violations table, analyze the related rows that
contain diagnostics information in the diagnostics
table, and take corrective actions.
informix_tupleid
SERIAL
This column contains the unique serial identifier
that is assigned to the nonconforming row.
informix_optype
CHAR(1)
This column indicates the type of operation that
caused this bad row. This column can have the
following values:
I = Insert
D = Delete
O = Update (with this row containing the
original values)
N = Update (with this row containing the
new values)
S = SET statement
informix_recowner
CHAR(8)
This column identifies the user who issued the
statement that created this bad row.
Relationship Between the Violations and Diagnostics Tables
Users can take advantage of the relationships among the target table, violations table, and diagnostics table to obtain complete diagnostic information
about rows that have caused data-integrity violations during INSERT,
DELETE, and UPDATE statements.
1-588
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
Each row of the violations table has at least one corresponding row in the
diagnostics table. The row in the violations table contains a copy of the row
in the target table for which a data-integrity violation was detected. The row
in the diagnostics table contains information about the nature of the dataintegrity violation caused by the bad row in the violations table. The row in
the violations table has a unique serial identifier in the informix_tupleid
column. The row in the diagnostics table has the same serial identifier in its
informix_tupleid column.
A given row in the violations table can have more than one corresponding
row in the diagnostics table. The multiple rows in the diagnostics table all
have the same serial identifier in their informix_tupleid column so that they
are all linked to the same row in the violations table. Multiple rows can exist
in the diagnostics table for the same row in the violations table because a bad
row in the violations table can cause more than one data-integrity violation.
For example, a bad row can violate a unique-index requirement for one
column, a not null constraint for another column, and a check constraint for
yet another column. In this case, the diagnostics table contains three rows for
the single bad row in the violations table. Each of these diagnostic rows
identifies a different data-integrity violation that the nonconforming row in
the violations table caused.
By joining the violations and diagnostics tables, the DBA or target table owner
can obtain complete diagnostic information about any or all bad rows in the
violations table. You can use SELECT statements to perform these joins
interactively, or you can write a program to perform them within
transactions.
SQL Statements 1-589
START VIOLATIONS TABLE
Initial Privileges on the Violations Table
When you issue the START VIOLATIONS TABLE statement to create the violations table, the database server uses the set of privileges granted on the target
table as a basis for granting privileges on the violations table. However, the
database server follows different rules when it grants each type of privilege.
The following table shows the initial set of privileges on the violations table.
The Privilege column lists the privilege. The Condition column explains the
conditions under which the database server grants the privilege to a user.
Privilege
Condition
Insert
The user has the Insert privilege on the violations table if the user has
any of the following privileges on the target table: the Insert privilege,
the Delete privilege, or the Update privilege on any column.
Delete
The user has the Delete privilege on the violations table if the user has
any of the following privileges on the target table: the Insert privilege,
the Delete privilege, or the Update privilege on any column.
Select
The user has the Select privilege on the informix_tupleid,
informix_optype, and informix_recowner columns of the violations
table if the user has the Select privilege on any column of the target
table.
The user has the Select privilege on any other column of the violations
table if the user has the Select privilege on the same column in the
target table.
Update
The user has the Update privilege on the informix_tupleid,
informix_optype, and informix_recowner columns of the violations
table if the user has the Update privilege on any column of the target
table.
The user has the Update privilege on any other column of the
violations table if the user has the Update privilege on the same
column in the target table.
(1 of 2)
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Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
Privilege
Condition
Index
The user has the Index privilege on the violations table if the user has
the Index privilege on the target table.
Alter
The Alter privilege is not granted on the violations table. (Users cannot
alter violations tables.)
References The References privilege is not granted on the violations table. (Users
cannot add referential constraints to violations tables.)
(2 of 2)
The following rules apply to ownership of the violations table and privileges
on the violations table:
■
When the violations table is created, the owner of the target table
becomes the owner of the violations table.
■
The owner of the violations table automatically receives all tablelevel privileges on the violations table, including the Alter and
References privileges. However, the database server prevents the
owner of the violations table from altering the violations table or
adding a referential constraint to the violations table.
■
You can use the GRANT and REVOKE statements to modify the initial
set of privileges on the violations table.
■
When you issue an INSERT, DELETE, or UPDATE statement on a target
table that has a filtering-mode unique index or constraint defined on
it, you must have the Insert privilege on the violations and
diagnostics tables.
If you do not have the Insert privilege on the violations and
diagnostics tables, the database server executes the INSERT, DELETE,
or UPDATE statement on the target table provided that you have the
necessary privileges on the target table. The database server does not
return an error concerning the lack of insert permission on the violations and diagnostics tables unless an integrity violation is detected
during the execution of the INSERT, DELETE, or UPDATE statement.
SQL Statements 1-591
START VIOLATIONS TABLE
Similarly, when you issue a SET statement to set a disabled constraint
or disabled unique index to the enabled or filtering mode, and a
violations table and diagnostics table exist for the target table, you
must have the Insert privilege on the violations and diagnostics
tables.
If you do not have the Insert privilege on the violations and
diagnostics tables, the database server executes the SET statement
provided that you have the necessary privileges on the target table.
The database server does not return an error concerning the lack of
insert permission on the violations and diagnostics tables unless an
integrity violation is detected during the execution of the SET
statement.
■
The grantor of the initial set of privileges on the violations table is the
same as the grantor of the privileges on the target table. For example,
if the user henry has been granted the Insert privilege on the target
table by both the user jill and the user albert, the Insert privilege on
the violations table is granted to user henry both by user jill and by
user albert.
■
Once a violations table has been started for a target table, revoking a
privilege on the target table from a user does not automatically
revoke the same privilege on the violations table from that user.
Instead you must explicitly revoke the privilege on the violations
table from the user.
■
If you have fragment-level privileges on the target table, you have
the corresponding fragment-level privileges on the violations table.
Example of Privileges on the Violations Table
The following example illustrates how the initial set of privileges on a violations table is derived from the current set of privileges on the target table.
For example, assume that we have created a table named cust_subset and
that this table consists of the following columns: ssn (customer’s social
security number), fname (customer’s first name), lname (customer’s last
name), and city (city in which the customer lives).
1-592
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
The following set of privileges exists on the cust_subset table:
■
User alvin is the owner of the table.
■
User barbara has the Insert and Index privileges on the table. She
also has the Select privilege on the ssn and lname columns.
■
User carrie has the Update privilege on the city column. She also has
the Select privilege on the ssn column.
■
User danny has the Alter privilege on the table.
Now user alvin starts a violations table named cust_subset_viols and a
diagnostics table named cust_subset_diags for the cust_subset table, as
follows:
START VIOLATIONS TABLE FOR cust_subset
USING cust_subset_viols, cust_subset_diags
The database server grants the following set of initial privileges on the
cust_subset_viols violations table:
■
User alvin is the owner of the violations table, so he has all tablelevel privileges on the table.
■
User barbara has the Insert, Delete, and Index privileges on the
violations table. She also has the Select privilege on the following
columns of the violations table: the ssn column, the lname column,
the informix_tupleid column, the informix_optype column, and the
informix_recowner column.
■
User carrie has the Insert and Delete privileges on the violations
table. She has the Update privilege on the following columns of the
violations table: the city column, the informix_tupleid column, the
informix_optype column, and the informix_recowner column. She
has the Select privilege on the following columns of the violations
table: the ssn column, the informix_tupleid column, the
informix_optype column, and the informix_recowner column.
■
User danny has no privileges on the violations table.
SQL Statements 1-593
START VIOLATIONS TABLE
Using the Violations Table
The following rules concern the structure and use of the violations table:
1-594
■
Every pair of update rows in the violations table has the same value
in the informix_tupleid column to indicate that both rows refer to
the same row in the target table.
■
If the target table has columns named informix_tupleid,
informix_optype, or informix_recowner, the database server
attempts to generate alternative names for these columns in the
violations table by appending a digit to the end of the column name
(for example, informix_tupleid1). If this attempt fails, the database
server returns an error, and the violations table is not started for the
target table.
■
When a table functions as a violations table, it cannot have triggers
or constraints defined on it.
■
When a table functions as a violations table, users can create indexes
on the table, even though the existence of an index affects performance. Unique indexes on the violations table cannot be set to the
filtering object mode.
■
If a target table has a violations and diagnostics table associated with
it, dropping the target table in cascade mode (the default mode)
causes the violations and diagnostics tables to be dropped also. If the
target table is dropped in the restricted mode, the existence of the
violations and diagnostics tables causes the DROP TABLE statement
to fail.
■
Once a violations table is started for a target table, you cannot use the
ALTER TABLE statement to add, modify, or drop columns in the target
table, violations table, or diagnostics table. Before you can alter any
of these tables, you must issue a STOP TABLE VIOLATIONS statement
for the target table.
■
The database server does not clear out the contents of the violations
table before or after it uses the violations table during an Insert,
Update, Delete, or Set operation.
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
■
If a target table has a filtering-mode constraint or unique index
defined on it and a violations table associated with it, users cannot
insert into the target table by selecting from the violations table.
Before you insert rows into the target table by selecting from the
violations table, you must take one of the following steps:
❑
You can set the object mode of the constraint or unique index to
the enabled or disabled object mode.
❑
You can issue a STOP VIOLATIONS TABLE statement for the target
table.
If it is inconvenient to take either of these steps, but you still want to
copy records from the violations table into the target table, a third
option is to select from the violations table into a temporary table and
then insert the contents of the temporary table into the target table.
■
If the target table that is specified in the START VIOLATIONS TABLE
statement is fragmented, the violations table has the same fragmentation strategy as the target table. Each fragment of the violations
table is stored in the same dbspace as the corresponding fragment of
the target table.
■
If the target table specified in the START VIOLATIONS TABLE
statement is not fragmented, the database server places the violations table in the same dbspace as the target table.
■
If the target table has blob columns, blobs in the violations table are
created in the same blob space as the blobs in the target table.
Example of a Violations Table
To start a violations and diagnostics table for the target table named customer
in the stores7 demonstration database, enter the following statement:
START VIOLATIONS TABLE FOR customer
SQL Statements 1-595
START VIOLATIONS TABLE
Because your START VIOLATIONS statement does not include a USING clause,
the violations table is named customer_vio by default. The customer_vio
table includes the following columns:
customer_num
fname
lname
company
address1
address2
city
state
zipcode
phone
informix_tupleid
informix_optype
informix_recowner
The customer_vio table has the same table definition as the customer table
except that the customer_vio table has three additional columns that contain
information about the operation that caused the bad row.
Structure of the Diagnostics Table
When you issue a START VIOLATIONS TABLE statement for a target table, the
diagnostics table that the statement creates has a predefined structure. This
structure is independent of the structure of the target table.
The following table shows the structure of the diagnostics table.
Column Name
Type
Explanation
informix_tupleid
INTEGER
This column in the diagnostics table implicitly
refers to the values in the informix_tupleid
column in the violations table. However, this
relationship is not declared as a foreign-key to
primary-key relationship.
objtype
CHAR(1)
This column identifies the type of the violation.
This column can have the following values.
C = Constraint violation
I = Unique-index violation
(1 of 2)
1-596
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
Column Name
Type
Explanation
objowner
CHAR(8)
This column identifies the owner of the constraint
or index for which an integrity violation was
detected.
objname
CHAR(18)
This column contains the name of the constraint
or index for which an integrity violation was
detected.
(2 of 2)
Initial Privileges on the Diagnostics Table
When the START VIOLATIONS TABLE statement creates the diagnostics table,
the database server uses the set of privileges granted on the target table as a
basis for granting privileges on the diagnostics table. However, the database
server follows different rules when it grants each type of privilege.
The following table shows the initial set of privileges on the diagnostics table.
The Privilege column lists the privilege. The Condition column explains the
conditions under which the database server grants the privilege to a user.
Privilege
Condition
Insert
The user has the Insert privilege on the diagnostics table if the user has
any of the following privileges on the target table: the Insert privilege,
the Delete privilege, or the Update privilege on any column.
Delete
The user has the Delete privilege on the diagnostics table if the user has
any of the following privileges on the target table: the Insert privilege,
the Delete privilege, or the Update privilege on any column.
Select
The user has the Select privilege on the diagnostics table if the user has
the Select privilege on any column in the target table.
Update
The user has the Update privilege on the diagnostics table if the user
has the Update privilege on any column in the target table.
(1 of 2)
SQL Statements 1-597
START VIOLATIONS TABLE
Privilege
Condition
Index
The user has the Index privilege on the diagnostics table if the user has
the Index privilege on the target table.
Alter
The Alter privilege is not granted on the diagnostics table. (Users
cannot alter diagnostics tables.)
References The References privilege is not granted on the diagnostics table. (Users
cannot add referential constraints to diagnostics tables.)
(2 of 2)
The following rules concern privileges on the diagnostics table:
■
When the diagnostics table is created, the owner of the target table
becomes the owner of the diagnostics table.
■
The owner of the diagnostics table automatically receives all tablelevel privileges on the diagnostics table, including the Alter and
References privileges. However, the database server prevents the
owner of the diagnostics table from altering the diagnostics table or
adding a referential constraint to the diagnostics table.
■
You can use the GRANT and REVOKE statements to modify the initial
set of privileges on the diagnostics table.
■
When you issue an INSERT, DELETE, or UPDATE statement on a target
table that has a filtering-mode unique index or constraint defined on
it, you must have the Insert privilege on the violations and
diagnostics tables.
If you do not have the Insert privilege on the violations and
diagnostics tables, the database server executes the INSERT, DELETE,
or UPDATE statement on the target table provided that you have the
necessary privileges on the target table. The database server does not
return an error concerning the lack of insert permission on the violations and diagnostics tables unless an integrity violation is detected
during the execution of the INSERT, DELETE, or UPDATE statement.
Similarly, when you issue a SET statement to set a disabled constraint
or disabled unique index to the enabled or filtering mode, and a
violations table and diagnostics table exist for the target table, you
must have the Insert privilege on the violations and diagnostics
tables.
1-598
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
If you do not have the Insert privilege on the violations and
diagnostics tables, the database server executes the SET statement
provided that you have the necessary privileges on the target table.
The database server does not return an error concerning the lack of
insert permission on the violations and diagnostics tables unless an
integrity violation is detected during the execution of the SET
statement.
■
The grantor of the initial set of privileges on the diagnostics table is
the same as the grantor of the privileges on the target table. For
example, if the user jenny has been granted the Insert privilege on
the target table by both the user wayne and the user laurie, both user
wayne and user laurie grant the Insert privilege on the diagnostics
table to user jenny.
■
Once a diagnostics table has been started for a target table, revoking
a privilege on the target table from a user does not automatically
revoke the same privilege on the diagnostics table from that user.
Instead you must explicitly revoke the privilege on the diagnostics
table from the user.
■
If you have fragment-level privileges on the target table, you have
the corresponding table-level privileges on the diagnostics table.
Example of Privileges on the Diagnostics Table
The following example illustrates how the initial set of privileges on a
diagnostics table is derived from the current set of privileges on the target
table.
For example, assume that there is a table called cust_subset and that this
table consists of the following columns: ssn (customer’s social security
number), fname (customer’s first name), lname (customer’s last name), and
city (city in which the customer lives).
The following set of privileges exists on the cust_subset table:
■
User alvin is the owner of the table.
■
User barbara has the Insert and Index privileges on the table. She
also has the Select privilege on the ssn and lname columns.
SQL Statements 1-599
START VIOLATIONS TABLE
■
User carrie has the Update privilege on the city column. She also has
the Select privilege on the ssn column.
■
User danny has the Alter privilege on the table.
Now user alvin starts a violations table named cust_subset_viols and a
diagnostics table named cust_subset_diags for the cust_subset table, as
follows:
START VIOLATIONS TABLE FOR cust_subset
USING cust_subset_viols, cust_subset_diags
The database server grants the following set of initial privileges on the
cust_subset_diags diagnostics table:
■
User alvin is the owner of the diagnostics table, so he has all tablelevel privileges on the table.
■
User barbara has the Insert, Delete, Select, and Index privileges on
the diagnostics table.
■
User carrie has the Insert, Delete, Select, and Update privileges on
the diagnostics table.
■
User danny has no privileges on the diagnostics table.
Using the Diagnostics Table
For information on the relationship between the diagnostics table and the
violations table, see “Relationship Between the Violations and Diagnostics
Tables” on page 1-587.
