Oracle 10g Release 2 database software User's Guide and Reference

Chapter 12, "Using PL/SQL With Object Types" . For information on

You need to delete or update some elements, but not all the elements at once.

■

You would usually create a separate lookup table, with multiple entries for each row of the main table, and access it through join queries.

Nested tables can be sparse: you can delete arbitrary elements, rather than just removing an item from the end.

Nested table data is stored in a separate store table, a system-generated database table associated with the nested table. The database joins the tables for you when you access the nested table. This makes nested tables suitable for queries and updates that only affect some elements of the collection.

You cannot rely on the order and subscripts of a nested table remaining stable as the nested table is stored in and retrieved from the database, because the order and subscripts are not preserved in the database.

Defining Collection Types and Declaring Collection Variables

To create collections, you define a collection type, then declare variables of that type.

Collections follow the same scoping and instantiation rules as other types and variables. Collections are instantiated when you enter a block or subprogram, and cease to exist when you exit. In a package, collections are instantiated when you first reference the package and cease to exist when you end the database session.

Note:

For information on using PL/SQL with SQL object types, see

the

CREATE TYPE

SQL statement, see Oracle Database SQL Reference.

For information on the

CREATE TYPE BODY

SQL statement, see Oracle

Database SQL Reference.

You can define

TABLE

and

VARRAY

types in the declarative part of any PL/SQL block, subprogram, or package using a

TYPE

definition. For the syntax information, see

"Collection Definition" on page 13-17.

For nested tables and varrays declared within PL/SQL, the element type of the table or varray can be any PL/SQL datatype except

REF CURSOR

When defining a

VARRAY

type, you must specify its maximum size with a positive integer. In the following example, you define a type that stores up to 366 dates:

DECLARE

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TYPE Calendar IS VARRAY(366) OF DATE;

Associative arrays (also known as index-by tables) let you insert elements using arbitrary key values. The keys do not have to be consecutive.

The key datatype can be

PLS_INTEGER

BINARY_INTEGER

, or

VARCHAR2

, or one of

VARCHAR2

subtypes

VARCHAR

STRING

, or

LONG

. Note that

PLS_INTEGER

and

BINARY_INTEGER

are identical dataypes.

You must specify the length of a

VARCHAR2

-based key, except for

LONG

which is equivalent to declaring a key type of

VARCHAR2(32760)

. The types

RAW

LONG RAW

ROWID

CHAR

, and

CHARACTER

are not allowed as keys for an associative array. Note that the

LONG

and

LONG RAW

datatypes are supported only for backward

compatibility; see "LONG and LONG RAW Datatypes" on page 3-5 for more

information.

An initialization clause is not allowed. There is no constructor notation for associative arrays. When you reference an element of an associative array that uses a

VARCHAR2

-based key, you can use other types, such as

DATE

TIMESTAMP

, as long as they can be converted to

VARCHAR2

with the

TO_CHAR

function.

Associative arrays can store data using a primary key value as the index, where the key values are not sequential.

Example 5–2 creates a single element in an associative

array, with a subscript of 100 rather than 1.

Example 5–2 Declaring an Associative Array

DECLARE

TYPE EmpTabTyp IS TABLE OF employees%ROWTYPE

INDEX BY PLS_INTEGER;

emp_tab EmpTabTyp;

BEGIN

/* Retrieve employee record. */

SELECT * INTO emp_tab(100) FROM employees WHERE employee_id = 100;

END;

Declaring PL/SQL Collection Variables

After defining a collection type, you declare variables of that type. You use the new type name in the declaration, the same as with predefined types such as

NUMBER

Example 5–3 Declaring Nested Tables, Varrays, and Associative Arrays

DECLARE

TYPE nested_type IS TABLE OF VARCHAR2(30);

TYPE varray_type IS VARRAY(5) OF INTEGER;

TYPE assoc_array_num_type IS TABLE OF NUMBER INDEX BY PLS_INTEGER;

TYPE assoc_array_str_type IS TABLE OF VARCHAR2(32) INDEX BY PLS_INTEGER;

TYPE assoc_array_str_type2 IS TABLE OF VARCHAR2(32) INDEX BY VARCHAR2(64);

v1 nested_type;

v2 varray_type;

v3 assoc_array_num_type;

v4 assoc_array_str_type;

v5 assoc_array_str_type2;

BEGIN

-- an arbitrary number of strings can be inserted v1

v1 := nested_type('Shipping','Sales','Finance','Payroll');

v2 := varray_type(1, 2, 3, 4, 5); -- Up to 5 integers

v3(99) := 10; -- Just start assigning to elements

Using PL/SQL Collections and Records

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Defining Collection Types and Declaring Collection Variables

v3(7) := 100; -- Subscripts can be any integer values

v4(42) := 'Smith'; -- Just start assigning to elements

v4(54) := 'Jones'; -- Subscripts can be any integer values

v5('Canada') := 'North America'; -- Just start assigning to elements

v5('Greece') := 'Europe'; -- Subscripts can be string values

END;

As shown in

Example 5–4

, you can use

%TYPE

to specify the datatype of a previously declared collection, so that changing the definition of the collection automatically updates other variables that depend on the number of elements or the element type.

Example 5–4 Declaring Collections with %TYPE

DECLARE

TYPE few_depts IS VARRAY(10) OF VARCHAR2(30);

TYPE many_depts IS VARRAY(100) OF VARCHAR2(64);

some_depts few_depts;

-- If we change the type of some_depts from few_depts to many_depts,

-- local_depts and global_depts will use the same type

-- when this block is recompiled

local_depts some_depts%TYPE;

global_depts some_depts%TYPE;

BEGIN

NULL;

END;

You can declare collections as the formal parameters of functions and procedures. That way, you can pass collections to stored subprograms and from one subprogram to

another. Example 5–5 declares a nested table as a parameter of a packaged procedure.