The following issues concern the structure and use of the diagnostics table:
1-600
■
The MAX ROWS clause of the START VIOLATIONS TABLE statement
sets a limit on the number of rows that can be inserted into the
diagnostics table when you execute a single statement, such as an
INSERT or SET statement, on the target table.
■
The MAX ROWS clause limits the number of rows only for operations
in which the table functions as a diagnostics table.
■
When a table functions as a diagnostics table, it cannot have triggers
or constraints defined on it.
Informix Guide to SQL: Syntax
START VIOLATIONS TABLE
■
When a table functions as a diagnostics table, users can create
indexes on the table, even though the existence of an index affects
performance. You cannot set unique indexes on the diagnostics table
to the filtering object mode.
■
If a target table has a violations and diagnostics table associated with
it, dropping the target table in the cascade mode (the default mode)
causes the violations and diagnostics tables to be dropped also. If the
target table is dropped in the restricted mode, the existence of the
violations and diagnostics tables causes the DROP TABLE statement
to fail.
■
Once a violations table is started for a target table, you cannot use the
ALTER TABLE statement to add, modify, or drop columns in the target
table, violations table, or diagnostics table. Before you can alter any
of these tables, you must issue a STOP TABLE VIOLATIONS statement
for the target table.
■
The database server does not clear out the contents of the diagnostics
table before or after it uses the diagnostics table during an Insert,
Update, Delete, or Set operation.
■
If the target table that is specified in the START VIOLATIONS TABLE
statement is fragmented, the diagnostics table is fragmented with a
round-robin strategy over the same dbspaces in which the target
table is fragmented.
Example of a Diagnostics Table
To start a violations and diagnostics table for the target table named stock in
the stores7 demonstration database, enter the following statement:
START VIOLATIONS TABLE FOR stock
Because your START VIOLATIONS TABLE statement does not include a USING
clause, the diagnostics table is named stock_dia by default. The stock_dia
table includes the following columns:
informix_tupleid
objtype
objowner
objname
SQL Statements 1-601
START VIOLATIONS TABLE
This list of columns shows an important difference between the diagnostics
table and violations table for a target table. Whereas the violations table has
a matching column for every column in the target table, the columns of the
diagnostics table do not match any columns in the target table. The
diagnostics table created by any START VIOLATIONS TABLE statement always
has the same columns with the same column names and data types.
References
See the STOP VIOLATIONS TABLE and SET statements in this manual.
For information on the system catalog tables that are associated with the
START VIOLATIONS TABLE statement, see the sysobjstate and sysviolations
tables in the Informix Guide to SQL: Reference.
1-602
Informix Guide to SQL: Syntax
STOP VIOLATIONS TABLE
STOP VIOLATIONS TABLE
The STOP VIOLATIONS TABLE statement drops the association between a
target table and the special violations and diagnostics tables.
Syntax
+
Element
table name
STOP VIOLATIONS TABLE FOR
Purpose
The name of the target table
whose association with the
violations and diagnostics table
is to be dropped. There is no
default value.
tablename
Restrictions
Syntax
The target table must have a
Identifier, p. 1-723
violations and diagnostics table
associated with it before you can
execute the statement. The target
table must be a local table.
Usage
The STOP VIOLATIONS TABLE statement drops the association between the
target table and the violations and diagnostics tables. After you issue this
statement, the former violations and diagnostics tables continue to exist, but
they no longer function as violations and diagnostics tables for the target
table. They now have the status of regular database tables instead of violations and diagnostics tables for the target table. You must issue the DROP
TABLE statement to drop these two tables explicitly.
When Insert, Delete, and Update operations cause data-integrity violations
for rows of the target table, the nonconforming rows are no longer filtered to
the former violations table, and diagnostics information about the dataintegrity violations is not placed in the former diagnostics table.
SQL Statements 1-603
STOP VIOLATIONS TABLE
Example of Stopping a Violations and Diagnostics Table
Assume that a target table named cust_subset has an associated violations
table named cust_subset_vio and an associated diagnostics table named
cust_subset_dia. To drop the association between the target table and the
violations and diagnostics tables, enter the following statement:
STOP VIOLATIONS TABLE FOR cust_subset
Example of Dropping a Violations and Diagnostics Table
After you execute the STOP VIOLATIONS TABLE statement in the preceding
example, the cust_subset_vio and cust_subset_dia tables continue to exist,
but they are no longer associated with the cust_subset table. Instead they
now have the status of regular database tables. To drop these two tables, enter
the following statements:
DROP TABLE cust_subset_vio;
DROP TABLE cust_subset_dia;
Privileges Required for Stopping a Violations Table
To stop a violations and diagnostics table for a target table, you must meet
one of the following requirements:
■
You must have the DBA privilege on the database.
■
You must be the owner of the target table and have the Resource
privilege on the database.
■
You must have the Alter privilege on the target table and the
Resource privilege on the database.
References
See the SET and START VIOLATIONS TABLE statements in this manual.
For information on the system catalog tables associated with the STOP
VIOLATIONS TABLE statement, see the sysobjstate and sysviolations tables
in the Informix Guide to SQL: Reference.
1-604
Informix Guide to SQL: Syntax
UNLOAD
UNLOAD
Use the UNLOAD statement to write the rows retrieved in a SELECT statement
to an operating-system file.
Syntax
DB
+
UNLOAD TO
SELECT
Statement
p. 1-459
'filename'
DELIMITER
Element
delimiter
filename
Purpose
A quoted string that identifies
the character to use as the
delimiter in the output file. The
delimiter is a character that
separates the data values in each
line of the output file. If you do
not specify a delimiter character,
the database server uses the
setting in the DBDELIMITER
environment variable. If
DBDELIMITER has not been set,
the default delimiter is the
vertical bar (|).
A quoted string that specifies the
pathname and filename of an
ASCII operating-system file. This
output file receives the selected
rows from the table during the
unload operation. The default
pathname for the output file is
the current directory.
'delimiter'
Restrictions
Syntax
You cannot use the following
Quoted String,
items as the delimiter character: p. 1-757
backslash (\), new-line character
(=CTRL-J), hexadecimal numbers
(0 to 9, a to f, A to F).
You can unload table data
containing VARCHAR or BLOB
data types to the output file, but
you should be aware of the
consequences. See “The
UNLOAD TO File” on
page 1-605 for further information.
Quoted String,
p. 1-757. The
pathname and
filename specified in
the quoted string
must conform to the
conventions of your
operating system.
SQL Statements 1-605
UNLOAD
Usage
To use the UNLOAD statement, you must have the Select privilege on all
columns selected in the SELECT statement. For information on database-level
and table-level privileges, see the GRANT statement on page 1-340.
The SELECT statement can consist of a literal SELECT statement or the name
of a character variable that contains a SELECT statement. (See the SELECT
statement on page 1-459.)
The UNLOAD TO File
The UNLOAD TO file contains the selected rows retrieved from the table. You
can use the UNLOAD TO file as the LOAD FROM file in a LOAD statement.
The following table shows types of data and their output format for an
UNLOAD statement in DB-Access (when DB-Access uses the default locale,
U.S. English).
Data Type
Output Format
character
If a character field contains the delimiter character,
Informix products automatically escape it with a backslash
(\) to prevent interpretation as a special character. (If you
use a LOAD statement to insert the rows into a table,
backslashes are automatically stripped.) Trailing blanks are
automatically clipped.
date
DATE values are represented as mm/dd/yyyy, where mm is
the month (January = 1, and so on), dd is the day, and yyyy
is the year. If you have set the GL_DATE or DBDATE
environment variable, the UNLOAD statement uses the
specified date format for DATE values. See Chapter 2 of the
Guide to GLS Functionality for more information about these
environment variables.
MONEY
MONEY values are unloaded with no leading currency
symbol. They use the comma (,) as the thousands separator
and the period as the decimal separator. If you have set the
DBMONEY environment variable, the UNLOAD statement
uses the specified currency format for MONEY values. See
Chapter 2 of the Guide to GLS Functionality for more information about this environment variable.
(1 of 2)
1-606
Informix Guide to SQL: Syntax
UNLOAD
Data Type
Output Format
NULL
NULL columns are unloaded by placing no characters
between the delimiters.
number
Number data types are displayed with no leading blanks.
INTEGER or SMALLINT zero are represented as 0, and
FLOAT, SMALLFLOAT, DECIMAL, or MONEY zero are represented as 0.00.
time
DATETIME and INTERVAL values are represented in
character form, showing only their field digits and delimiters. No type specification or qualifiers are included in the
output. The following pattern is used: yyyy-mm-dd
hh:mi:ss.fff, omitting fields that are not part of the data. If
you have set the GL_DATETIME or DBTIME environment
variable, the UNLOAD statement uses the specified format
for DATETIME values. See Chapter 2 of the Guide to GLS
Functionality for more information on these environment
variables.
(2 of 2)
GLS
If you are using a nondefault locale, the formats of DATE, DATETIME, MONEY,
and numeric column values in the UNLOAD TO file are determined by the
formats that the locale supports for these data types. For more information,
see Chapter 3 of the Guide to GLS Functionality. ♦
Do not use the backslash (\) as a field separator or UNLOAD delimiter. It
serves as an escape character to inform the UNLOAD command that the next
character is to be interpreted as part of the data.
If you are unloading files containing VARCHAR or BLOB data types, note the
following information:
■
BYTE items are written in hexadecimal dump format with no added
spaces or new lines. Consequently, the logical length of an unloaded
file that contains BYTE items can be very long and very difficult to
print or edit.
■
Trailing blanks are retained in VARCHAR fields.
■
Do not use the following characters as delimiters in the UNLOAD TO
file: 0 to 9, a to f, A to F, new-line character, or backslash.
SQL Statements 1-607
UNLOAD
If you are unloading files that contain BLOB data types, blobs smaller than
10 kilobytes are stored temporarily in memory. You can adjust the 10-kilobyte
setting to a larger setting with the DBBLOBBUF environment variable. Blobs
larger than the default or the setting of the DBBLOBBUF environment
variable are stored in a temporary file. For additional information about the
DBBLOBBUF environment variable, see the Informix Guide to SQL: Reference.
The following statement unloads rows from the customer table where the
value of customer_num is greater than or equal to 138, and puts them in a
file named cust_file:
UNLOAD TO 'cust_file' DELIMITER '!'
SELECT * FROM customer WHERE customer_num> = 138
The output file, cust_file, appears as shown in the following example:
138!Jeffery!Padgett!Wheel Thrills!3450 El Camino!Suite
10!Palo Alto!CA!94306!!
139!Linda!Lane!Palo Alto Bicycles!2344 University!!Palo
Alto!CA!94301!(415)323-5400
DELIMITER Clause
Use the DELIMITER clause to identify the delimiter that separates the data
contained in each column in a row in the output file. If you omit this clause,
DB-Access checks the DBDELIMITER environment variable.
If DBDELIMITER has not been set, the default delimiter is the vertical bar (|).
See Chapter 4 of the Informix Guide to SQL: Reference for information about
setting the DBDELIMITER environment variable.
You can specify the TAB (= CTRL-I) or <blank> (= ASCII 32) as the delimiter
symbol. You cannot use the following as the delimiter symbol:
1-608
■
Backslash (\)
■
New-line character (= CTRL-J)
■
Hexadecimal numbers (0 to 9, a to f, A to F)
Informix Guide to SQL: Syntax
UNLOAD
The following statement specifies the semicolon (;) as the delimiter character:
UNLOAD TO 'cust.out' DELIMITER ';'
SELECT fname, lname, company, city
FROM customer
References
See the LOAD and SELECT statements in this manual.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
UNLOAD statement
In the Informix Migration Guide, see the task-oriented discussion of the
UNLOAD statement and other utilities for moving data.
SQL Statements 1-609
UNLOCK TABLE
UNLOCK TABLE
Use the UNLOCK TABLE statement in a database without transactions to
unlock a table that you previously locked with the LOCK TABLE statement.
Syntax
+
UNLOCK TABLE
Table
Name
p. 1-768
Synonym
Name
p. 1-766
Usage
You can lock a table if you own the table or if you have the Select privileges
on the table, either from a direct grant or from a grant to public. You can only
unlock a table that you locked. You cannot unlock a table that another process
locked. Only one lock can apply to a table at a time.
The table name either is the name of the table you are unlocking or a synonym
for the table. Do not specify a view or a synonym of a view.
To change the lock mode of a table in a database without transactions, use the
UNLOCK TABLE statement to unlock the table, then issue a new LOCK TABLE
statement.
The UNLOCK TABLE statement fails if it is issued within a transaction. Table
locks set within a transaction are released automatically when the transaction
completes.
ANSI
1-610
You should not issue an UNLOCK TABLE statement within an ANSI-compliant
database. The UNLOCK TABLE statement fails if it is issued within a transaction, and a transaction is always in effect in an ANSI-compliant database. ♦
Informix Guide to SQL: Syntax
UNLOCK TABLE
References
See the COMMIT WORK, ROLLBACK WORK, and LOCK TABLE statements in
this manual.
SQL Statements 1-611
UPDATE
UPDATE
Use the UPDATE statement to change the values in one or more columns of
one or more rows in a table or view.
Syntax
UPDATE
Table
Name
p. 1-768
SET
SET Clause
p. 1-615
View
Name
p. 1-772
Synonym
Name
p. 1-766
Element
cursor id
1-612
Purpose
The name of the cursor to be
used by the UPDATE statement.
The current row of the active set
for this cursor is updated when
the UPDATE statement is
executed. See “WHERE
CURRENT OF Clause” on
page 1-619 for more information
on this parameter.
Informix Guide to SQL: Syntax
WHERE
ESQL
Condition
p. 1-643
SPL
CURRENT OF
cursor
id
Restrictions
Syntax
You cannot update a row with a Identifier, p. 1-723
cursor if that row includes
aggregates. The specified cursor
(as defined in the SELECT...FOR
UPDATE portion of a DECLARE
statement) can contain only
column names. If the cursor was
created without specifying
particular columns for updating,
you can update any column in a
subsequent UPDATE...WHERE
CURRENT OF statement. But if
the DECLARE statement that
created the cursor specified one
or more columns in the FOR
UPDATE clause, you can update
only those columns in a subsequent UPDATE...WHERE
CURRENT OF statement.
UPDATE
Usage
To update data in a table, you must either own the table or have the Update
privilege for the table (see the GRANT statement on page 1-340). To update
data in a view, you must have the Update privilege, and the view must meet
the requirements that are explained in “Updating Rows Through a View”
below.
If you omit the WHERE clause, all rows of the target table are updated.
If you are using effective checking, and the checking mode is set to
IMMEDIATE, all specified constraints are checked at the end of each UPDATE
statement. If the checking mode is set to DEFERRED, all specified constraints
are not checked until the transaction is committed.
DB
If you omit the WHERE clause and are in interactive mode, DB-Access does
not run the UPDATE statement until you confirm that you want to change all
rows. However, if the statement is in a command file, and you are running
from the command line, the statement executes immediately. ♦
Updating Rows Through a View
You can update data through a single-table view if you have the Update
privilege on the view (see the GRANT statement on page 1-340). To do this,
the defining SELECT statement can select from only one table, and it cannot
contain any of the following elements:
■
DISTINCT keyword
■
GROUP BY clause
■
Derived value (also called a virtual column)
■
Aggregate value
You can use data-integrity constraints to prevent users from updating values
in the underlying table when the update values do not fit the SELECT
statement that defined the view. For further information, refer to the WITH
CHECK OPTION discussion in the CREATE VIEW statement on page 1-224.
SQL Statements 1-613
UPDATE
Because duplicate rows can occur in a view even though the underlying table
has unique rows, be careful when you update a table through a view. For
example, if a view is defined on the items table and contains only the
order_num and total_price columns, and if two items from the same order
have the same total price, the view contains duplicate rows. In this case, if
you update one of the two duplicate total price values, you have no way to
know which item price is updated.
Important: You cannot update rows to a remote table through views with check
options.
Updating Rows in a Database Without Transactions
If you are updating rows in a database without transactions, you must take
explicit action to restore updated rows. For example, if the UPDATE statement
fails after updating some rows, the successfully updated rows remain in the
table. You cannot automatically recover from a failed update.
Updating Rows in a Database with Transactions
If you are updating rows in a database with transactions, and you are using
transactions, you can undo the update using the ROLLBACK WORK
statement. If you do not execute a BEGIN WORK statement before the update,
and the update fails, the database server automatically rolls back any
database modifications made since the beginning of the update.