Example 5–5 Declaring a Procedure Parameter as a Nested Table

CREATE PACKAGE personnel AS

TYPE staff_list IS TABLE OF employees.employee_id%TYPE;

PROCEDURE award_bonuses (empleos_buenos IN staff_list);

END personnel;

CREATE PACKAGE BODY personnel AS

PROCEDURE award_bonuses (empleos_buenos staff_list) IS

BEGIN

FOR i IN empleos_buenos.FIRST..empleos_buenos.LAST

LOOP

UPDATE employees SET salary = salary + 100

WHERE employees.employee_id = empleos_buenos(i);

END LOOP;

END;

To call personnel.award_bonuses

from outside the package, you declare a variable of type personnel.staff_list

and pass that variable as the parameter.

Example 5–6 Calling a Procedure With a Nested Table Parameter

DECLARE

good_employees personnel.staff_list;

BEGIN

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good_employees := personnel.staff_list(100, 103, 107);

personnel.award_bonuses (good_employees);

END;

You can also specify a collection type in the

RETURN

clause of a function specification.

To specify the element type, you can use

%TYPE

, which provides the datatype of a variable or database column. Also, you can use

%ROWTYPE

, which provides the

rowtype of a cursor or database table. See Example 5–7 and Example 5–8 .

Example 5–7 Specifying Collection Element Types with %TYPE and %ROWTYPE

DECLARE

-- Nested table type that can hold an arbitrary number of employee IDs.

-- The element type is based on a column from the EMPLOYEES table.

-- We do not need to know whether the ID is a number or a string.

TYPE EmpList IS TABLE OF employees.employee_id%TYPE;

-- Declare a cursor to select a subset of columns.

CURSOR c1 IS SELECT employee_id FROM employees;

-- Declare an Array type that can hold information about 10 employees.

-- The element type is a record that contains all the same

-- fields as the EMPLOYEES table.

TYPE Senior_Salespeople IS VARRAY(10) OF employees%ROWTYPE;

-- Declare a cursor to select a subset of columns.

CURSOR c2 IS SELECT first_name, last_name FROM employees;

-- Array type that can hold a list of names. The element type

-- is a record that contains the same fields as the cursor

-- (that is, first_name and last_name).

TYPE NameList IS VARRAY(20) OF c2%ROWTYPE;

BEGIN

NULL;

END;

Example 5–8

uses a

RECORD

type to specify the element type. See

"Defining and

Declaring Records" on page 5-29.

Example 5–8 VARRAY of Records

DECLARE

TYPE name_rec IS RECORD ( first_name VARCHAR2(20), last_name VARCHAR2(25) );

TYPE names IS VARRAY(250) OF name_rec;

BEGIN

NULL;

END;

You can also impose a

NOT NULL

constraint on the element type, as shown in

Example 5–9

Example 5–9 NOT NULL Constraint on Collection Elements

DECLARE

TYPE EmpList IS TABLE OF employees.employee_id%TYPE NOT NULL;

v_employees EmpList := EmpList(100, 150, 160, 200);

BEGIN

v_employees(3) := NULL; -- assigning NULL raises an error

END;

Using PL/SQL Collections and Records

5-9

Initializing and Referencing Collections

Until you initialize it, a nested table or varray is atomically null; the collection itself is null, not its elements. To initialize a nested table or varray, you use a constructor, a system-defined function with the same name as the collection type. This function constructs collections from the elements passed to it.

You must explicitly call a constructor for each varray and nested table variable.

Associative arrays, the third kind of collection, do not use constructors. Constructor calls are allowed wherever function calls are allowed.

Example 5–10 initializes a nested table using a constructor, which looks like a function

with the same name as the collection type:

Example 5–10 Constructor for a Nested Table

DECLARE

TYPE dnames_tab IS TABLE OF VARCHAR2(30);

dept_names dnames_tab;

BEGIN

dept_names := dnames_tab('Shipping','Sales','Finance','Payroll');

END;

Because a nested table does not have a declared size, you can put as many elements in the constructor as necessary.

Example 5–11 initializes a varray using a constructor, which looks like a function with

the same name as the collection type:

Example 5–11 Constructor for a Varray

DECLARE

-- In the varray, we put an upper limit on the number of elements

TYPE dnames_var IS VARRAY(20) OF VARCHAR2(30);

dept_names dnames_var;

BEGIN

-- Because dnames is declared as VARRAY(20), we can put up to 10

-- elements in the constructor

dept_names := dnames_var('Shipping','Sales','Finance','Payroll');

END;

Unless you impose the

NOT NULL

constraint in the type declaration, you can pass null

elements to a constructor as in Example 5–12 .

Example 5–12 Collection Constructor Including Null Elements

DECLARE

TYPE dnames_tab IS TABLE OF VARCHAR2(30);

dept_names dnames_tab;

TYPE dnamesNoNulls_type IS TABLE OF VARCHAR2(30) NOT NULL;

BEGIN

dept_names := dnames_tab('Shipping', NULL,'Finance', NULL);

-- If dept_names was of type dnamesNoNulls_type, we could not include

-- null values in the constructor

END;

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Initializing and Referencing Collections

You can initialize a collection in its declaration, which is a good programming practice, as shown in

Example 5–13

. In this case, you can call the collection's

EXTEND

method to add elements later.