ANSI
If you are updating rows in an ANSI-compliant database, transactions are
implicit, and all database modifications take place within a transaction. In
this case, if an UPDATE statement fails, you can use the ROLLBACK WORK
statement to undo the update.
If you are using INFORMIX-OnLine Dynamic Server, you are within an
explicit transaction, and the update fails, the database server automatically
undoes the effects of the update. ♦
1-614
Informix Guide to SQL: Syntax
UPDATE
Locking Considerations
If you are using an OnLine database server, when a row is selected with the
intent to update, the update process acquires an update lock. Update locks
permit other processes to read, or share, a row that is about to be updated but
do not let those processes update or delete it. Just before the update occurs,
the update process promotes the shared lock to an exclusive lock. An exclusive
lock prevents other processes from reading or modifying the contents of the
row until the lock is released.
INFORMIX-OnLine Dynamic Server allows only one update lock at a time on
a row or a page (the type of lock depends on the lock mode that is selected in
the CREATE TABLE or ALTER TABLE statements). An update process can
acquire an update lock on a row or a page that has a shared lock from another
process, but you cannot promote the update lock from shared to exclusive
(and the update cannot occur) until the other process releases its lock.
If the number of rows affected by a single update is very large, you can
exceed the limits placed on the maximum number of simultaneous locks. If
this occurs, you can reduce the number of transactions per UPDATE
statement, or you can lock the page (OnLine database servers only) or the
entire table before you execute the statement.
SE
Individual rows of a table are locked automatically when you execute an
UPDATE statement. ♦
SQL Statements 1-615
UPDATE
SET Clause
SET
Clause
,
column
name
=
Expression
(Subset)
p. 1-616
(
+
SELECT
Statement
(Subset)
p. 1-617
)
NULL
,
(
column
name
,
)
=
(
*
(
SELECT
Statement
(Subset)
p. 1-617
NULL
1-616
Informix Guide to SQL: Syntax
)
Expression
(Subset)
p. 1-616
)
UPDATE
Subset of SELECT Statements Allowed in the SET Clause
A SELECT statement used in a SET clause can return more than one column of
information in a row. However, the SELECT statement cannot return more
than one row of information in a table. For a complete description of syntax
and usage, refer to the SELECT statement on page 1-459.
Single Columns to Single Expressions
You can include any number of single-column to single-expressions in an
UPDATE statement.
The following examples illustrate the single-column to single-expression
form of the SET clause:
UPDATE customer
SET address1 = '1111 Alder Court',
city = 'Palo Alto',
zipcode = '94301'
WHERE customer_num = 103
UPDATE orders
SET ship_charge =
(SELECT SUM(total_price) * .07
FROM items
WHERE orders.order_num = items.order_num)
WHERE orders.order_num = 1001
UPDATE stock
SET unit_price = unit_price * 1.07
Updating a Column to NULL
You can use the NULL keyword to modify a column value when you use the
UPDATE statement. For a customer whose previous address required two
address lines but now requires only one, you would use the following entry:
UPDATE customer
SET address1 = '123 New Street',
SET address2 = null,
city = 'Palo Alto',
zipcode = '94303'
WHERE customer_num = 134
1-618
Informix Guide to SQL: Syntax
UPDATE
Multiple Columns Equal to Multiple Expressions
The SET clause offers the following options for listing a series of columns you
intend to update:
■
Explicitly list each column, placing commas between columns and
enclosing the set of columns in parentheses.
■
Implicitly list all columns in table name using the asterisk notation (*).
To complete the SET clause, you must list each expression explicitly, placing
commas between expressions and enclosing the set of expressions in parentheses. An expression list can include an <vk>SQL subquery that returns a
single row of multiple values as long as the number of columns named,
explicitly or implicitly, equals the number of values produced by the
expression or expressions that follow the equal sign.
The following examples illustrate the multiple-column to multipleexpression form of the SET clause:
UPDATE customer
SET (fname, lname) = ('John', 'Doe')
WHERE customer_num = 101
UPDATE manufact
SET * = ('HNT', 'Hunter')
WHERE manu_code = 'ANZ'
UPDATE items
SET (stock_num, manu_code, quantity) =
( (SELECT stock_num, manu_code FROM stock
WHERE description = 'baseball'), 2)
WHERE item_num = 1 AND order_num = 1001
UPDATE table1
SET (col1, col2, col3) =
((SELECT MIN (ship_charge),
MAX (ship_charge) FROM orders),
'07/01/1993')
WHERE col4 = 1001
SQL Statements 1-619
UPDATE
WHERE Clause
The WHERE clause lets you limit the rows that you want to update. If you
omit the WHERE clause, every row in the table is updated.
The WHERE clause consists of a standard search condition. (For more
information, see the SELECT statement on page 1-459). The following
example illustrates a WHERE condition within an UPDATE statement. In this
example, the statement updates three columns (state, zipcode, and phone) in
each row of the customer table that has a corresponding entry in a table of
new addresses called new_address.
UPDATE customer
SET (state, zipcode, phone) =
((SELECT state, zipcode, phone FROM new_address N
WHERE N.cust_num =
customer.customer_num))
WHERE customer_num IN
(SELECT cust_num FROM new_address)
When you use the UPDATE statement with the WHERE clause, and no rows
are updated, the SQLNOTFOUND value is 100 in ANSI-compliant databases
and 0 in databases that are not ANSI compliant. If the UPDATE ... WHERE ... is
a part of a multistatement prepare, and no rows are returned, the
SQLNOTFOUND value is 100 for ANSI-compliant databases and databases
that are not ANSI compliant.
WHERE CURRENT OF Clause
ESQL
1-620
You can use the CURRENT OF keyword to update the current row of the active
set of a cursor. However, you cannot update a row with a cursor if that row
includes aggregates. The cursor named in the CURRENT OF clause can only
contain column names. The UPDATE statement does not advance the cursor
to the next row, so the current row position remains unchanged.
Informix Guide to SQL: Syntax
UPDATE
You can restrict the effect of the CURRENT OF keyword if you associate the
UPDATE statement with a cursor that was created with the FOR UPDATE
keyword. (See the DECLARE statement on page 1-234.) If you created the
cursor without specifying any columns for updating, you can update any
column in a subsequent UPDATE...WHERE CURRENT OF statement. However,
if the DECLARE statement that created the cursor specified one or more
columns in the FOR UPDATE clause, you are restricted to updating only those
columns in a subsequent UPDATE...WHERE CURRENT OF statement. The
advantage to specifying columns in the FOR UPDATE clause of a DECLARE
statement is speed. INFORMIX-SE and INFORMIX-OnLine Dynamic Server can
usually perform updates more quickly if columns are specified in the
DECLARE statement. ♦
The following INFORMIX-ESQL/C example illustrates the WHERE CURRENT
OF form of the WHERE clause. In this example, updates are performed on a
range of customers who receive 10-percent discounts (assume that a new
column, discount, is added to the customer table). The UPDATE statement is
prepared outside the WHILE loop to ensure that parsing is done only once.
(For more information, see the PREPARE statement on page 1-402.)
char answer [1] = 'y';
SQL Statements 1-621
UPDATE
}
printf("\nUpdate %.10s %.10s (y/n)?", fname, lname);
if (answer = getch() == 'y')
EXEC SQL execute u;
EXEC SQL close x;
}
Tip: You can use an update cursor to perform updates that are not possible with the
UPDATE statement. An update cursor is a sequential cursor that is associated with
a SELECT statement, which is declared with the FOR UPDATE keyword. For more
information on the update cursor, see page 1-239.
References
See the DECLARE, INSERT, OPEN, and SELECT statements in this manual.
In the Informix Guide to SQL: Tutorial, see the discussion of the UPDATE
statement in Chapter 6.
In the Guide to GLS Functionality, see the discussion of the GLS aspects of the
UPDATE statement.
1-622
Informix Guide to SQL: Syntax
UPDATE STATISTICS
UPDATE STATISTICS
Use the UPDATE STATISTICS statement to update system catalog tables with
information used to determine optimal query plans. In addition, you can use
the UPDATE STATISTICS statement to force stored procedures to be
reoptimized. If you are upgrading to a new version of the database server,
you can use UPDATE STATISTICS to convert table indexes to the format that
the new database server uses.
SQL Statements 1-623
UPDATE STATISTICS
Syntax
UPDATE STATISTICS
+
FOR PROCEDURE
Procedure
Name
p. 1-754
LOW
Table
Name
1-768
FOR
TABLE
DROP
DISTRIBUTIONS
,
column
name
(
Synonym
Name
p. 1-766
)
MEDIUM
FOR
TABLE
Table
Name
p. 1-768
RESOLUTION
percent
,
(
Synonym
Name
p. 1-766
column
name
)
OL
conf
DISTRIBUTIONS ONLY
HIGH
FOR
TABLE
Synonym
Name
p. 1-766
1-624
RESOLUTION
Table
Name
p. 1-768
Informix Guide to SQL: Syntax
,
(
column
name
percent
OL
)
DISTRIBUTIONS ONLY
UPDATE STATISTICS
Element
column name
conf
percent
Purpose
The name of a column in the
specified table
Restrictions
The column must exist. If you
use the LOW keyword and want
the UPDATE STATISTICS
statement to do minimal work,
specify a column name that is
not part of an index. If you use
the MEDIUM or HIGH keywords,
column name cannot be a BYTE or
TEXT column.
The expected fraction of times
The minimum confidence level
that the sampling entailed by the is 0.80. The maximum confiMEDIUM keyword should
dence level is 0.99.
produce the same results as the
exact methods entailed by the
HIGH keyword. The default
confidence level is 0.95. See
“Specifying MEDIUM
Distributions” on page 1-628 for
further information on this
parameter.
The desired resolution in units of The minimum resolution
percent, so that 0.1 means the
possible for a table is 1/nrows,
data in a column is divided into where nrows is the number of
bins, each containing (on
rows in the table.
average) 0.1 percent of the data.
The default value of percent is 2.5
when the MEDIUM keyword is
used. The default value of
percent is 0.5 when the HIGH
keyword is used. See “Creating
Distributions for Columns” on
page 1-627 for further
information on this parameter.
Syntax
Identifier, p. 1-723
Literal Number,
p. 1-752
Literal Number,
p. 1-752
SQL Statements 1-625
UPDATE STATISTICS
Usage
When you issue an UPDATE STATISTICS statement, INFORMIX-OnLine
Dynamic Server recalculates the data in the systables, syscolumns,
sysindexes, and sysdistrib system catalog tables. The optimizer uses this
data to determine the best execution path for queries. The database server
does not update this statistical data automatically. Statistics are updated only
when you issue an UPDATE STATISTICS statement.
Using the UPDATE STATISTICS statement also updates the optimized
execution plans for procedures in the sysprocplan system catalog table. Each
time a procedure executes, the database server reoptimizes its execution plan
if any objects that are referenced in the procedure have changed.
The UPDATE STATISTICS statement requires a current database. If you omit
the FOR TABLE or FOR PROCEDURE clauses, statistics are updated for every
table and procedure in the current database, including the system tables.
If you use UPDATE STATISTICS ... FOR TABLE without a table name, the
statistics for all tables, including temporary tables, in the current database are
updated. If you use the FOR PROCEDURE keyword without a procedure
name, the statistics for all stored procedures in the current database are
updated.
You cannot update the statistics used by the optimizer for a table or
procedure that is external to the current database.
SE
With INFORMIX-SE, UPDATE STATISTICS does not update rows in the
sysindexes table; when you issue an UPDATE STATISTICS statement,
INFORMIX-SE recalculates only the data in the systables and, when
requested, the sysdistrib system catalog tables. ♦
Examining Index Pages
The UPDATE STATISTICS statement reads through index pages in order to
compute statistics for the query optimizer. In addition, the statement also
looks for pages that have the delete flag marked as one. If pages are found
with the delete flag marked as one, the keys so marked are removed from the
btree cleaner list. This is particularly useful if a system crash causes the btree
cleaner list to be lost (because it is in shared memory). To remove those items,
run the UPDATE STATISTICS statement. For information on the btree cleaner
list, see the INFORMIX-OnLine Dynamic Server Administrator’s Guide.
1-626
Informix Guide to SQL: Syntax
UPDATE STATISTICS
When to Update Statistics
Update the statistics when you perform extensive modifications to a table or
when changes are made to tables that are used by one or more procedures,
and you do not want the database server to reoptimize the procedure at
execution time.
If your application makes many modifications to the data in a particular
table, update the system catalog table data for that table routinely with the
UPDATE STATISTICS statement to improve the efficiency of queries. Many is
relative to the resolution of the distributions. In addition, if the data changes
do not change the distribution of column values, you do not need to execute
UPDATE STATISTICS again.
Using UPDATE STATISTICS when Upgrading the Database
Server
When you are upgrading a database for use with a newer database server,
you can use the UPDATE STATISTICS statement to convert the indexes to the
form that the newer server uses. You can choose to convert the indexes table
by table or for the entire database at one time. You should follow the
conversion guidelines that are outlined in the Informix Migration Guide or the
INFORMIX-SE Administrator’s Guide.When you use the UPDATE STATISTICS
statement to convert the indexes for use with a newer database server, the
indexes are implicitly dropped and re-created. Upgrading is the only time
that an UPDATE STATISTICS statement causes implicit dropping and recreation of table indexes.
Specifying the LOW Keyword
If you use the LOW keyword, or if you specify no keyword, the smallest
amount of information is gathered about the column. The data in the
systables, syscolumns, and sysindexes tables is updated. No information is
put into the sysdistrib system catalog table. If data already exists in the
sysdistrib system catalog table when you run an UPDATE STATISTICS (LOW)
statement, the distribution data remains intact unless the DROP
DISTRIBUTIONS option is used. If the DROP DISTRIBUTIONS option is
specified, but no table name is specified, all the distribution information is
removed.
SQL Statements 1-627
UPDATE STATISTICS
The UPDATE STATISTICS (LOW) statement updates table, row, and page
counts as well as index and column statistics for specified columns. If you
want the UPDATE STATISTICS statement to do minimal work, specify a
column that is not part of an index.
The following example updates statistics on the customer_num column of
the customer table. All distributions associated with the customer table
remain intact, even those that already exist on the customer_num column.
UPDATE STATISTICS LOW FOR TABLE customer (customer_num)
Dropping Data with the DROP DISTRIBUTIONS Clause
If you want to drop distribution data for some or all the columns that are
already defined in the sysdistrib table, but you want to update the statistics
with the LOW option for the rest of the columns in the table, you can use the
DROP DISTRIBUTIONS clause. If you specify the DROP DISTRIBUTIONS
keyword, all distribution information that exists for the column specified in
the UPDATE STATISTICS statement drops. If no columns are specified, all the
distributions for that table are removed.
You must have the DBA privileges or be the owner of the table in order to
drop distributions.
The following example shows how to remove distributions for the
customer_num column in the customer table:
UPDATE STATISTICS LOW
FOR TABLE customer (customer_num) DROP DISTRIBUTIONS
Creating Distributions for Columns
Distributions are a mapping of the data in the column into a carefully chosen
set of the column values. The contents of the column are examined and
divided into bins, which represent a percentage of data. For example, a bin
might hold 2 percent of the data; 50 bins would hold all the data. You can set
the width of the bin with the RESOLUTION percent parameter.
This organization of column values into bins is called the distribution (for
that column). The optimizer examines distributions of columns that are referenced in a WHERE clause to estimate the effect of a WHERE clause on the data.
1-628
Informix Guide to SQL: Syntax
UPDATE STATISTICS
You cannot create distributions for TEXT or BYTE columns. If you include a
TEXT or BYTE column in an UPDATE STATISTICS statement that specifies
medium or high distributions, no distributions are created for those columns.
Distributions are constructed for other columns in the list, and the statement
does not return an error.
You must have the DBA privilege or be the owner of the table in order to
create high or medium distributions.
Specifying High Distributions
If you use the HIGH keyword, the constructed distribution is exact, rather
than statistically significant. Because of the time required to gather the information, you should use high distributions for specific tables or even columns
rather than across the database. For very large tables, the database server
may scan the data once for each column. The amount of space designated by
the DBUPSPACE environment variable determines the number of times the
table is scanned. For information about DBUPSPACE, see Chapter 4 of the
Informix Guide to SQL: Reference.