Example 5–13 Combining Collection Declaration and Constructor

DECLARE

TYPE dnames_tab IS TABLE OF VARCHAR2(30);

dept_names dnames_tab := dnames_tab('Shipping','Sales','Finance','Payroll');

BEGIN

NULL;

END;

If you call a constructor without arguments, you get an empty but non-null collection as shown in

Example 5–14

Example 5–14 Empty Varray Constructor

DECLARE

TYPE dnames_var IS VARRAY(20) OF VARCHAR2(30);

dept_names dnames_var;

BEGIN

IF dept_names IS NULL THEN

DBMS_OUTPUT.PUT_LINE('Before initialization, the varray is null.');

-- While the varray is null, we cannot check its COUNT attribute.

-- DBMS_OUTPUT.PUT_LINE('It has ' || dept_names.COUNT || ' elements.');

ELSE

DBMS_OUTPUT.PUT_LINE('Before initialization, the varray is not null.');

END IF;

dept_names := dnames_var(); -- initialize empty varray

IF dept_names IS NULL THEN

DBMS_OUTPUT.PUT_LINE('After initialization, the varray is null.');

ELSE

DBMS_OUTPUT.PUT_LINE('After initialization, the varray is not null.');

DBMS_OUTPUT.PUT_LINE('It has ' || dept_names.COUNT || ' elements.');

END IF;

END;

Referencing Collection Elements

Every reference to an element includes a collection name and a subscript enclosed in parentheses. The subscript determines which element is processed. To reference an element, you specify its subscript using the syntax

collection_name

(subscript) where subscript is an expression that yields an integer in most cases, or a

VARCHAR2

for associative arrays declared with strings as keys.

The allowed subscript ranges are:

■

For nested tables, 1 .. 2147483647 (the upper limit of

PLS_INTEGER

■

For varrays, 1 .. size_limit, where you specify the limit in the declaration (not to exceed 2147483647).

For associative arrays with a numeric key, -2147483648 to 2147483647.

Using PL/SQL Collections and Records

5-11

Assigning Collections

■

For associative arrays with a string key, the length of the key and number of possible values depends on the

VARCHAR2

length limit in the type declaration, and the database character set.

Example 5–15 shows how to reference an element in a nested table.

Example 5–15 Referencing a Nested Table Element

DECLARE

TYPE Roster IS TABLE OF VARCHAR2(15);

names Roster := Roster('D Caruso', 'J Hamil', 'D Piro', 'R Singh');

PROCEDURE verify_name(the_name VARCHAR2) IS

BEGIN

DBMS_OUTPUT.PUT_LINE(the_name);

END;

BEGIN

FOR i IN names.FIRST .. names.LAST

LOOP

IF names(i) = 'J Hamil' THEN

DBMS_OUTPUT.PUT_LINE(names(i)); -- reference to nested table element

END IF;

END LOOP;

verify_name(names(3)); -- procedure call with reference to element

END;

Example 5–16 shows how you can reference the elements of an associative array in a

function call.

Example 5–16 Referencing an Element of an Associative Array

DECLARE

TYPE sum_multiples IS TABLE OF PLS_INTEGER INDEX BY PLS_INTEGER;

n PLS_INTEGER := 5; -- number of multiples to sum for display

sn PLS_INTEGER := 10; -- number of multiples to sum

m PLS_INTEGER := 3; -- multiple

FUNCTION get_sum_multiples(multiple IN PLS_INTEGER, num IN PLS_INTEGER)

RETURN sum_multiples IS

s sum_multiples;

BEGIN

FOR i IN 1..num LOOP

s(i) := multiple * ((i * (i + 1)) / 2) ; -- sum of multiples

END LOOP;

RETURN s;

END get_sum_multiples;

BEGIN

-- call function to retrieve the element identified by subscript (key)

DBMS_OUTPUT.PUT_LINE('Sum of the first ' || TO_CHAR(n) || ' multiples of ' ||

TO_CHAR(m) || ' is ' || TO_CHAR(get_sum_multiples (m, sn)(n)));

END;

Assigning Collections

One collection can be assigned to another by an

INSERT

UPDATE

FETCH

, or

SELECT statement, an assignment statement, or a subprogram call. You can assign the value of an expression to a specific element in a collection using the syntax:

collection_name

(subscript) := expression;

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Assigning Collections where expression yields a value of the type specified for elements in the collection type definition.

You can use operators such as

SET

MULTISET UNION

MULTISET INTERSECT

, and

MULTISET EXCEPT

to transform nested tables as part of an assignment statement.

Assigning a value to a collection element can cause exceptions, such as:

■

If the subscript is

NULL

or is not convertible to the right datatype, PL/SQL raises the predefined exception

VALUE_ERROR

. Usually, the subscript must be an integer.

Associative arrays can also be declared to have

VARCHAR2

subscripts.

■

If the subscript refers to an uninitialized element, PL/SQL raises

SUBSCRIPT_

BEYOND_COUNT

If the collection is atomically null, PL/SQL raises

COLLECTION_IS_NULL

For more information on collection exceptions, see

"Avoiding Collection Exceptions" on page 5-27, Example 5–38 on page 5-27, and

"Summary of Predefined PL/SQL

Exceptions" on page 10-4.

Example 5–17 shows that collections must have the same datatype for an assignment

to work. Having the same element type is not enough.

Example 5–17 Datatype Compatibility for Collection Assignment

DECLARE

TYPE last_name_typ IS VARRAY(3) OF VARCHAR2(64);

TYPE surname_typ IS VARRAY(3) OF VARCHAR2(64);

-- These first two variables have the same datatype.

group1 last_name_typ := last_name_typ('Jones','Wong','Marceau');

group2 last_name_typ := last_name_typ('Klein','Patsos','Singh');

-- This third variable has a similar declaration, but is not the same type.

group3 surname_typ := surname_typ('Trevisi','Macleod','Marquez');

BEGIN

-- Allowed because they have the same datatype

group1 := group2;

-- Not allowed because they have different datatypes

-- group3 := group2; -- raises an error

END;

If you assign an atomically null nested table or varray to a second nested table or

varray, the second collection must be reinitialized, as shown in Example 5–18 . In the

same way, assigning the value

NULL

to a collection makes it atomically null.

Example 5–18 Assigning a Null Value to a Nested Table

DECLARE

TYPE dnames_tab IS TABLE OF VARCHAR2(30);

-- This nested table has some values

dept_names dnames_tab := dnames_tab('Shipping','Sales','Finance','Payroll');

-- This nested table is not initialized ("atomically null").

empty_set dnames_tab;

BEGIN

-- At first, the initialized variable is not null.

if dept_names IS NOT NULL THEN

DBMS_OUTPUT.PUT_LINE('OK, at first dept_names is not null.');

END IF;

-- Then we assign a null nested table to it.

dept_names := empty_set;

-- Now it is null.

Using PL/SQL Collections and Records

5-13

Assigning Collections

if dept_names IS NULL THEN

DBMS_OUTPUT.PUT_LINE('OK, now dept_names has become null.');

END IF;

-- We must use another constructor to give it some values.

dept_names := dnames_tab('Shipping','Sales','Finance','Payroll');

END;

Example 5–19 shows some of the ANSI-standard operators that you can apply to

nested tables.

Example 5–19 Assigning Nested Tables with Set Operators

DECLARE

TYPE nested_typ IS TABLE OF NUMBER;

nt1 nested_typ := nested_typ(1,2,3);

nt2 nested_typ := nested_typ(3,2,1);

nt3 nested_typ := nested_typ(2,3,1,3);

nt4 nested_typ := nested_typ(1,2,4);

answer nested_typ;

-- The results might be in a different order than you expect.

-- Remember, you should not rely on the order of elements in nested tables.

PROCEDURE print_nested_table(the_nt nested_typ) IS

output VARCHAR2(128);

BEGIN

IF the_nt IS NULL THEN

DBMS_OUTPUT.PUT_LINE('Results: <NULL>');

RETURN;

END IF;

IF the_nt.COUNT = 0 THEN

DBMS_OUTPUT.PUT_LINE('Results: empty set');

RETURN;

END IF;

FOR i IN the_nt.FIRST .. the_nt.LAST

LOOP

output := output || the_nt(i) || ' ';

END LOOP;

DBMS_OUTPUT.PUT_LINE('Results: ' || output);

END;

BEGIN

answer := nt1 MULTISET UNION nt4; -- (1,2,3,1,2,4)

print_nested_table(answer);

answer := nt1 MULTISET UNION nt3; -- (1,2,3,2,3,1,3)

print_nested_table(answer);

answer := nt1 MULTISET UNION DISTINCT nt3; -- (1,2,3)

print_nested_table(answer);

answer := nt2 MULTISET INTERSECT nt3; -- (3,2,1)

print_nested_table(answer);

answer := nt2 MULTISET INTERSECT DISTINCT nt3; -- (3,2,1)

print_nested_table(answer);

answer := SET(nt3); -- (2,3,1)

print_nested_table(answer);

answer := nt3 MULTISET EXCEPT nt2; -- (3)

print_nested_table(answer);

answer := nt3 MULTISET EXCEPT DISTINCT nt2; -- ()

print_nested_table(answer);

END;

Example 5–20 shows an assignment to a

VARRAY

of records with an assignment statement.

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Assigning Collections

Example 5–20 Assigning Values to VARRAYs with Complex Datatypes

DECLARE

TYPE emp_name_rec is RECORD (

firstname employees.first_name%TYPE,

lastname employees.last_name%TYPE,

hiredate employees.hire_date%TYPE

);

-- Array type that can hold information 10 employees

TYPE EmpList_arr IS VARRAY(10) OF emp_name_rec;

SeniorSalespeople EmpList_arr;

-- Declare a cursor to select a subset of columns.

CURSOR c1 IS SELECT first_name, last_name, hire_date FROM employees;

Type NameSet IS TABLE OF c1%ROWTYPE;

SeniorTen NameSet;

EndCounter NUMBER := 10;

BEGIN

SeniorSalespeople := EmpList_arr();

SELECT first_name, last_name, hire_date BULK COLLECT INTO SeniorTen FROM

employees WHERE job_id = 'SA_REP' ORDER BY hire_date;

IF SeniorTen.LAST > 0 THEN

IF SeniorTen.LAST < 10 THEN EndCounter := SeniorTen.LAST;

END IF;

FOR i in 1..EndCounter LOOP

SeniorSalespeople.EXTEND(1);

SeniorSalespeople(i) := SeniorTen(i);

DBMS_OUTPUT.PUT_LINE(SeniorSalespeople(i).lastname || ', '

|| SeniorSalespeople(i).firstname || ', ' ||

SeniorSalespeople(i).hiredate);

END LOOP;

END IF;

END;

Example 5–21 shows an assignment to a nested table of records with a

FETCH statement.

Example 5–21 Assigning Values to Tables with Complex Datatypes

DECLARE

TYPE emp_name_rec is RECORD (

firstname employees.first_name%TYPE,

lastname employees.last_name%TYPE,

hiredate employees.hire_date%TYPE

);

-- Table type that can hold information about employees

TYPE EmpList_tab IS TABLE OF emp_name_rec;

SeniorSalespeople EmpList_tab;

-- Declare a cursor to select a subset of columns.