If you do not specify a RESOLUTION clause, the default percentage is
0.5 percent.
Specifying MEDIUM Distributions
If you use the MEDIUM keyword, the data for the distributions is obtained by
sampling. Because the data obtained by sampling is usually much smaller
than the actual number of rows, the time required to construct medium
distributions is less than the time required for high mode. Medium
distributions require at least one scan of the table, so the creation of medium
distributions executes more slowly than the creation of low distributions.
If you do not specify a RESOLUTION clause, the default percentage is
2.5 percent. If you do not specify a value for conf, the default confidence is
0.95. This can be roughly interpreted as meaning that 95 percent of the time,
the estimate is equivalent to using high distributions.
SQL Statements 1-629
UPDATE STATISTICS
Specifying DISTRIBUTIONS ONLY to Suppress Index Information
When you specify the MEDIUM or HIGH keywords, your UPDATE STATISTICS
statement performs the functions of the LOW keyword as well. The functionality of the LOW keyword consists of constructing table information and
index information for the specified objects. If you specify the DISTRIBUTIONS
ONLY option with the MEDIUM or HIGH keywords, you prevent the
construction of index information. However, table information is still
constructed for the specified objects when you specify the DISTRIBUTIONS
ONLY option. This information includes the number of pages used, the
number of rows, and fragment information.
The reasons for suppressing index information but not table information
with the DISTRIBUTIONS ONLY option are as follows:
■
The table information is required to construct accurate distributions.
■
The construction of index information can take a considerable
amount of time, but the construction of table information requires
very little time and very few system resources.
In the following example, the UPDATE STATISTICS statement gathers distributions information, index information, and table information for the
customer table:
UPDATE STATISTICS MEDIUM FOR TABLE customer
However, in the following example, only distributions information and table
information are gathered for the customer table. The DISTRIBUTIONS ONLY
option prevents the construction of index information.
UPDATE STATISTICS MEDIUM FOR TABLE customer
DISTRIBUTIONS ONLY
1-630
Informix Guide to SQL: Syntax
UPDATE STATISTICS
Recommended Procedure for Updating Statistics
Informix recommends the following procedure for giving the optimizer the
best possible information while incurring the lowest performance penalty:
1.
Run UPDATE STATISTICS in medium mode with the DISTRIBUTIONS
ONLY option for each table. (If you are the database owner or DBA,
and you want to gather statistics for the entire database, you can do
that with a single command instead.). The default parameters are
sufficient unless the table is very large. In this case, use a resolution
of 1.00 and a confidence level of 0.99.
2.
Run UPDATE STATISTICS in high mode for all columns that head an
index. For the fastest execution time of the UPDATE STATISTICS statement, you must execute one UPDATE STATISTICS statement in the
high mode for each such column. In a future release, Informix will
remove this limitation.
3.
For each multicolumn index, run UPDATE STATISTICS in low mode
for all its columns.
This procedure executes rapidly because it only constructs the indexinformation statistics once for each index.
Update Statistics and Temporary Tables
You can use UPDATE STATISTICS on temporary tables. You can explicitly
update the statistics for a temporary table or build distributions for a
temporary table by specifying the name of the table. If you build distributions on all of the tables in the database by using the FOR TABLE clause
without a specific table name, distributions will also be built on all the
temporary tables in your session.
References
In the INFORMIX-OnLine Dynamic Server Performance Guide, see the
discussion of UPDATE STATISTICS. In the Informix Migration Guide, see the
discussion of how to use the dbschema utility to view distributions created
with UPDATE STATISTICS.
SQL Statements 1-631
WHENEVER
WHENEVER
Use the WHENEVER statement to trap exceptions that occur during the
execution of <vk>SQL statements.
Syntax
ESQL
WHENEVER
SQLERROR
CONTINUE
+
GO TO
NOT FOUND
: label
GOTO
+
STOP
SQLWARNING
E/CO
CALL
ERROR
label
E/CO
function
name
+
PERFORM
Element
function name
Syntax
Function or
procedure name
must conform to
language-specific
rules for functions or
procedures.
label
Statement label to which
An ESQL/COBOL label must be a Label must conform
program control transfers when paragraph name or a procedure to language-specific
an exception occurs
name.
rules for statement
labels.
paragraph name Name of a paragraph of COBOL The paragraph to be executed
Paragraph name
code to be executed when an SQL must exist within the program. must conform to
statement generates an error
language-specific
rules for paragraph
names.
1-632
Purpose
Restrictions
Function or procedure that is
Function or procedure must
called when an exception occurs exist at compile time. A
procedure in COBOL is
equivalent to a function in C.
paragraph
name
Informix Guide to SQL: Syntax
WHENEVER
Type of Action
WHENEVER Keyword
For More Information
Transfer control to a specified label
GOTO
GO TO
page 1-636
Transfer control to a named function
or procedure
CALL
page 1-637
Transfer control to a specified COBOL
paragraph
PERFORM
(ESQL/COBOL only)
page 1-638
(2 of 2)
The Scope of WHENEVER
The ESQL preprocessor, not the database server, handles the interpretation of
the WHENEVER statement. When the preprocessor encounters a WHENEVER
statement in an ESQL source file, it inserts the appropriate code into the
preprocessed code after each <vk>SQL statement based on the exception and
the action that WHENEVER lists. The preprocessor defines the scope of a
WHENEVER statement as from the point that it encounters the statement in
the source module until it encounters one of the following conditions:
■
The next WHENEVER statement with the same exception condition
(SQLERROR, SQLWARNING, and NOT FOUND) in the same source
module
■
The end of the source module
Whichever condition the preprocessor encounters first as it sequentially
processes the source module marks the end of the scope of the WHENEVER
statement.
The following ESQL/C example program has three WHENEVER statements,
two of which are WHENEVER SQLERROR statements. Line 4 uses STOP with
SQLERROR to override the default CONTINUE action for errors. Line 8
specifies the CONTINUE keyword to return the handling of errors to the
default behavior. For all <vk>SQL statements between lines 4 and 8, the
preprocessor inserts code that checks for errors and halts program execution
if an error occurs. Therefore, any errors that the INSERT statement on line 6
generates cause the program to stop.
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Informix Guide to SQL: Syntax
WHENEVER
After line 8, the preprocessor does not insert code to check for errors after
<vk>SQL statements. Therefore, any errors that the INSERT statement (line
10), the SELECT statement (line 11), and DISCONNECT statement (line 12)
generate are ignored. However, the SELECT statement does not stop program
execution if it does not locate any rows; the WHENEVER statement on line 7
tells the program to continue if such an exception occurs.
1
2
main()
{
3
EXEC SQL connect to 'test';
4
EXEC SQL WHENEVER SQLERROR STOP;
5
6
printf("\n\nGoing to try first insert\n\n");
EXEC SQL insert into test_color values ('green');
7
8
EXEC SQL WHENEVER NOT FOUND CONTINUE;
EXEC SQL WHENEVER SQLERROR CONTINUE;
9
10
11
12
13
14
printf("\n\nGoing to try second insert\n\n");
EXEC SQL insert into test_color values ('blue');
EXEC SQL select paint_type from paint where color='red';
EXEC SQL disconnect all;
printf("\n\nProgram over\n\n");
}
SQLERROR Keyword
If you use the SQLERROR keyword, any <vk>SQL statement that encounters
an error is handled as the WHENEVER SQLERROR statement directs. If an
error occurs, the sqlcode variable is less than zero and the SQLSTATE variable
has a class code with a value greater than 02. The following table lists the
specification for the sqlcode variable for each product.
Product Name
Variable Name
ESQL/C
sqlca.sqlcode, SQLCODE
ESQL/COBOL
SQLCODE OF SQLCA
The following statement causes a program to stop execution if an <vk>SQL
error exists:
WHENEVER SQLERROR STOP
SQL Statements 1-635
WHENEVER
If you do not use any WHENEVER SQLERROR statements in a program, the
default for WHENEVER SQLERROR is CONTINUE.
SQLWARNING Keyword
If you use the SQLWARNING keyword, any <vk>SQL statement that
generates a warning is handled as the WHENEVER SQLWARNING statement
directs. If a warning occurs, the first field of the warning structure in SQLCA
is set to W, and the SQLSTATE variable has a class code of 01. The following
table lists the specification for the first field of the SQLCA warning structure
for each product.
Product Name
Variable Name
ESQL/C
sqlca.sqlwarn.sqlwarn0
ESQL/COBOL
SQLWARN1 OF SQLWARN OF SQLCA
In addition to setting the first field of the warning structure, a warning also
sets an additional field to W. The field that is set indicates the type of warning
that occurred. For more information, see the chapter on exception checking
in your <vk>SQL API manual.
The following statement causes a program to stop execution if a warning
condition exists:
WHENEVER SQLWARNING STOP
If you do not use any WHENEVER SQLWARNING statements in a program, the
default for WHENEVER SQLWARNING is CONTINUE.
NOT FOUND Keywords
If you use the NOT FOUND keywords, exception handling for SELECT and
FETCH statements is treated differently than for other <vk>SQL statements.
The NOT FOUND keyword checks for the following cases:
1-636
■
The End of Data condition: a FETCH statement that attempts to get a
row beyond the first or last row in the active set
■
The Not Found condition: a SELECT statement that returns no rows
Informix Guide to SQL: Syntax
WHENEVER
In each case, the sqlcode variable is set to 100, and the SQLSTATE variable
has a class code of 02. For the name of the sqlcode variable in each Informix
product, see the table in “SQLERROR Keyword” on page 1-634.
The following statement calls the no_rows() function each time the NOT
FOUND condition exists:
WHENEVER NOT FOUND CALL no_rows
If you do not use any WHENEVER NOT FOUND statements in a program, the
default for WHENEVER NOT FOUND is CONTINUE.
ERROR Keyword
E/CO
ERROR is a synonym for SQLERROR. For more information, see “SQLERROR
Keyword” on page 1-634. ♦
CONTINUE Keyword
Use the CONTINUE keyword to instruct the program to ignore the exception
and to continue execution at the next statement after the <vk>SQL statement.
The default action for all exceptions is CONTINUE. You can use this keyword
to turn off a previously specified option.
STOP Keyword
Use the STOP keyword to instruct the program to stop execution when the
specified exception occurs. The following statement halts execution of an
ESQL/C program each time that an <vk>SQL statement generates a warning:
EXEC SQL WHENEVER SQLWARNING STOP;
GOTO Keyword
Use the GOTO clause to transfer control to the statement that the label
identifies when a particular exception occurs. The GOTO keyword is the
ANSI-compliant syntax of the clause. The GO TO keywords are a non-ANSI
synonym for GOTO.
SQL Statements 1-637
WHENEVER
The following example shows a WHENEVER statement in INFORMIX-ESQL/C
code that transfers control to the label missing each time that the NOT
FOUND condition occurs:
query_data()
.
.
.
EXEC SQL WHENEVER NOT FOUND GO TO missing;
.
.
.
EXEC SQL fetch lname into :lname;
.
.
.
missing:
printf("No Customers Found\n");
.
.
.
You must define the labeled statement in each program block that contains
<vk>SQL statements. If your program contains more than one function, you
might need to include the labeled statement and its code in each function.
When the preprocessor reaches the function that does not contain the labeled
statement, it tries to insert the code associated with the labeled statement.
However, if you do not define this labeled statement within the function, the
preprocessor generates an error.
To correct this error, either put a labeled statement with the same label name
in each function, issue another WHENEVER statement to reset the error
condition, or use the CALL clause to call a separate function.
CALL Clause
Use the CALL clause to transfer program control to the named function or
procedure when a particular exception occurs. Do not include parentheses
after the function or procedure name. The following WHENEVER statement
causes the program to call the error_recovery() function if the program
detects an error:
EXEC SQL WHENEVER SQLERROR CALL error_recovery;
1-638
Informix Guide to SQL: Syntax
WHENEVER
When the named function completes, execution resumes at the next
statement after the line that is causing the error. If you want to halt execution
when an error occurs, include statements that terminate the program as part
of the named function.
Observe the following restrictions on the named function:
■
You cannot pass arguments to the named function nor can you return
values from the named function. If the named function needs
external information, use global variables or the GOTO clause of
WHENEVER to transfer control to a label that calls the named
function.
■
You cannot specify the name of a stored procedure as a named
function. To call a stored procedure, use the CALL clause to execute a
function that contains the EXECUTE PROCEDURE statement.
■
Make sure that all functions that the WHENEVER...CALL statement
affects can find a declaration of the named function.
PERFORM Keyword for COBOL
Use the PERFORM keyword to execute a paragraph of COBOL code. The
following example executes the COBOL paragraph ERR-CHK when an
<vk>SQL statement generates an error:
EXEC SQL WHENEVER ERROR PERFORM ERR-CHK END-EXEC.
References
See the EXECUTE PROCEDURE and FETCH statements in this manual.
See the chapter on exception checking and error checking in your SQL API
product manual.
SQL Statements 1-639
Segments
Segments
Segments are language elements, such as table names and expressions, that
occur repeatedly in the syntax diagrams for SQL and SPL statements. These
language elements are discussed separately in this section for the sake of
clarity, ease of use, and comprehensive treatment.
Whenever a segment occurs within the syntax diagram for an SQL or SPL
statement, the diagram references the description of the segment in this
section.
Scope of Segment Descriptions
The description of each segment includes the following information:
■
A brief introduction that explains the purpose of the segment
■
A syntax diagram that shows how to enter the segment correctly
■
A syntax table that explains each input parameter in the syntax
diagram
■
Rules of usage, including examples that illustrate these rules
If a segment consists of multiple parts, the segment description provides the
same set of information for each part. Each segment description concludes
with references to related information in this manual and other manuals.
Use of Segment Descriptions
The syntax diagram within each segment description is not a standalone
diagram. Instead it is a subdiagram that is subordinate to the syntax diagram
for an SQL or SPL statement. A reference box in the syntax diagram for the
statement refers to this subdiagram by providing the name of the segment
and the page number on which the segment description begins.
First look up the syntax for the statement, and then turn to the segment
description to find out the complete syntax for the segment. You will
probably never need to look up the segment first and then work backward to
a statement or statements that contain the segment.
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Informix Guide to SQL: Syntax
Segments
For example, if you are using INFORMIX-OnLine Dynamic Server, and you
want to enter a CREATE VIEW statement that includes a database name and
database server name in the view name, first look up the syntax diagram for
the CREATE VIEW statement. Then use the reference box for the View Name
segment in that syntax diagram to look up the subdiagram for the View
Name segment.
The subdiagram for the View Name segment shows you how to qualify the
simple name of a view with the name of the database or with the name of
both the database and the database server. Use the syntax in the subdiagram
to enter a CREATE VIEW statement that includes the database name and
database server name in the view name. The following example creates the
name_only view in the sales database on the boston database server:
CREATE VIEW sales@boston:name_only AS
SELECT customer_num, fname, lname FROM customer
Segments in This Section
This section describes the following segments:
■
Condition
■
Constraint Name
■
Database Name
■
Data Type
■
DATETIME Field Qualifier
■
Expression
■
Identifier
■
Index Name
■
INTERVAL Field Qualifier
■
Literal DATETIME
■
Literal INTERVAL
■
Literal Number
SQL Statements 1-641
Segments
1-642
■
Procedure Name
■
Quoted String
■
Relational Operator
■
Synonym Name
■
Table Name
■
View Name
Informix Guide to SQL: Syntax
Condition
Condition
A condition tests data to determine whether it meets certain qualifications.
Use the Condition segment wherever you see a reference to a condition in a
syntax diagram.
Syntax
AND
OR
NOT
Comparison
Condition
p. 1-644
Condition with
Subquery
p. 1-652
Usage
A condition is a collection of one or more search conditions, optionally
connected by the logical operators AND or OR. Search conditions fall into the
following categories:
■
Comparison conditions (also called filters or Boolean expressions)
■
Conditions with a subquery
Restrictions on a Condition
A condition can contain only an aggregate function if it is used in the HAVING
clause of a SELECT statement or the HAVING clause of a subquery. You cannot
use an aggregate function in a comparison condition that is part of a WHERE
clause in a DELETE, SELECT, or UPDATE statement unless the aggregate is on
a correlated column that originates from a parent query and the WHERE
clause is within a subquery that is within a HAVING clause.
SQL Statements 1-643
Condition
NOT Operator Option
If you preface a condition with the keyword NOT, the test is true only if the
condition that NOT qualifies is false. If the condition that NOT qualifies is
unknown (uses a null in the determination), the NOT operator has no effect.
The following truth table shows the effect of NOT. The letter T represents a
true condition, F represents a false condition, and a question mark (?)
represents an unknown condition. Unknown values occur when part of an
expression that uses an arithmetic operator is null.
NOT
T
F
F
T
?
?
Comparison Conditions (Boolean Expressions)
Five kinds of comparison conditions exist: Relational Operator, BETWEEN,
IN, IS NULL, and LIKE and MATCHES. Comparison conditions are often called
Boolean expressions because they evaluate to a simple true or false result.
Their syntax is summarized in the following diagram and explained in detail
after the diagram.
1-644
Informix Guide to SQL: Syntax
Condition
Comparison
Condition
Expression
p. 1-671
Relational
Operator
p. 1-761
Expression
p. 1-671
Expression
p. 1-671
Expression
p. 1-671
BETWEEN
NOT
,
Expression
p. 1-671
+
Expression
p. 1-671
AND
Literal
Number
p. 1-752
(
IN
NOT
)
Literal
DATETIME
p. 1-746
Literal
INTERVAL
p. 1-749
Quoted
String
p. 1-757
TODAY
Table
Name
p. 1-768
.
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
alias
.
USER
CURRENT
DATETIME
Field
Qualifier
p. 1-669
OL
SITENAME
DBSERVERNAME
column
name
IS
NULL
NOT
column
name
Table
Name
p. 1-768
.
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
alias
.
LIKE
NOT
+
MATCHES
Quoted
String
p. 1-757
ESCAPE 'char'
column name
SQL Statements 1-645
Condition
Element
alias
char
column name
Purpose
A temporary alternative name
for a table or view within the
scope of a SELECT statement
A single ASCII character that is to
be used as the escape character
within the quoted string in a
LIKE or MATCHES condition
The name of a column that is
used in an IS NULL condition or
in a LIKE or MATCHES condition.
See “IS NULL Condition” on
page 1-649 and “LIKE and
MATCHES Condition” on
page 1-649 for more information
on the meaning of column name
in these conditions.
Restrictions
You must have defined the alias
in the FROM clause of the SELECT
statement.
See “ESCAPE with LIKE” on
page 1-651 and “ESCAPE with
MATCHES” on page 1-652.
Syntax
Identifier, p. 1-723
The column must exist in the
specified table.
Identifier, p. 1-723
Quoted String,
p. 1-757
Refer to the following sections for more information on the use of the
different types of comparison conditions:
1-646
■
For relational-operator conditions, refer to “Relational-Operator
Condition” on page 1-647.
■
For the BETWEEN condition, refer to “BETWEEN Condition” on
page 1-648.
■
For the IN condition, refer to “IN Condition” on page 1-648.
■
For the IS NULL condition, refer to “IS NULL Condition” on
page 1-649.
■
For the LIKE and MATCHES condition, refer to “LIKE and MATCHES
Condition” on page 1-649.
Informix Guide to SQL: Syntax
Condition
Quotation Marks in Conditions
When you compare a column expression with a constant expression in any
type of comparison condition, observe the following rules:
■
If the column has a numeric data type, you do not need to surround
the constant expression with quotation marks.
■
If the column has a character data type, you must surround the constant expression with quotation marks.
■
If the column has a date data type, you should surround the constant
expression with quotation marks. Otherwise, you might get
unexpected results.
The following example shows the correct use of quotation marks in
comparison conditions. The ship_instruct column has a character data type.
The order_date column has a date data type. The ship_weight column has a
numeric data type.
SELECT * FROM orders
WHERE ship_instruct = 'express'
AND order_date > '05/01/94'
AND ship_weight < 30
Relational-Operator Condition
Some relational-operator conditions are shown in the following examples:
city[1,3] = 'San'
o.order_date > '6/12/86'
WEEKDAY(paid_date) = WEEKDAY(CURRENT-31 UNITS day)
YEAR(ship_date) < YEAR (TODAY)
quantity <= 3
customer_num <> 105
customer_num != 105
SQL Statements 1-647
Condition
If either expression is null for a row, the condition evaluates to false. For
example, if paid_date has a null value, you cannot use either of the following
statements to retrieve that row:
SELECT customer_num, order_date FROM orders
WHERE paid_date = ''
SELECT customer_num, order_date FROM orders
WHERE NOT PAID !=''
An IS NULL condition finds a null value, as shown in the following example.
The IS NULL condition is explained fully in “IS NULL Condition” on
page 1-649.
SELECT customer_num, order_date FROM orders
WHERE paid_date IS NULL
BETWEEN Condition
For a BETWEEN test to be true, the value of the expression on the left of the
BETWEEN keyword must be in the inclusive range of the values of the two
expressions on the right of the BETWEEN keyword. Null values do not satisfy
the condition. You cannot use NULL for either expression that defines the
range.
Some BETWEEN conditions are shown in the following examples:
order_date BETWEEN '6/1/93' and '9/7/93'
zipcode NOT BETWEEN '94100' and '94199'
EXTEND(call_dtime, DAY TO DAY) BETWEEN
(CURRENT - INTERVAL(7) DAY TO DAY) AND CURRENT
lead_time BETWEEN INTERVAL (1) DAY TO DAY
AND INTERVAL (4) DAY TO DAY
unit_price BETWEEN loprice AND hiprice
IN Condition
The IN condition is satisfied when the expression to the left of the word IN is
included in the list of items. The NOT option produces a search condition that
is satisfied when the expression is not in the list of items. Null values do not
satisfy the condition.
1-648
Informix Guide to SQL: Syntax
Condition
The following examples show some IN conditions:
WHERE state IN ('CA', 'WA', 'OR')
WHERE manu_code IN ('HRO', 'HSK')
WHERE user_id NOT IN (USER)
WHERE order_date NOT IN (TODAY)
ESQL
The TODAY function is evaluated at execution time; CURRENT is evaluated
when a cursor opens or when the query executes, if it is a singleton SELECT
statement. ♦
The USER function is case sensitive; it perceives minnie and Minnie as
different values.
IS NULL Condition
The IS NULL condition is satisfied if the column contains a null value. If you
use the IS NOT NULL option, the condition is satisfied when the column
contains a value that is not null. The following example shows an IS NULL
condition:
WHERE paid_date IS NULL
LIKE and MATCHES Condition
A LIKE or MATCHES condition tests for matching character strings. The
condition is true, or satisfied, when either of the following tests is true:
■
The value of the column on the left matches the pattern that the
quoted string specifies. You can use wildcard characters in the string.
Null values do not satisfy the condition.
■
The value of the column on the left matches the pattern that the
column on the right specifies. The value of the column on the right
serves as the matching pattern in the condition.
You can use the single quote (') only with the quoted string to match a literal
quote; you cannot use the ESCAPE keyword. You can use the quote character
as the escape character in matching any other pattern if you write it as ''''.
SQL Statements 1-649
Condition
NOT Option
The NOT option makes the search condition successful when the column on
the left has a value that is not null and does not match the pattern that the
quoted string specifies. For example, the following conditions exclude all
rows that begin with the characters Baxter in the lname column:
WHERE lname NOT LIKE 'Baxter%'
WHERE lname NOT MATCHES 'Baxter*'
LIKE Option
If you use the keyword LIKE, you can use the following wildcard characters
in the quoted string.
Wildcard
Meaning
%
The percent sign (%) matches zero or more characters.
_
The underscore (_) matches any single character.
\
The backslash (\) removes the special significance of the next
character (used to match % or _ by writing \% or \_).
Using the backslash (\) as an escape character is an Informix extension to
ANSI-compliant SQL.
ANSI
If you use an escape character to escape anything other than percent sign (%),
underscore (_), or the escape character itself, an error is returned. ♦
The following condition tests for the string tennis, alone or in a longer
string, such as tennis ball or table tennis paddle:
WHERE description LIKE '%tennis%'
The following condition tests for all descriptions that contain an underscore.
The backslash (\) is necessary because the underscore (_) is a wildcard
character.
WHERE description LIKE '%\_%'
1-650
Informix Guide to SQL: Syntax
Condition
MATCHES Option
If you use the keyword MATCHES, you can use the following wildcard
characters in the quoted string.
Wildcard
Meaning
*
The asterisk (*) matches zero or more characters.
?
The question mark (?) matches any single character.
[...]
The brackets ([...]) match any of the enclosed characters,
including character ranges as in [a to z]. A caret (^) as the
first character within the brackets matches any character that
is not listed. Hence [^abc] matches any character that is not
a, b, or c.
\
The backslash (\) removes the special significance of the next
character (used to match * or ? by writing \* or \?).
The following condition tests for the string tennis, alone or in a longer
string, such as tennis ball or table tennis paddle:
WHERE description MATCHES '*tennis*'
The following condition is true for the names Frank and frank:
WHERE fname MATCHES '[Ff]rank'
The following condition is true for any name that begins with either F or f:
WHERE fname MATCHES '[Ff]*'
ESCAPE with LIKE
The ESCAPE clause lets you include an underscore (_) or a percent sign (%) in
the quoted string and avoid having them be interpreted as wildcards. If you
choose to use z as the escape character, the characters z_ in a string stand for
the character _. Similarly, the characters z% represent the percent sign (%).
Finally, the characters zz in the string stand for the single character z. The
following statement retrieves rows from the customer table in which the
company column includes the underscore character:
SELECT * FROM customer
WHERE company LIKE '%z_%' ESCAPE 'z'
SQL Statements 1-651
Condition
You can also use a single-character host variable as an escape character. The
following statement shows the use of a host variable as an escape character:
EXEC SQL BEGIN DECLARE SECTION;
char escp='z';
char fname[20];
EXEC SQL END DECLARE SECTION;
EXEC SQL select fname from customer
into :fname
where company like '%z_%' escape :escp;
ESCAPE with MATCHES
The ESCAPE clause lets you include a question mark (?), an asterisk (*), and a
left or right bracket ([]) in the quoted string and avoid having them be interpreted as wildcards. If you choose to use z as the escape character, the
characters z? in a string stand for the question mark (?). Similarly, the
characters z* stand for the asterisk (*). Finally, the characters zz in the string
stand for the single character z.
The following example retrieves rows from the customer table in which the
value of the company column includes the question mark (?):
SELECT * FROM customer
WHERE company MATCHES '*z?*' ESCAPE 'z'
Condition with a Subquery
Condition
with
Subquery
IN
Subquery
p. 1-653
EXISTS
Subquery
p. 1-654
ALL/ANY/SOME
Subquery
p. 1-655
1-652
Informix Guide to SQL: Syntax
Condition
You can use a SELECT statement within a condition; this combination is called
a subquery. You can use a subquery in a SELECT statement to perform the
following functions:
■
Compare an expression to the result of another SELECT statement
■
Determine whether an expression is included in the results of
another SELECT statement
■
Ask whether another SELECT statement selects any rows
The subquery can depend on the current row that the outer SELECT statement
is evaluating; in this case, the subquery is a correlated subquery.
The kinds of subquery conditions are shown in the following sections with
their syntax.
A subquery can return a single value, no value, or a set of values depending
on the context in which it is used. If a subquery returns a value, it must select
only a single column. If the subquery simply checks whether a row (or rows)
exists, it can select any number of rows and columns. A subquery cannot
contain an ORDER BY clause. The full syntax of the SELECT statement is
described on page 1-459.
IN Subquery
IN
Subquery
Expression
p. 1-671
IN
NOT
(
Condition
with
Subquery
p. 1-652
)
An IN subquery condition is true if the value of the expression matches one
or more of the values that the subquery selects. The subquery must return
only one column, but it can return more than one row. The keyword IN is
equivalent to the =ANY sequence. The keywords NOT IN are equivalent to the
!=ALL sequence. See “ALL/ANY/SOME Subquery” on page 1-655.
SQL Statements 1-653
Condition
The following example of an IN subquery finds the order numbers for orders
that do not include baseball gloves (stock_num = 1):
WHERE order_num NOT IN
(SELECT order_num FROM items WHERE stock_num = 1)
Because the IN subquery tests for the presence of rows, duplicate rows in the
subquery results do not affect the results of the main query. Therefore, you
can put the UNIQUE or DISTINCT keyword into the subquery with no effect
on the query results, although eliminating testing duplicates can reduce the
time needed for running the query.
EXISTS Subquery
EXISTS
Subquery
EXISTS
NOT
(
Condition
with
Subquery
p. 1-652
)
An EXISTS subquery condition evaluates to true if the subquery returns a row.
With an EXISTS subquery, one or more columns can be returned. The
subquery always contains a reference to a column of the table in the main
query. If you use an aggregate function in an EXISTS subquery, at least one
row is always returned.
The following example of a SELECT statement with an EXISTS subquery
returns the stock number and manufacturer code for every item that has
never been ordered (and is therefore not listed in the items table). You can
appropriately use an EXISTS subquery in this SELECT statement because you
use the subquery to test both stock_num and manu_code in items.
SELECT stock_num, manu_code FROM stock
WHERE NOT EXISTS (SELECT stock_num, manu_code FROM items
WHERE stock.stock_num = items.stock_num AND
stock.manu_code = items.manu_code)
The preceding example works equally well if you use SELECT * in the
subquery in place of the column names because the existence of the whole
row is tested; specific column values are not tested.
1-654
Informix Guide to SQL: Syntax
Condition
ALL/ANY/SOME Subquery
ANY/ALL/SOME
Subquery
Expression
p. 1-671
Relational
Operator
p. 1-761
(
ALL
ANY
SOME
Condition
with
Subquery
p. 1-652
)
You use the ALL, ANY, and SOME keywords to specify what makes the search
condition true or false. A search condition that is true when the ANY keyword
is used might not be true when the ALL keyword is used, and vice versa.
Keyword
Meaning
ALL
A keyword that denotes that the search condition is true if the
comparison is true for every value that the subquery returns.
If the subquery returns no value, the condition is true.
ANY
A keyword that denotes that the search condition is true if the
comparison is true for at least one of the values that is
returned. If the subquery returns no value, the search
condition is false.
SOME
An alias for ANY
In the following example of the ALL subquery, the first condition tests
whether each total_price is greater than the total price of every item in order
number 1023. The second condition uses the MAX aggregate function to
produce the same results.
total_price > ALL (SELECT total_price FROM items
WHERE order_num = 1023)
total_price > (SELECT MAX(total_price) FROM items
WHERE order_num = 1023)
SQL Statements 1-655
Condition
The following conditions are true when the total price is greater than the total
price of at least one of the items in order number 1023. The first condition
uses the ANY keyword; the second uses the MIN aggregate function.
total_price > ANY (SELECT total_price FROM items
WHERE order_num = 1023)
total_price > (SELECT MIN(total_price) FROM items
WHERE order_num = 1023)
Using the NOT keyword with an ANY subquery tests whether an expression
is not true for any subquery value. The condition, which is found in the
following example of the NOT keyword with an ANY subquery, is true when
the expression total_price is not greater than any selected value. That is, it is
true when total_price is greater than none of the total prices in order number
1023.
NOT total_price > ANY (SELECT total_price FROM items
WHERE order_num = 1023)
Omitting ANY, ALL, or SOME Keywords
You can omit the keywords ANY, ALL, or SOME in a subquery if you know
that the subquery will return exactly one value. If you omit the ANY, ALL, or
SOME keywords, and the subquery returns more than one value, you receive
an error. The subquery in the following example returns only one row
because it uses an aggregate function:
SELECT order_num FROM items
WHERE stock_num = 9 AND quantity =
(SELECT MAX(quantity) FROM items WHERE stock_num = 9)
Conditions with AND or OR
You can combine simple conditions with the logical operators AND or OR to
form complex conditions. The following SELECT statements contain
examples of complex conditions in their WHERE clauses:
SELECT customer_num, order_date FROM orders
WHERE paid_date > '1/1/93' OR paid_date IS NULL
SELECT order_num, total_price FROM items
WHERE total_price > 200.00 AND manu_code LIKE 'H%'
SELECT lname, customer_num FROM customer
WHERE zipcode BETWEEN '93500' AND '95700'
OR state NOT IN ('CA', 'WA', 'OR')
1-656
Informix Guide to SQL: Syntax
Condition
The following truth tables show the effect of the AND and OR operators.The
letter T represents a true condition, F represents a false condition, and the
question mark (?) represents an unknown value. Unknown values occur
when part of an expression that uses a logical operator is null.