CURSOR c1 IS SELECT first_name, last_name, hire_date FROM employees;

EndCounter NUMBER := 10;

TYPE EmpCurTyp IS REF CURSOR;

emp_cv EmpCurTyp;

BEGIN

OPEN emp_cv FOR SELECT first_name, last_name, hire_date FROM employees

Using PL/SQL Collections and Records

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Comparing Collections

WHERE job_id = 'SA_REP' ORDER BY hire_date;

FETCH emp_cv BULK COLLECT INTO SeniorSalespeople;

CLOSE emp_cv;

-- for this example, display a maximum of ten employees

IF SeniorSalespeople.LAST > 0 THEN

IF SeniorSalespeople.LAST < 10 THEN EndCounter := SeniorSalespeople.LAST;

END IF;

FOR i in 1..EndCounter LOOP

DBMS_OUTPUT.PUT_LINE(SeniorSalespeople(i).lastname || ', '

|| SeniorSalespeople(i).firstname || ', ' || SeniorSalespeople(i).hiredate);

END LOOP;

END IF;

END;

Comparing Collections

You can check whether a collection is null. Comparisons such as greater than, less than, and so on are not allowed. This restriction also applies to implicit comparisons.

For example, collections cannot appear in a

DISTINCT

GROUP BY

, or

ORDER BY

list.

If you want to do such comparison operations, you must define your own notion of what it means for collections to be greater than, less than, and so on, and write one or more functions to examine the collections and their elements and return a true or false value.

For nested tables, you can check whether two nested table of the same declared type

are equal or not equal, as shown in Example 5–23 . You can also apply set operators

(

CARDINALITY

MEMBER OF

IS A SET

IS EMPTY

) to check certain conditions within a nested table or between two nested tables, as shown in

Example 5–24

Because nested tables and varrays can be atomically null, they can be tested for nullity, as shown in

Example 5–22

Example 5–22 Checking if a Collection Is Null

DECLARE

TYPE emp_name_rec is RECORD (

firstname employees.first_name%TYPE,

lastname employees.last_name%TYPE,

hiredate employees.hire_date%TYPE

);

TYPE staff IS TABLE OF emp_name_rec;

members staff;

BEGIN

-- Condition yields TRUE because we have not used a constructor.

IF members IS NULL THEN

DBMS_OUTPUT.PUT_LINE('NULL');

ELSE

DBMS_OUTPUT.PUT_LINE('Not NULL');

END IF;

END;

Example 5–23 shows that nested tables can be compared for equality or inequality.

They cannot be ordered, because there is no greater than or less than comparison.

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Example 5–23 Comparing Two Nested Tables

DECLARE

TYPE dnames_tab IS TABLE OF VARCHAR2(30);

dept_names1 dnames_tab := dnames_tab('Shipping','Sales','Finance','Payroll');

dept_names2 dnames_tab := dnames_tab('Sales','Finance','Shipping','Payroll');

dept_names3 dnames_tab := dnames_tab('Sales','Finance','Payroll');

BEGIN

-- We can use = or !=, but not < or >.

-- Notice that these 2 are equal even though the members are in different order.

IF dept_names1 = dept_names2 THEN

DBMS_OUTPUT.PUT_LINE('dept_names1 and dept_names2 have the same members.');

END IF;

IF dept_names2 != dept_names3 THEN

DBMS_OUTPUT.PUT_LINE('dept_names2 and dept_names3 have different members.');

END IF;

END;

You can test certain properties of a nested table, or compare two nested tables, using

ANSI-standard set operations, as shown in

Example 5–24 .

Example 5–24 Comparing Nested Tables with Set Operators

DECLARE

TYPE nested_typ IS TABLE OF NUMBER;

nt1 nested_typ := nested_typ(1,2,3);

nt2 nested_typ := nested_typ(3,2,1);

nt3 nested_typ := nested_typ(2,3,1,3);

nt4 nested_typ := nested_typ(1,2,4);

answer BOOLEAN;

howmany NUMBER;

PROCEDURE testify(truth BOOLEAN DEFAULT NULL, quantity NUMBER DEFAULT NULL) IS

BEGIN

IF truth IS NOT NULL THEN

DBMS_OUTPUT.PUT_LINE(CASE truth WHEN TRUE THEN 'True' WHEN FALSE THEN

'False' END);

END IF;

IF quantity IS NOT NULL THEN

DBMS_OUTPUT.PUT_LINE(quantity);

END IF;

END;

BEGIN

answer := nt1 IN (nt2,nt3,nt4); -- true, nt1 matches nt2

testify(truth => answer);

answer := nt1 SUBMULTISET OF nt3; -- true, all elements match

testify(truth => answer);

answer := nt1 NOT SUBMULTISET OF nt4; -- also true

testify(truth => answer);

howmany := CARDINALITY(nt3); -- number of elements in nt3

testify(quantity => howmany);

howmany := CARDINALITY(SET(nt3)); -- number of distinct elements

testify(quantity => howmany);

answer := 4 MEMBER OF nt1; -- false, no element matches

testify(truth => answer);

answer := nt3 IS A SET; -- false, nt3 has duplicates

testify(truth => answer);

answer := nt3 IS NOT A SET; -- true, nt3 has duplicates

testify(truth => answer);

answer := nt1 IS EMPTY; -- false, nt1 has some members

testify(truth => answer);

Using PL/SQL Collections and Records

5-17

Using Multilevel Collections

END;

Using Multilevel Collections

In addition to collections of scalar or object types, you can also create collections whose elements are collections. For example, you can create a nested table of varrays, a varray of varrays, a varray of nested tables, and so on.

When creating a nested table of nested tables as a column in SQL, check the syntax of the

CREATE TABLE

statement to see how to define the storage table.

Example 5–25 , Example 5–26 , and

Example 5–27 are some examples showing the

syntax and possibilities for multilevel collections. See also

Example 12–17, "Using

BULK COLLECT with Nested Tables" on page 12-11.