AND
T
F
?
OR
T
F
?
T
T
F
?
T
T
T
T
F
F
F
F
F
T
F
?
?
?
F
?
?
T
?
?
If the Boolean expression evaluates to UNKNOWN, the condition is not satisfied.
Consider the following example within a WHERE clause:
WHERE ship_charge/ship_weight < 5
AND order_num = 1023
The row where order_num = 1023 is the row where ship_weight is null.
Because ship_weight is null, ship_charge/ship_weight is also null;
therefore, the truth value of ship_charge/ship_weight < 5 is UNKNOWN.
Because order_num = 1023 is TRUE, the AND table states that the truth value
of the entire condition is UNKNOWN. Consequently, that row is not chosen. If the
condition used an OR in place of the AND, the condition would be true.
References
In the Informix Guide to SQL: Tutorial, see the discussion of conditions in the
SELECT statement in Chapter 2 and Chapter 3.
In the Guide to GLS Functionality, see the discussion of the SELECT statement
for information on the GLS aspects of conditions.
SQL Statements 1-657
Constraint Name
Constraint Name
The Constraint Name segment specifies the name of a constraint. Use the
Constraint Name segment whenever you see a reference to a constraint name
in a syntax diagram.
Syntax
Identifier
p. 1-723
owner.
OL
:
database
'owner'.
@dbservername
Element
database
dbservername
owner
1-658
Purpose
The name of the database where
the constraint resides
The name of the OnLine
database server that is home to
database. The @ symbol is a literal
character that introduces the
database server name.
The user name of the owner of
the constraint
Informix Guide to SQL: Syntax
Restrictions
The database must exist.
The database server that
dbservername specifies must
match the name of a database
server in the sqlhosts file.
If you are using an ANSIcompliant database, you must
enter the owner. parameter for a
constraint that you do not own.
If you put quotation marks
around the name that you enter
in owner, the name is stored
exactly as typed. If you do not
put quotation marks around the
name that you enter in owner, the
name is stored as uppercase
letters.
Syntax
Database Name,
p. 1-660
Database Name,
p. 1-660
The user name must
conform to the
conventions of your
operating system.
Constraint Name
Usage
The actual name of the constraint is an <vk>SQL identifier.
GLS
If you are using a nondefault locale, you can use characters from the code set
of your locale in the names of constraints. For more information, see
Chapter 3 of the Guide to GLS Functionality. ♦
When you create a constraint, the name of the constraint must be unique
within the database if the database is not ANSI compliant.
ANSI
When you create a constraint, the owner.name combination (the combination
of the owner name and constraint name) must be unique within a database.
The owner.name combination is case sensitive. In an ANSI-compliant database,
if you do not use quotes around the owner name, the name of the constraint
owner is stored as uppercase letters. For more information, see the discussion
of case sensitivity in ANSI-compliant databases on page 1-770. ♦
References
See the CREATE TABLE statement in this manual for information on defining
constraints.
SQL Statements 1-659
Database Name
Database Name
The Database Name segment specifies the name of a database. Use the
Database Name segment whenever you see a reference to a database name in
a syntax diagram.
Syntax
dbname
OL
OL
@ dbservername
' //dbservername/dbname '
ESQL
variable name
SE
' //dbservername/pathname/dbname '
' /pathname/dbname@dbservername '
1-660
Informix Guide to SQL: Syntax
Database Name
Element
dbname
dbservername
pathname
Purpose
The name of the database itself.
This simple name does not
include the pathname or the
database server name.
Restrictions
A database name must be
unique among the database
names on the same database
server. Database names are not
case sensitive. If you are using
OnLine, the database name can
have a maximum of 18
characters. If you are using
INFORMIX-SE, the database
name can have a maximum of 10
characters. For restrictions on
dbname that are specific to syntax
formats that use quotation
marks and slash symbols, see
“//dbservername/dbname
Option” on page 1-663 and
“Specifying Server Names for
INFORMIX-SE Databases” on
page 1-663.
The name of the database server The database server that is
on which the database that is
specified in dbservername must
named in dbname resides. The @ match the name of a database
symbol is a literal character that server in the sqlhosts file. You
introduces the database server
can put a space between dbname
name. Specifying a database
and the @ symbol, or you can
server name allows you to
omit the space. You cannot put a
choose a database on another
space between the @ symbol and
database server as your current dbservername. For restrictions on
database. You can name the
dbservername that are specific to
current database server using
syntax formats that use
dbservername, although that is
quotation marks and slash
extra information.
symbols, see “//dbservername/dbname Option” on
page 1-663 and “Specifying
Server Names for INFORMIXSE Databases” on page 1-663.
The pathname of the database
The specified path must exist.
directory up to the parent
For punctuation restrictions on
directory of the .dbs directory
pathname, see “Specifying Server
Names for INFORMIX-SE
Databases” on page 1-663.
Syntax
Identifier, p. 1-723
Identifier, p. 1-723
The pathname must
conform to the
conventions of your
operating system.
(1 of 2)
SQL Statements 1-661
Database Name
Element
variable name
Purpose
Restrictions
The name of a host variable that See “variable name Option” on
holds the name of a database
page 1-663 for restrictions that
apply when you are using
INFORMIX-SE and you want to
specify a database that does not
reside either in your current
directory or in a directory that
the DBPATH environment
variable specifies.
Syntax
The name of the host
variable must
conform to
language-specific
rules for variable
names.
(2 of 2)
Usage
The simple database name is an <vk>SQL identifier, as described on
page 1-723. If you are creating a database, the name that you assign to the
database can be 18 characters, inclusive. Database names are not case
sensitive. You cannot use delimited identifiers for a database name.
SE
Database names in INFORMIX-SE databases can be 10 characters, inclusive. ♦
The maximum length of the database name and directory path, including
dbservername, is 128 characters.
The following example shows a database specification:
empinfo@personnel
GLS
If you are using a nondefault locale, you can use characters from the code set
of your locale in the names of databases. For more information, see Chapter 3
of the Guide to GLS Functionality. ♦
@dbservername Option
If you use a database server name, do not put any spaces between the name
and the @ symbol. For example, the following format is valid for the stores7
database on the training database server:
stores7@training
1-662
Informix Guide to SQL: Syntax
Database Name
//dbservername/dbname Option
If you use the alternative naming method, do not put spaces between the
quotes, slashes, and names, as the following example shows:
'//training/stores7'
variable name Option
ESQL
SE
ESQL
You can use a variable within an SQL API to hold the name of a database. ♦
If you want to specify a database that resides neither in your current
directory nor in a directory that the DBPATH environment variable specifies,
you must specify a program variable that evaluates to the full pathname of
the database (excluding the .dbs extension). ♦
Specifying Server Names for INFORMIX-SE Databases
SE
You can specify a database on a specific database server. Do not put spaces
between the quotes, slashes, and names. The following database name
describes a stores7 database that resides on the business database server:
//business/u/acctng/demo/stores7
♦
SE
GLS
If you are using a nondefault locale that contains a multibyte code set, you
must make sure that an SE database name meets the 10-byte size restriction.
For more information, see the discussion on naming databases in Chapter 5
of the Guide to GLS Functionality. ♦
References
See the CREATE DATABASE and RENAME DATABASE statements in this
manual for information on naming databases.
SQL Statements 1-663
Data Type
Data Type
The Data Type segment specifies the data type of a column or value. Use the
Data Type segment whenever you see a reference to a data type in a syntax
diagram.
1-664
Informix Guide to SQL: Syntax
Data Type
Syntax
CHAR
(
CHARACTER
)
size
(1)
GLS
NCHAR
+
+
DATE
+
DATETIME
DATETIME Field Qualifier p. 1-669
DECIMAL
(
DEC
)
precision
NUMERIC
, scale
16
FLOAT
(
float
precision
)
DOUBLE PRECISION
INTEGER
INT
+
INTERVAL
+
MONEY
INTERVAL Field Qualifier p. 1-743
(
)
precision
16
,2
, scale
SERIAL
+
(
+
(1)
start
)
SMALLFLOAT
REAL
SMALLINT
OL
INFORMIX-OnLine Dynamic Server-Specific Data Types p. 1-666
SQL Statements 1-665
Data Type
INFORMIX-OnLine Dynamic Server-Specific Data Types
INFORMIX-OnLine Dynamic
Server-Specific
Data Types
+
TEXT
+
BYTE
IN
TABLE
blobspace
OP
family name
+
VARCHAR
(
)
max
,
reserve
GLS
+
,0
NVARCHAR
CHARACTER VARYING
(
)
max
reserve
Element
blobspace
family name
,
Purpose
Name of an existing blobspace
Quoted string constant that
specifies a family name or
variable name in the optical
family
Restrictions
The blobspace must exist.
The family name or variable
name must exist.
float precision
The float precision is ignored.
max
Maximum size of a
You must specify a positive Literal Number, p. 1-752
integer.
You must specify an integer Literal Number, p. 1-752
value between 1 and 255
bytes inclusive. If you place
an index on the column, the
largest value you can
specify for max is 254 bytes.
CHARACTER VARYING or
VARCHAR or NVARCHAR
column in bytes
Syntax
Identifier, p. 1-723
Quoted String, p. 1-757
For additional information
about optical families, see
INFORMIX-OnLine/Opti
cal User Manual.
(1 of 2)
1-666
Informix Guide to SQL: Syntax
Data Type
Element
precision
reserve
scale
size
Purpose
Total number of significant
digits in a decimal or money
data type
Amount of space in bytes
reserved for a CHARACTER
VARYING or VARCHAR or
NVARCHAR column even if the
actual number of bytes stored
in the column is less than
reserve
Number of digits to the right of
the decimal point
Number of bytes in the CHAR
or NCHAR column.
Restrictions
Syntax
You must specify an integer Literal Number, p. 1-752
between 1 and 32, inclusive.
You must specify an integer Literal Number, p. 1-752
value between 0 and 255
bytes. However, the value
you specify for reserve must
be less than the value you
specify for max.
You must specify an integer Literal Number, p. 1-752
between 1 and precision.
For OnLine, you must
Literal Number, p. 1-752
specify an integer value
between 1 and 32,767 bytes
inclusive.
For SE, you must specify an
integer value between 1 and
32,511 bytes inclusive.
Starting number for values in a You must specify an integer Literal Number, p. 1-752
SERIAL column
greater than 0 and less than
2,147,483,647.
start
(2 of 2)
For more information, see the discussion of all data types in Chapter 3 of the
Informix Guide to SQL: Reference.
Fixed and Varying Length Data Types
The data type CHAR is for fixed-length character data. Use the ANSIcompliant CHARACTER VARYING data type to specify varying length
character data. You can also specify varying length data with the Informix
VARCHAR data type.
NCHAR and NVARCHAR Data Types
GLS
See Chapter 3 of the Guide to GLS Functionality for a discussion of the NCHAR
and NVARCHAR data types. ♦
SQL Statements 1-667
Data Type
References
In the Informix Guide to SQL: Reference, see the discussions of individual data
types in Chapter 3.
In the Informix Guide to SQL: Tutorial, see the discussion of data types in
Chapter 9.
In the Guide to GLS Functionality, see the discussion of the NCHAR and
NVARCHAR data types and the GLS aspects of other character data types.
1-668
Informix Guide to SQL: Syntax
DATETIME Field Qualifier
DATETIME Field Qualifier
A DATETIME field qualifier specifies the largest and smallest unit of time in a
DATETIME column or value. Use the DATETIME Field Qualifier segment
whenever you see a reference to a DATETIME field qualifier in a syntax
diagram.
Syntax
YEAR
MONTH
TO YEAR
DAY
TO MONTH
HOUR
MINUTE
TO DAY
TO HOUR
SECOND
TO MINUTE
FRACTION
TO SECOND
TO FRACTION
(3)
(digit)
Element
digit
Purpose
Restrictions
A single integer that specifies the You must specify an integer
precision of a decimal fraction of between 1 and 5, inclusive.
a second. The default precision is
3 digits (a thousandth of a
second).
Syntax
Literal Number,
p. 1-752
SQL Statements 1-669
DATETIME Field Qualifier
Usage
Specify the largest unit for the first DATETIME value; after the word TO,
specify the smallest unit for the value. The keywords imply that the
following values are used in the DATETIME object.
Unit of Time
Meaning
YEAR
Specifies a year, numbered from A.D. 1 to 9999
MONTH
Specifies a month, numbered from 1 to 12
DAY
Specifies a day, numbered from 1 to 31, as appropriate to the
month in question
HOUR
Specifies an hour, numbered from 0 (midnight) to 23
MINUTE
Specifies a minute, numbered from 0 to 59
SECOND
Specifies a second, numbered from 0 to 59
FRACTION
Specifies a fraction of a second, with up to five decimal places.
The default scale is three digits (thousandth of a second).
The following examples show DATETIME qualifiers:
DAY TO MINUTE
YEAR TO MINUTE
DAY TO FRACTION(4)
MONTH TO MONTH
References
In the Informix Guide to SQL: Reference, see the DATETIME data type in
Chapter 3 for an explanation of the DATETIME field qualifier.
1-670
Informix Guide to SQL: Syntax
Expression
Expression
An expression is one or more pieces of data that is contained in or derived
from the database or database server. Use the Expression segment whenever
you see a reference to an expression in a syntax diagram.
Syntax
+
*
/
||
Column
Expressions
p. 1-673
+
Constant
Expressions
p. 1-676
Function
Expressions
p. 1-683
Aggregate
Expressions
p. 1-709
Procedure Call
Expressions
p. 1-722
variable name
SPL
procedure variable name
(
Expression
)
SQL Statements 1-671
Expression
Element
procedure
variable name
variable name
Purpose
The name of a variable that is
defined in a stored procedure.
The value stored in the variable
is one of the expression types
that is shown in the syntax
diagram.
The name of a program variable
or host variable. The value
stored in the variable is one of
the expression types shown in
the syntax diagram.
Restrictions
The expression that is stored in
procedure variable name must
conform to the rules for expressions of that type.
Syntax
Identifier, p. 1-723
The expression that is stored in
variable name must conform to
the rules for expressions of that
type.
The name of the
variable must
conform to
language-specific
rules for variable
names.
Usage
To combine expressions, connect them with arithmetic operators for
addition, subtraction, multiplication, and division.
You cannot use an aggregate expression in a condition that is part of a WHERE
clause unless the aggregate expression is used within a subquery.
Concatenation Operator
You can use the concatenation operator (||) to concatenate two expressions.
For example, the following examples are some possible concatenatedexpression combinations. The first example concatenates the zipcode column
to the first three letters of the lname column. The second example
concatenates the suffix .dbg to the contents of a host variable called
file_variable. The third example concatenates the value returned by the
TODAY function to the string Date.
lname[1,3] || zipcode
:file_variable || '.dbg'
'Date:' || TODAY
1-672
Informix Guide to SQL: Syntax
Expression
ESQL
You cannot use the concatenation operator in an embedded-language-only
statement. The SQL API-only statements appear in the following list.
ALLOCATE DESCRIPTOR
CLOSE
CONNECT TO
DEALLOCATE DESCRIPTOR
DECLARE
DESCRIBE
DISCONNECT
FETCH
FLUSH
FREE
GET DESCRIPTOR
OPEN
PREPARE
PUT
EXECUTE
EXECUTE IMMEDIATE
SET CONNECTION
SET DESCRIPTOR
♦
Column Expressions
The possible syntax for column expressions is shown in the following
diagram.
column
name
Table
Name
p. 1-768
.
alias
.
+
+
View
Name
p. 1-772
.
Synonym
Name
p. 1-766
.
[first, last ]
ROWID
SQL Statements 1-673
Expression
Element
alias
column name
Purpose
A temporary alternative name
for a table or view within the
scope of a SELECT statement.
This alternative name is established in the FROM clause of the
SELECT statement.
The name of the column that you
are specifying
first
The position of the first character
in the portion of the column that
you are selecting
last
The position of the last character
in the portion of the column that
you are selecting
Restrictions
The restrictions depend on the
clause of the SELECT statement
in which alias occurs.
Syntax
Identifier, p. 1-723
The restrictions depend on the
statement in which column name
occurs.
The column must be one of the
following types: BYTE, CHAR,
NCHAR, NVARCHAR, TEXT, or
VARCHAR.
The column must be one of the
following types: BYTE, CHAR,
NCHAR, NVARCHAR, TEXT, or
VARCHAR.
Identifier, p. 1-723
Literal Number,
p. 1-752
Literal Number,
p. 1-752
The following examples show column expressions:
company
items.price
cat_advert [1,15]
Use a table or alias name whenever it is necessary to distinguish between
columns that have the same name but are in different tables. The SELECT
statements that the following example shows use customer_num from the
customer and orders tables. The first example precedes the column names
with table names. The second example precedes the column names with table
aliases.
SELECT * FROM customer, orders
WHERE customer.customer_num = orders.customer_num
SELECT * FROM customer c, orders o
WHERE c.customer_num = o.customer_num
1-674
Informix Guide to SQL: Syntax
Expression
Using Subscripts on Character Columns
You can use subscripts on CHAR, VARCHAR, NCHAR, NVARCHAR, BYTE,
and TEXT columns. The subscripts indicate the starting and ending character
positions that are contained in the expression. Together the column
subscripts define a column substring. The column substring is the portion of
the column that is contained in the expression.
For example, if a value in the lname column of the customer table is
Greenburg, the following expression evaluates to burg:
lname[6,9]
GLS
For information on the GLS aspects of column subscripts and substrings, see
the Guide to GLS Functionality, Chapter 3. ♦
Using Rowids
You can use the rowid column that is associated with a table row as a
property of the row. The rowid column is essentially a hidden column in
nonfragmented tables and in fragmented tables that were created with the
WITH ROWIDS clause. The rowid column is unique for each row, but it is not
necessarily sequential. Informix recommends, however, that you utilize
primary keys as an access method rather than exploiting the rowid column.
SE
The rowid column is sequential and starts at 1 for each table. ♦
The following examples show possible uses of the ROWID keyword in a
SELECT statement:
SELECT *, ROWID FROM customer
SELECT fname, ROWID FROM customer
ORDER BY ROWID
SELECT HEX(rowid) FROM customer
WHERE customer_num = 106
In INFORMIX-OnLine Dynamic Server only, the last SELECT statement
example shows how to get the page number (the first six digits after 0x) and
the slot number (the last two digits) of the location of your row.
You cannot use ROWID keyword in the select list of a query that contains an
aggregate function.
SQL Statements 1-675
Expression
Constant Expressions
The following diagram shows the possible syntax for constant expressions.
Quoted
String
p. 1-757
USER
OL
+
SITENAME
DBSERVERNAME
+
Literal
Number
p. 1-752
TODAY
CURRENT
DATETIME
Field Qualifier
p. 1-669
Literal
DATETIME
p. 1-746
Literal
INTERVAL
p. 1-749
n
1-676
Informix Guide to SQL: Syntax
UNITS
datetime
unit
Expression
■
For the CURRENT function in an expression, see “CURRENT
Function” on page 1-680.
■
For literal DATETIME as an expression, see “Literal DATETIME as an
Expression” on page 1-681.
■
For literal INTERVAL as an expression, see “Literal INTERVAL as an
Expression” on page 1-682.
■
For the UNITS keyword in an expression, see “UNITS Keyword” on
page 1-682.
Quoted String as an Expression
The following examples show quoted strings as expressions:
SELECT 'The first name is ', fname FROM customer
INSERT INTO manufact VALUES ('SPS', 'SuperSport')
UPDATE cust_calls SET res_dtime = '1993-1-1 10:45'
WHERE customer_num = 120 AND call_code = 'B'
USER Function
The USER function returns a string that contains the login name of the current
user (that is, the person running the process).
The following statements show how you might use the USER function:
INSERT INTO cust_calls VALUES
(221,CURRENT,USER,'B','Decimal point off', NULL, NULL)
SELECT * FROM cust_calls WHERE user_id = USER
UPDATE cust_calls SET user_id = USER WHERE customer_num = 220
The USER function does not change the case of a user ID. If you use USER in
an expression and the present user is Robertm, the USER function returns
Robertm, not robertm. If you specify user as the default value for a column,
the column must be CHAR, VARCHAR, NCHAR, or NVARCHAR data type, and
it must be at least eight characters long.
1-678
Informix Guide to SQL: Syntax
Expression
ANSI
In an ANSI-compliant database, if you do not use quotes around the owner
name, the name of the table owner is stored as uppercase letters. If you use
the USER keyword as part of a condition, you must be sure that the way the
user name is stored agrees with the values that the USER function returns,
with respect to case. ♦
SITENAME and DBSERVERNAME Functions
The SITENAME and DBSERVERNAME functions return the database server
name, as defined in the ONCONFIG file for the INFORMIX-OnLine Dynamic
Server installation where the current database resides or as specified in the
INFORMIXSERVER environment variable. The two function names,
SITENAME and DBSERVERNAME, are synonymous. You can use the
DBSERVERNAME function to determine the location of a table, to put information into a table, or to extract information from a table. You can insert
DBSERVERNAME into a simple character field or use it as a default value for
a column. If you specify DBSERVERNAME as a default value for a column, the
column must be CHAR, VARCHAR, NCHAR, or NVARCHAR data type and
must be at least 18 characters long.
In the following example, the first statement returns the name of the database
server where the customer table resides. Because the query is not restricted
with a WHERE clause, it returns DBSERVERNAME for every row in the table.
If you add the DISTINCT keyword to the SELECT clause, the query returns
DBSERVERNAME once. The second statement adds a row that contains the
current site name to a table. The third statement returns all the rows that have
the site name of the current system in site_col. The last statement changes the
company name in the customer table to the current system name.
SELECT DBSERVERNAME FROM customer
INSERT INTO host_tab VALUES ('1', DBSERVERNAME)
SELECT * FROM host_tab WHERE site_col = DBSERVERNAME
UPDATE customer SET company = DBSERVERNAME
WHERE customer_num = 120
SQL Statements 1-679
Expression
Literal Number as an Expression
The following examples show literal numbers as expressions:
INSERT INTO items VALUES (4, 35, 52, 'HRO', 12, 4.00)
INSERT INTO acreage VALUES (4, 5.2e4)
SELECT unit_price + 5 FROM stock
SELECT -1 * balance FROM accounts
TODAY Function
Use the TODAY function to return the system date as a DATE data type. If you
specify TODAY as a default value for a column, it must be a DATE column.
The following examples show how you might use the TODAY function in an
INSERT, UPDATE, or SELECT statement:
UPDATE orders (order_date) SET order_date = TODAY
WHERE order_num = 1005
INSERT INTO orders VALUES
(0, TODAY, 120, NULL, N, '1AUE217', NULL, NULL, NULL, NULL)
SELECT * FROM orders WHERE ship_date = TODAY
CURRENT Function
The CURRENT function returns a DATETIME value with the date and time of
day, showing the current instant.
If you do not specify a datetime qualifier, the default qualifiers are YEAR TO
FRACTION(3). You can use the CURRENT function in any context in which you
can use a literal DATETIME (see page 1-746). If you specify CURRENT as the
default value for a column, it must be a DATETIME column and the qualifier
of CURRENT must match the column qualifier, as the following example
shows:
CREATE TABLE new_acct (col1 int, col2 DATETIME YEAR TO DAY
DEFAULT CURRENT YEAR TO DAY)
If you use the CURRENT keyword in more than one place in a single
statement, identical values can be returned at each point of the call. You
cannot rely on the CURRENT function to provide distinct values each time it
executes.
1-680
Informix Guide to SQL: Syntax
Expression
The returned value comes from the system clock and is fixed when any SQL
statement starts. For example, any calls to CURRENT from an EXECUTE
PROCEDURE statement return the value when the stored procedure starts.
The CURRENT function is always evaluated in the database server where the
current database is located. If the current database is in a remote database
server, the returned value is from the remote host.
The CURRENT function might not execute in the physical order in which it
appears in a statement. You should not use the CURRENT function to mark
the start, end, or a specific point in the execution of a statement.
If your platform does not provide a system call that returns the current time
with subsecond precision, the CURRENT function returns a zero for the
FRACTION field.
In the following example, the first statement uses the CURRENT function in a
WHERE condition. The second statement uses the CURRENT function as the
input for the DAY function. The last query selects rows whose call_dtime
value is within a range from the beginning of 1993 to the current instant.
DELETE FROM cust_calls WHERE
res_dtime < CURRENT YEAR TO MINUTE
SELECT * FROM orders WHERE DAY(ord_date) < DAY(CURRENT)
SELECT * FROM cust_calls WHERE call_dtime
BETWEEN '1993-1-1 00:00:00' AND CURRENT
Literal DATETIME as an Expression
The following examples show literal DATETIME as an expression:
SELECT DATETIME (1993-12-6) YEAR TO DAY FROM customer
UPDATE cust_calls SET res_dtime = DATETIME (1992-07-07 10:40)
YEAR TO MINUTE
WHERE customer_num = 110
AND call_dtime = DATETIME (1992-07-07 10:24) YEAR TO MINUTE
SELECT * FROM cust_calls
WHERE call_dtime
= DATETIME (1995-12-25 00:00:00) YEAR TO SECOND
SQL Statements 1-681
Expression
Literal INTERVAL as an Expression
The following examples show literal INTERVAL as an expression:
INSERT INTO manufact VALUES ('CAT', 'Catwalk Sports',
INTERVAL (16) DAY TO DAY)
SELECT lead_time + INTERVAL (5) DAY TO DAY FROM manufact
The second statement in the preceding example adds five days to each value
of lead_time selected from the manufact table.
UNITS Keyword
The UNITS keyword enables you to display a simple interval or increase or
decrease a specific interval or datetime value.
If n is not an integer, it is rounded down to the nearest whole number when
it is used.
In the following example, the first SELECT statement uses the UNITS keyword
to select all the manufacturer lead times, increased by five days. The second
SELECT statement finds all the calls that were placed more than 30 days ago.
If the expression in the WHERE clause returns a value greater than 99
(maximum number of days), the query fails. The last statement increases the
lead time for the ANZA manufacturer by two days.
SELECT lead_time + 5 UNITS DAY FROM manufact
SELECT * FROM cust_calls
WHERE (TODAY - call_dtime) > 30 UNITS DAY
UPDATE manufact SET lead_time = 2 UNITS DAY + lead_time
WHERE manu_code = 'ANZ'
1-682
Informix Guide to SQL: Syntax
Expression
Function Expressions
A function expression takes an argument, as the following diagram shows.
+
Algebraic
Functions
p. 1-684
DBINFO
Function
p. 1-690
Exponential and
Logarithmic
Functions
p. 1-694
HEX Function
p. 1-696
Length
Functions
p. 1-696
Time Functions
p. 1-699
Trigonometric
Functions
p. 1-704
TRIM Function
p. 1-707
The following examples show function expressions:
EXTEND (call_dtime, YEAR TO SECOND)
MDY (12, 7, 1900 + cur_yr)
DATE (365/2)
LENGTH ('abc') + LENGTH (pvar)
HEX (customer_num)
HEX (LENGTH(123))
TAN (radians)
SQL Statements 1-683
Expression
ABS (-32)
EXP (4,3)
MOD (10,3)
Algebraic Functions
An algebraic function takes one or more arguments, as the following diagram
shows.
Algebraic
Functions
)
ABS
(
MOD
(
dividend, divisor
)
POW
(
base, exponent
)
ROOT
(
radicand
num_expression
)
, index
,2
ROUND
(
)
Expression
p. 1-671
, rounding factor
,0
SQRT
(
TRUNC
(
sqrt_radicand
)
)
Expression
p. 1-671
, truncating factor
,0
1-684
Informix Guide to SQL: Syntax
Expression
Element
base
dividend
divisor
exponent
index
Purpose
A value to be raised to the power
that is specified in exponent. The
base value is the first argument
that is supplied to the POW
function. See “POW Function”
on page 1-688 for further
information on base.
A value to be divided by the
value in divisor. The dividend
value is the first argument
supplied to the MOD function.
See “MOD Function” on
page 1-687 for further
information on dividend.
The value by which the value in
dividend is to be divided. The
divisor value is the second
argument that is supplied to the
MOD function. See “MOD
Function” on page 1-687 for
further information on divisor
The power to which the value
that is specified in base is to be
raised. The exponent value is the
second argument that is
supplied to the POW function.
See “POW Function” on
page 1-688 for further
information on exponent.
The type of root to be returned,
where 2 represents square root, 3
represents cube root, and so on.
The index value is the second
argument that is supplied to the
ROOT function. The default
value of index is 2. See “ROOT
Function” on page 1-688 for
further information on index.
Restrictions
You can enter in base any real
number or any expression that
evaluates to a real number.
Syntax
Expression, p. 1-671
You can enter in dividend any real Expression, p. 1-671
number or any expression that
evaluates to a real number.
You can enter in divisor any real
number except zero or any
expression that evaluates to a
real number other than zero.
Expression, p. 1-671
You can enter in exponent any
real number or any expression
that evaluates to a real number.
Expression, p. 1-671
You can enter in index any real
number except zero or any
expression that evaluates to a
real number other than zero.
Expression, p. 1-671
(1 of 3)
SQL Statements 1-685
Expression
Element
Purpose
num_expression A numeric expression for which
an absolute value is to be
returned. The expression serves
as the argument for the ABS
function. See “ABS Function” on
page 1-687 for further
information on num_expression.
radicand
An expression whose root value
is to be returned. The radicand
value is the first argument that is
supplied to the ROOT function.
See “ROOT Function” on
page 1-688 for further
information on radicand.
rounding factor The number of digits to which a
numeric expression is to be
rounded. The rounding factor
value is the second argument
that is supplied to the ROUND
function. The default value of
rounding factor is zero. This
default means that the numeric
expression is rounded to zero
digits or the ones place. See
“ROUND Function” on
page 1-688 for further
information on rounding factor.
sqrt_radicand
An expression whose square
root value is to be returned. The
sqrt_radicand value is the
argument that is supplied to the
SQRT function. See “SQRT
Function” on page 1-689 for
further information on
sqrt_radicand.
Restrictions
Syntax
The value of num_expression can Expression, p. 1-671
be any real number.
You can enter in radicand any real Expression, p. 1-671
number or any expression that
evaluates to a real number.
The value you specify in
rounding factor must be an
integer between +32 and -32,
inclusive. See “ROUND
Function” on page 1-688 for
further information on this
restriction.
Literal Number,
p. 1-752
You can enter in sqrt_radicand
any real number or any
expression that evaluates to a
real number.
Expression, p. 1-671
(2 of 3)
1-686
Informix Guide to SQL: Syntax
Expression
Element
truncating
factor
Purpose
The position to which a numeric
expression is to be truncated.
The truncating factor value is the
second argument that is
supplied to the TRUNC
function.The default value of
truncating factor is zero. This
default means that the numeric
expression is truncated to zero
digits or the ones place. See
“TRUNC Function” on
page 1-690 for further
information on truncating factor.
Restrictions
The value you specify in
truncating factor must be an
integer between +32 and -32,
inclusive. See “TRUNC
Function” on page 1-690 for
further information on this
restriction.
Syntax
Literal Number,
p. 1-752
(3 of 3)
ABS Function
The ABS function gives the absolute value for a given expression. The
function requires a single numeric argument. The value returned is the same
as the argument type. The following example shows all orders of more than
$20 paid in cash (+) or store credit (-). The stores7 database does not contain
any negative balances; however, you might have negative balances in your
application.
SELECT order_num, customer_num, ship_charge
FROM orders WHERE ABS(ship_charge) > 20
MOD Function
The MOD function returns the modulus or remainder value for two numeric
expressions. You provide integer expressions for the dividend and divisor.
The divisor cannot be 0. The value returned is INT. The following example
uses a 30-day billing cycle to determine how far into the billing cycle today is:
SELECT MOD(today - MDY(1,1,year(today)),30) FROM orders
SQL Statements 1-687
Expression
POW Function
The POW function raises the base to the exponent. This function requires two
numeric arguments. The return type is FLOAT. The following example
returns all the information for circles whose areas ( π r2) are less than
1,000 square units:
SELECT * FROM circles WHERE (3.1417 * POW(radius,2)) < 1000
ROOT Function
The ROOT function returns the root value of a numeric expression. This
function requires at least one numeric argument (the radicand argument) and
allows no more than two (the radicand and index arguments). If only the
radicand argument is supplied, the value 2 is used as a default value for the
index argument. The value 0 cannot be used as the value of index. The value
that the ROOT function returns is FLOAT. The first SELECT statement in the
following example takes the square root of the expression. The second
SELECT statement takes the cube root of the expression.