Example 5–25 Multilevel VARRAY

DECLARE

TYPE t1 IS VARRAY(10) OF INTEGER;

TYPE nt1 IS VARRAY(10) OF t1; -- multilevel varray type

va t1 := t1(2,3,5);

-- initialize multilevel varray

nva nt1 := nt1(va, t1(55,6,73), t1(2,4), va);

i INTEGER;

va1 t1;

BEGIN

-- multilevel access

i := nva(2)(3); -- i will get value 73

DBMS_OUTPUT.PUT_LINE('I = ' || i);

-- add a new varray element to nva

nva.EXTEND;

-- replace inner varray elements

nva(5) := t1(56, 32);

nva(4) := t1(45,43,67,43345);

-- replace an inner integer element

nva(4)(4) := 1; -- replaces 43345 with 1

-- add a new element to the 4th varray element

-- and store integer 89 into it.

nva(4).EXTEND;

nva(4)(5) := 89;

END;

Example 5–26 Multilevel Nested Table

DECLARE

TYPE tb1 IS TABLE OF VARCHAR2(20);

TYPE Ntb1 IS TABLE OF tb1; -- table of table elements

TYPE Tv1 IS VARRAY(10) OF INTEGER;

TYPE ntb2 IS TABLE OF tv1; -- table of varray elements

vtb1 tb1 := tb1('one', 'three');

vntb1 ntb1 := ntb1(vtb1);

vntb2 ntb2 := ntb2(tv1(3,5), tv1(5,7,3)); -- table of varray elements

BEGIN

vntb1.EXTEND;

vntb1(2) := vntb1(1);

-- delete the first element in vntb1

vntb1.DELETE(1);

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Using Collection Methods

-- delete the first string from the second table in the nested table

vntb1(2).DELETE(1);

END;

Example 5–27 Multilevel Associative Array

DECLARE

TYPE tb1 IS TABLE OF INTEGER INDEX BY PLS_INTEGER;

-- the following is index-by table of index-by tables

TYPE ntb1 IS TABLE OF tb1 INDEX BY PLS_INTEGER;

TYPE va1 IS VARRAY(10) OF VARCHAR2(20);

-- the following is index-by table of varray elements

TYPE ntb2 IS TABLE OF va1 INDEX BY PLS_INTEGER;

v1 va1 := va1('hello', 'world');

v2 ntb1;

v3 ntb2;

v4 tb1;

v5 tb1; -- empty table

BEGIN

v4(1) := 34;

v4(2) := 46456;

v4(456) := 343;

v2(23) := v4;

v3(34) := va1(33, 456, 656, 343);

-- assign an empty table to v2(35) and try again

v2(35) := v5;

v2(35)(2) := 78; -- it works now

END;

Using Collection Methods

Collection methods make collections easier to use, and make your applications easier to maintain. These methods include

COUNT

DELETE

EXISTS

EXTEND

FIRST

LAST

LIMIT

PRIOR

, and

TRIM

A collection method is a built-in function or procedure that operates on collections and is called using dot notation. The following apply to collection methods:

■

Collection methods cannot be called from SQL statements.

EXTEND

and

TRIM

cannot be used with associative arrays.

■

EXISTS

COUNT

LIMIT

FIRST

LAST

PRIOR

, and

are functions;

EXTEND

TRIM

, and

DELETE

are procedures.

EXISTS

PRIOR

TRIM

EXTEND

, and

DELETE

take parameters corresponding to collection subscripts, which are usually integers but can also be strings for associative arrays.

■

Only

EXISTS

can be applied to atomically null collections. If you apply another method to such collections, PL/SQL raises

COLLECTION_IS_NULL

For more information, see

"Collection Methods" on page 13-20.

Checking If a Collection Element Exists (EXISTS Method)

EXISTS(n)

returns

TRUE

if the nth element in a collection exists. Otherwise,

EXISTS(n)

returns

FALSE

. By combining

EXISTS

with

DELETE

, you can work with

Using PL/SQL Collections and Records

5-19

Using Collection Methods sparse nested tables. You can also use

EXISTS

to avoid referencing a nonexistent element, which raises an exception. When passed an out-of-range subscript,

EXISTS returns

FALSE

instead of raising

SUBSCRIPT_OUTSIDE_LIMIT

Example 5–28 Checking Whether a Collection Element EXISTS

DECLARE

TYPE NumList IS TABLE OF INTEGER;

n NumList := NumList(1,3,5,7);

BEGIN

n.DELETE(2); -- Delete the second element

IF n.EXISTS(1) THEN

DBMS_OUTPUT.PUT_LINE('OK, element #1 exists.');

END IF;

IF n.EXISTS(2) = FALSE THEN

DBMS_OUTPUT.PUT_LINE('OK, element #2 has been deleted.');

END IF;

IF n.EXISTS(99) = FALSE THEN

DBMS_OUTPUT.PUT_LINE('OK, element #99 does not exist at all.');

END IF;

END;

Counting the Elements in a Collection (COUNT Method)

COUNT

returns the number of elements that a collection currently contains.

Example 5–29 Counting Collection Elements With COUNT

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(2,4,6,8); -- Collection starts with 4 elements.

BEGIN

DBMS_OUTPUT.PUT_LINE('There are ' || n.COUNT || ' elements in N.');

n.EXTEND(3); -- Add 3 new elements at the end.

DBMS_OUTPUT.PUT_LINE('Now there are ' || n.COUNT || ' elements in N.');

n := NumList(86,99); -- Assign a completely new value with 2 elements.

DBMS_OUTPUT.PUT_LINE('Now there are ' || n.COUNT || ' elements in N.');

n.TRIM(2); -- Remove the last 2 elements, leaving none.

DBMS_OUTPUT.PUT_LINE('Now there are ' || n.COUNT || ' elements in N.');

END;

COUNT

is useful because the current size of a collection is not always known. For example, you can fetch a column of Oracle data into a nested table, where the number of elements depends on the size of the result set.

For varrays,

COUNT

always equals

LAST

. You can increase or decrease the size of a varray using the

EXTEND

and

TRIM

methods, so the value of

COUNT

can change, up to the value of the

LIMIT

method.

For nested tables,

COUNT

normally equals

LAST

. But, if you delete elements from the middle of a nested table,

COUNT

becomes smaller than

LAST

. When tallying elements,

COUNT

ignores deleted elements. Using

DELETE

with no parameters sets

COUNT

to 0.

Checking the Maximum Size of a Collection (LIMIT Method)

For nested tables and associative arrays, which have no declared size,

LIMIT

returns

NULL

. For varrays,

LIMIT

returns the maximum number of elements that a varray can

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Using Collection Methods contain. You specify this limit in the type definition, and can change it later with the

TRIM

and

EXTEND

methods.

Example 5–30 Checking the Maximum Size of a Collection With LIMIT

DECLARE

TYPE dnames_var IS VARRAY(7) OF VARCHAR2(30);

dept_names dnames_var := dnames_var('Shipping','Sales','Finance','Payroll');

BEGIN

DBMS_OUTPUT.PUT_LINE('dept_names has ' || dept_names.COUNT

|| ' elements now');

DBMS_OUTPUT.PUT_LINE('dept_names''s type can hold a maximum of '

|| dept_names.LIMIT || ' elements');

DBMS_OUTPUT.PUT_LINE('The maximum number you can use with '

|| 'dept_names.EXTEND() is ' || (dept_names.LIMIT - dept_names.COUNT));

END;

Finding the First or Last Collection Element (FIRST and LAST Methods)

FIRST

and

LAST

return the first and last (smallest and largest) index numbers in a collection that uses integer subscripts.

For an associative array with

VARCHAR2

key values, the lowest and highest key values are returned. By default, the order is based on the binary values of the characters in the string. If the

NLS_COMP

initialization parameter is set to

ANSI

, the order is based on the locale-specific sort order specified by the

NLS_SORT

initialization parameter.

If the collection is empty,

FIRST

and

LAST

return

NULL

. If the collection contains only one element,

FIRST

and

LAST

return the same index value.

Example 5–31 shows how to use

FIRST

and

LAST

to iterate through the elements in a collection that has consecutive subscripts.

Example 5–31 Using FIRST and LAST With a Collection

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(1,3,5,7);

counter INTEGER;

BEGIN

DBMS_OUTPUT.PUT_LINE('N''s first subscript is ' || n.FIRST);

DBMS_OUTPUT.PUT_LINE('N''s last subscript is ' || n.LAST);

-- When the subscripts are consecutive starting at 1,

-- it's simple to loop through them.

FOR i IN n.FIRST .. n.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Element #' || i || ' = ' || n(i));

END LOOP;

n.DELETE(2); -- Delete second element.

-- When the subscripts have gaps or the collection might be uninitialized,

-- the loop logic is more extensive. We start at the first element, and

-- keep looking for the next element until there are no more.

IF n IS NOT NULL THEN

counter := n.FIRST;

WHILE counter IS NOT NULL

LOOP

DBMS_OUTPUT.PUT_LINE('Element #' || counter || ' = ' || n(counter));

counter := n.NEXT(counter);

END LOOP;

ELSE

Using PL/SQL Collections and Records

5-21

Using Collection Methods

DBMS_OUTPUT.PUT_LINE('N is null, nothing to do.');

END IF;

END;

For varrays,

FIRST

always returns 1 and

LAST

always equals

COUNT

For nested tables, normally

FIRST

returns 1 and

LAST

equals

COUNT

. But if you delete elements from the beginning of a nested table,

FIRST

returns a number larger than 1.

If you delete elements from the middle of a nested table,

LAST

becomes larger than

COUNT

When scanning elements,

FIRST

and

LAST

ignore deleted elements.

Looping Through Collection Elements (PRIOR and NEXT Methods)

PRIOR

( n

) returns the index number that precedes index n

in a collection.

NEXT(n) returns the index number that succeeds index n

. If n

has no predecessor,

PRIOR(n) returns

NULL

. If n

has no successor,

NEXT(n)

returns

NULL

For associative arrays with

VARCHAR2

keys, these methods return the appropriate key value; ordering is based on the binary values of the characters in the string, unless the

NLS_COMP

initialization parameter is set to

ANSI

, in which case the ordering is based on the locale-specific sort order specified by the

NLS_SORT

initialization parameter.

These methods are more reliable than looping through a fixed set of subscript values, because elements might be inserted or deleted from the collection during the loop.

This is especially true for associative arrays, where the subscripts might not be in consecutive order and so the sequence of subscripts might be (1,2,4,8,16) or

('A','E','I','O','U').

Example 5–32 Using PRIOR and NEXT to Access Collection Elements

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(1966,1971,1984,1989,1999);

BEGIN

DBMS_OUTPUT.PUT_LINE('The element after #2 is #' || n.NEXT(2));

DBMS_OUTPUT.PUT_LINE('The element before #2 is #' || n.PRIOR(2));

n.DELETE(3); -- Delete an element to show how NEXT can handle gaps.

DBMS_OUTPUT.PUT_LINE('Now the element after #2 is #' || n.NEXT(2));

IF n.PRIOR(n.FIRST) IS NULL THEN

DBMS_OUTPUT.PUT_LINE('Can''t get PRIOR of the first element or NEXT of the last.');

END IF;

END;

You can use

PRIOR

to traverse collections indexed by any series of subscripts.

Example 5–33 uses

to traverse a nested table from which some elements have been deleted.

Example 5–33 Using NEXT to Access Elements of a Nested Table

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(1,3,5,7);

counter INTEGER;

BEGIN

n.DELETE(2); -- Delete second element.