SELECT ROOT(9) FROM angles
-- square root of 9
SELECT ROOT(64,3) FROM angles
-- cube root of 64
The SQRT function uses the form SQRT(x)=ROOT(x) if no index is given.
ROUND Function
The ROUND function returns the rounded value of an expression. The
expression must be numeric or must be converted to numeric.
If you omit the digit indication, the value is rounded to zero digits or to the
ones place. The digit limitation of 32 (+ and -) refers to the entire decimal
value.
1-688
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Expression
TRUNC Function
The TRUNC function returns the truncated value of a numeric expression.
The expression must be numeric or a form that can be converted to a numeric
expression. If you omit the digit indication, the value is truncated to zero
digits or to the one’s place. The digit limitation of 32 (+ and -) refers to the
entire decimal value.
Positive digit values indicate truncating to the right of the decimal point;
negative digit values indicate truncating to the left of the decimal point, as
Figure 1-5 shows.
Figure 1-5
TRUNC Function
24536.8746
Expression:
TRUNC (24536.8746, -2) =24500
TRUNC (24536.8746, 0) = 24536
TRUNC (24536.8746, 2) = 24536.87
-2
0
2
If you use a MONEY data type as the argument for the TRUNC function and
you truncate to zero places, the .00 places are removed. For example, the
following SELECT statement truncates a MONEY value and an INTEGER
value. It displays 125 and a truncated price in integer format for each row in
items.
SELECT TRUNC(125.46), TRUNC(total_price) FROM items
DBINFO Function
Use the DBINFO function for any of the following purposes:
1-690
■
To locate the name of a dbspace corresponding to a tblspace number
or expression
■
To find out the last serial value inserted in a table
■
To find out the number of rows processed by selects, inserts, deletes,
updates, and execute procedure statements
■
To find out the session ID of the current session
Informix Guide to SQL: Syntax
Expression
You can use the DBINFO function anywhere within SQL statements and
within stored procedures.
DBINFO Function
DBINFO
(
OL
'DBSPACE'
,
tblspace num
)
expression
'sqlca.sqlerrd1'
'sqlca.sqlerrd2'
OL
+
'sessionid'
Element
expression
tblspace num
Purpose
An expression that evaluates to
tblspace num
Restrictions
The expression can contain
procedure variables, host
variables, column names, or
subqueries, but it must evaluate
to a numeric value.
The tblspace number (partition The specified tblspace number
number) of a table. The DBSPACE must exist. That is, it must occur
option of the DBINFO function
in the partnum column of the
returns the name of the dbspace systables table for the database.
that corresponds to the specified
tblspace number.
Syntax
Expression, p. 1-671
Literal Number,
p. 1-752
Using the 'DBSPACE' Option
The 'DBSPACE' option returns a character string that contains the name of the
dbspace corresponding to a tblspace number. You must supply an additional
parameter, either tblspace num or an expression that evaluates to tblspace num.
The following example uses the 'DBSPACE' option. First, it queries the
systables system catalog table to determine the tblspace num for the table
customer, then it executes the function to determine the dbspace name.
SELECT tabname, partnum FROM systables;
SQL Statements 1-691
Expression
If the statement returns a partition number of 16777289, you insert that value
into the second argument to find which dbspace contains the customer table,
as shown in the following example:
SELECT DBINFO ('DBSPACE', 16777289) FROM systables;
Using the 'sqlca.sqlerrd1' Option
The 'sqlca.sqlerrd1' option returns a single integer that provides the last serial
value that is inserted into a table. To ensure valid results, use this option
immediately following an INSERT statement that inserts a serial value. The
following example uses the 'sqlca.sqlerrd1' option:
.
.
EXEC SQL create table fst_tab (ordernum serial, partnum int);
EXEC SQL create table sec_tab (ordernum serial);
EXEC SQL insert into fst_tab VALUES (0,1);
EXEC SQL insert into fst_tab VALUES (0,4);
EXEC SQL insert into fst_tab VALUES (0,6);
EXEC SQL insert into sec_tab
select dbinfo('sqlca.sqlerrd1')
from sec_tab where partnum = 6;
.
.
This example inserts a row that contains a primary-key serial value into the
fst_tab table, and then uses the DBINFO() function to insert the same serial
value into the sec_tab table. The value that the DBINFO() function returns is
the serial value of the last row that is inserted into fst_tab. The subquery in
the last line contains a WHERE clause so that a single value is returned.
Using the 'sqlca.sqlerrd2' Option
The 'sqlca.sqlerrd2' option returns a single integer that provides the number
of rows that SELECT, INSERT, DELETE, UPDATE, and EXECUTE PROCEDURE
statements processed. To ensure valid results, use this option after SELECT
and EXECUTE PROCEDURE statements have completed executing. In
addition, if you use this option within cursors, make sure that all rows are
fetched before the cursors are closed to ensure valid results.
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Informix Guide to SQL: Syntax
Expression
The following example shows a stored procedure that uses the
'sqlca.sqlerrd2' option to determine the number of rows that are deleted from
a table:
CREATE PROCEDURE del_rows (pnumb int)
RETURNING int;
DEFINE nrows int;
DELETE FROM sec_tab WHERE partnum=pnumb;
LET nrows = DBINFO('sqlca.sqlerrd2');
RETURN nrows;
END PROCEDURE
Using the 'sessionid' Option
The 'sessionid' option of the DBINFO function returns the session ID of your
current session.
When a client application makes a connection to INFORMIX-OnLine Dynamic
Server, the database server starts a session with the client and assigns a
session ID for the client. The session ID serves as a unique identifier for a
given connection between a client and a database server. The database server
stores the value of the session ID in a data structure in shared memory that is
called the session control block. The session control block for a given session
also includes the user ID, the process ID of the client, the name of the host
computer, and a variety of status flags.
When you specify the 'sessionid' option, the database server retrieves the
session ID of your current session from the session control block and returns
this value to you as an integer. Some of the System-Monitoring Interface
(SMI) tables in the sysmaster database include a column for session IDs, so
you can use the session ID that the DBINFO function obtained to extract information about your own session from these SMI tables. For further information on the session control block, the sysmaster database, and the SMI
tables, see the INFORMIX-OnLine Dynamic Server Administrator’s Guide.
SQL Statements 1-693
Expression
In the following example, the user specifies the DBINFO function in a SELECT
statement to obtain the value of the current session ID. The user poses this
query against the systables system catalog table and uses a WHERE clause to
limit the query result to a single row.
SELECT DBINFO('sessionid') AS my_sessionid
FROM systables
WHERE tabname = 'systables'
The following table shows the result of this query.
my_sessionid
14
In the preceding example, the SELECT statement queries against the systables
system catalog table. However, you can obtain the session ID of the current
session by querying against any system catalog table or user table in the
database. For example, you can enter the following query to obtain the
session ID of your current session:
SELECT DBINFO('sessionid') AS user_sessionid
FROM customer
where customer_num = 101
The following table shows the result of this query.
user_sessionid
14
You can use the DBINFO function not only in SQL statements but also in
stored procedures. The following example shows a stored procedure that
returns the value of the current session ID to the calling program or
procedure:
CREATE PROCEDURE get_sess()
RETURNING INT;
RETURN DBINFO('sessionid');
END PROCEDURE;
1-694
Informix Guide to SQL: Syntax
Expression
Exponential and Logarithmic Functions
Exponential and logarithmic functions take at least one argument. The return
type is FLOAT. The following example shows exponential and logarithmic
functions.
Exponential and Logarithmic Functions
float expression
LOGN
(
(
float expression
)
)
LOG10
(
float expression
)
EXP
Element
float expression
Purpose
An expression that serves as an
argument to the EXP, LOGN, or
LOG10 functions. For information on the meaning of float
expression in these functions, see
the individual heading for each
function on the following pages.
Restrictions
Syntax
The domain of the expression is Expression, p. 1-671
the set of real numbers, and the
range of the expression is the set
of positive real numbers.
EXP Function
The EXP function returns the exponential value of two numeric expressions.
You provide a constant and float expression in the form e(n)=en. The
following example returns the exponent of 3 for each row of the angles table:
SELECT EXP(3) FROM angles
LOGN Function
The LOGN function returns the natural log of a numeric expression. The
logarithmic value is the inverse of the exponential value. The following
SELECT statement returns the natural log of population for each row of the
history table:
SELECT LOGN(population) FROM history WHERE country='US'
ORDER BY date
SQL Statements 1-695
Expression
LOG10 Function
The LOG10 function returns the log of a value to the base 10. The following
example returns the log base 10 of distance for each row of the travel table:
SELECT LOG10(distance) + 1 digits FROM travel
HEX Function
HEX Function
HEX
Element
integer
expression
Purpose
A numeric expression for which
you want to know the
hexadecimal equivalent
(
integer
expression
)
Restrictions
You must specify an integer or
an expression that evaluates to
an integer.
Syntax
Expression, p. 1-671
The HEX function returns the hexadecimal encoding of an integer expression.
The following example displays the data type and column length of the
columns of the orders table in hexadecimal format. For MONEY and
DECIMAL columns, you can then determine the precision and scale from the
lowest and next-to-the-lowest bytes. For VARCHAR and NVARCHAR
columns, you can determine the minimum space and maximum space from
the lowest and next to the lowest bytes. (See Chapter 2 of the Informix Guide
to SQL: Reference for more information about encoded information.)
SELECT colname, coltype, HEX(collength)
FROM syscolumns C, systables T
WHERE C.tabid = T.tabid AND T.tabname = 'orders'
The following example lists the names of all the tables in the current database
and their corresponding tblspace number in hexadecimal format. This
example is particularly useful because the two most significant bytes in the
hexadecimal number constitute the dbspace number. They are used to
identify the table in oncheck output.
SELECT tabname, HEX(partnum) FROM systables
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Informix Guide to SQL: Syntax
Expression
The HEX function can operate on an expression, as the following example
shows:
SELECT HEX(order_num + 1) FROM orders
Length Functions
LENGTH
Functions
+
LENGTH
CHAR_LENGTH
CHARACTER_LENGTH
OCTET_LENGTH
Quoted
String
p. 1-757
(
SPL
ESQL
Table
Name .
p. 1-768
Element
column name
variable name
Purpose
The name of a column in the
specified table.
A host variable or procedure
variable that contains a character
string.
Restrictions
The column must have a
character data type.
The host variable or procedure
variable must have a character
data type.
)
variable
name
column
name
Syntax
Identifier, p. 1-723
The name of the host
variable must
conform to
language-specific
rules for variable
names. For the
syntax of procedure
variables, see
“Procedure Call
Expressions” on
page 1-722.
You can use length functions to determine the length of a column, string, or
variable. The length functions are LENGTH, OCTET_LENGTH, and
CHAR_LENGTH. Each of these functions has a distinct purpose.
SQL Statements 1-697
Expression
The LENGTH Function
The LENGTH function returns the number of bytes in a character column, not
including any trailing spaces. With TEXT or BYTE columns, the LENGTH
function returns the full number of bytes in the column, including trailing
spaces.
The following example illustrates the use of the LENGTH function:
SELECT customer_num, LENGTH(fname) + LENGTH(lname),
LENGTH('How many bytes is this?')
FROM customer WHERE LENGTH(company) > 10
ESQL
GLS
You can use the LENGTH function to return the length of a character
variable. ♦
For information on GLS aspects of the LENGTH function, see Chapter 3 of the
Guide to GLS Functionality.
The OCTET_LENGTH Function
The OCTET_LENGTH function returns the number of bytes in a character
column, including any trailing spaces. See the Guide to GLS Functionality for
a discussion of the OCTET_LENGTH function.
The CHAR_LENGTH Function
The CHAR_LENGTH function returns the number of characters (not bytes) in
a character column. See the Guide to GLS Functionality for a discussion of the
CHAR_LENGTH function. ♦
1-698
Informix Guide to SQL: Syntax
Expression
Time Functions
Time Functions
+
(
DATE
(
DAY
)
non-date
expression
date/datetime
expression
)
MONTH
WEEKDAY
YEAR
(
EXTEND
date/datetime
expression
)
,
MDY
Element
date/datetime
expression
day integer
expression
first
last
(
month
integer
expression
Purpose
An expression that serves as an
argument in the following
functions: DAY, MONTH,
WEEKDAY, YEAR, and EXTEND
An expression that represents
the number of the day of the
month
,
day
integer
expression
first TO last
,
year
integer
expression
)
Restrictions
Syntax
The expression must evaluate to Expression, p. 1-671
a DATE or DATETIME value.
The expression must evaluate to Expression, p. 1-671
an integer not greater than the
number of days in the specified
month.
A qualifier that specifies the first The qualifier can be any
DATETIME Field
field in the result. If you do not DATETIME qualifier, as long as it Qualifier, p. 1-669
is larger than last.
specify first and last qualifiers,
the default value of first is YEAR.
A qualifier that specifies the last The qualifier can be any
DATETIME Field
field in the result. If you do not DATETIME qualifier, as long as it Qualifier, p. 1-669
is smaller than first.
specify first and last qualifiers,
the default value of last is
FRACTION(3).
(1 of 2)
SQL Statements 1-699
Expression
Element
month integer
expression
non-date
expression
year integer
expression
Purpose
An expression that represents
the number of the month
Restrictions
The expression must evaluate to
an integer between 1 and 12,
inclusive.
An expression whose value is to You can specify any expression
be converted to a DATE data type that can be converted to a DATE
data type. Usually you specify
an expression that evaluates to a
CHAR, DATETIME, or INTEGER
value.
An expression that represents
The expression must evaluate to
the year
a four-digit integer. You cannot
use a two-digit abbreviation.
Syntax
Expression, p. 1-671
Expression, p. 1-671
Expression, p. 1-671
(2 of 2)
DATE Function
The DATE function returns a DATE type value that corresponds to the
non-date expression with which you call it. The argument can be any
expression that can be converted to a DATE value, usually a CHAR,
DATETIME, or INTEGER value. The following WHERE clause specifies a CHAR
value for the non-date expression:
WHERE order_date < DATE('12/31/93')
When the DATE function interprets a CHAR non-date expression, it expects
this expression to conform to any DATE format that the DBDATE environment
specifies. For example, suppose DBDATE is set to Y2MD/ when you execute
the following query:
SELECT DISTINCT DATE('02/01/1995') FROM ship_info
This SELECT statement generates an error because the DATE function cannot
convert this non-date expression. The DATE function interprets the first part
of the date string (02) as the year and the second part (01) as the month. For
the third part (1995), the DATE function encounters four digits when it
expects a two-digit day (valid day values must be between 01 and 31). It
therefore cannot convert the value. For the SELECT statement to execute
successfully with the Y2MD/ value for DBDATE, the non-date expression
would need to be '95/02/01'. For information on the format of DBDATE, see
Chapter 4 of the Informix Guide to SQL: Reference.
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Informix Guide to SQL: Syntax
Expression
When you specify a positive INTEGER value for the non-date expression, the
DATE function interprets the value as the number of days after the default
date of December 31, 1899. If the integer value is negative, the DATE function
interprets the value as the number of days before December 31, 1899. The
following WHERE clause specifies an INTEGER value for the non-date
expression:
WHERE order_date
<
DATE(365)
The database server searches for rows with an order_date value less than
December 31, 1900 (12/31/1899 plus 365 days).
DAY Function
The DAY function returns an integer that represents the day of the month.
The following example uses the DAY function with the CURRENT function to
compare column values to the current day of the month:
WHERE DAY(order_date) > DAY(CURRENT)
MONTH Function
The MONTH function returns an integer that corresponds to the month
portion of its type DATE or DATETIME argument. The following example
returns a number from 1 through 12 to indicate the month when the order
was placed:
SELECT order_num, MONTH(order_date) FROM orders
WEEKDAY Function
The WEEKDAY function returns an integer that represents the day of the
week; zero represents Sunday, one represents Monday, and so on. The
following lists all the orders that were paid on the same day of the week,
which is the current day:
SELECT * FROM orders
WHERE WEEKDAY(paid_date) = WEEKDAY(CURRENT)
SQL Statements 1-701
Expression
YEAR Function
The YEAR function returns a four-digit integer that represents the year. The
following example lists orders in which the ship_date is