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Using Collection Methods

-- When the subscripts have gaps, the loop logic is more extensive. We start at

-- the first element, and keep looking for the next element until there are no more.

counter := n.FIRST;

WHILE counter IS NOT NULL

LOOP

DBMS_OUTPUT.PUT_LINE('Counting up: Element #' || counter || ' = ' ||

n(counter));

counter := n.NEXT(counter);

END LOOP;

-- Run the same loop in reverse order.

counter := n.LAST;

WHILE counter IS NOT NULL

LOOP

DBMS_OUTPUT.PUT_LINE('Counting down: Element #' || counter || ' = ' ||

n(counter));

counter := n.PRIOR(counter);

END LOOP;

END;

When traversing elements,

PRIOR

and

skip over deleted elements.

Increasing the Size of a Collection (EXTEND Method)

To increase the size of a nested table or varray, use

EXTEND

This procedure has three forms:

■

EXTEND

appends one null element to a collection.

■

EXTEND(n)

appends n

null elements to a collection.

EXTEND(n,i)

appends n

copies of the ith element to a collection.

You cannot use

EXTEND

with index-by tables. You cannot use

EXTEND

to add elements to an uninitialized collection. If you impose the

NOT NULL

constraint on a

TABLE

VARRAY

type, you cannot apply the first two forms of

EXTEND

to collections of that type.

EXTEND

operates on the internal size of a collection, which includes any deleted elements. This refers to deleted elements after using

DELETE(n)

, but not

DELETE without parameters which completely removes all elements. If

EXTEND

encounters deleted elements, it includes them in its tally. PL/SQL keeps placeholders for deleted elements, so that you can re-create them by assigning new values.

Example 5–34 Using EXTEND to Increase the Size of a Collection

DECLARE

TYPE NumList IS TABLE OF INTEGER;

n NumList := NumList(2,4,6,8);

x NumList := NumList(1,3);

PROCEDURE print_numlist(the_list NumList) IS

output VARCHAR2(128);

BEGIN

FOR i IN the_list.FIRST .. the_list.LAST

LOOP

output := output || NVL(TO_CHAR(the_list(i)),'NULL') || ' ';

END LOOP;

DBMS_OUTPUT.PUT_LINE(output);

END;

BEGIN

Using PL/SQL Collections and Records

5-23

Using Collection Methods

DBMS_OUTPUT.PUT_LINE('At first, N has ' || n.COUNT || ' elements.');

n.EXTEND(5); -- Add 5 elements at the end.

DBMS_OUTPUT.PUT_LINE('Now N has ' || n.COUNT || ' elements.');

-- Elements 5, 6, 7, 8, and 9 are all NULL.

print_numlist(n);

DBMS_OUTPUT.PUT_LINE('At first, X has ' || x.COUNT || ' elements.');

x.EXTEND(4,2); -- Add 4 elements at the end.

DBMS_OUTPUT.PUT_LINE('Now X has ' || x.COUNT || ' elements.');

-- Elements 3, 4, 5, and 6 are copies of element #2.

print_numlist(x);

END;

When it includes deleted elements, the internal size of a nested table differs from the values returned by

COUNT

and

LAST

. This refers to deleted elements after using

DELETE(n)

, but not

DELETE

without parameters which completely removes all elements. For instance, if you initialize a nested table with five elements, then delete elements 2 and 5, the internal size is 5,

COUNT

returns 3, and

LAST

returns 4. All deleted elements, regardless of position, are treated alike.

Decreasing the Size of a Collection (TRIM Method)

This procedure has two forms:

■

TRIM

removes one element from the end of a collection.

TRIM(n)

removes n

elements from the end of a collection.

If you want to remove all elements, use

DELETE

without parameters.

For example, this statement removes the last three elements from nested table courses

Example 5–35 Using TRIM to Decrease the Size of a Collection

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(1,2,3,5,7,11);

PROCEDURE print_numlist(the_list NumList) IS

output VARCHAR2(128);

BEGIN

IF n.COUNT = 0 THEN

DBMS_OUTPUT.PUT_LINE('No elements in collection.');

ELSE

FOR i IN the_list.FIRST .. the_list.LAST

LOOP

output := output || NVL(TO_CHAR(the_list(i)),'NULL') || ' ';

END LOOP;

DBMS_OUTPUT.PUT_LINE(output);

END IF;

END;

BEGIN

print_numlist(n);

n.TRIM(2); -- Remove last 2 elements.

print_numlist(n);

n.TRIM; -- Remove last element.

print_numlist(n);

n.TRIM(n.COUNT); -- Remove all remaining elements.

print_numlist(n);

-- If too many elements are specified,

-- TRIM raises the exception SUBSCRIPT_BEYOND_COUNT.

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Using Collection Methods

BEGIN

n := NumList(1,2,3);

n.TRIM(100);

EXCEPTION

WHEN SUBSCRIPT_BEYOND_COUNT THEN

DBMS_OUTPUT.PUT_LINE('I guess there weren''t 100 elements that could be trimmed.');

END;

-- When elements are removed by DELETE, placeholders are left behind. TRIM counts

-- these placeholders as it removes elements from the end.

n := NumList(1,2,3,4);

n.DELETE(3); -- delete element 3

-- At this point, n contains elements (1,2,4).

-- TRIMming the last 2 elements removes the 4 and the placeholder, not 4 and 2.

n.TRIM(2);

print_numlist(n);

END;

If n

is too large,

TRIM(n)

raises

SUBSCRIPT_BEYOND_COUNT

TRIM

operates on the internal size of a collection. If

TRIM

encounters deleted elements, it includes them in its tally. This refers to deleted elements after using

DELETE(n)

, but not

DELETE

without parameters which completely removes all elements.

Example 5–36 Using TRIM on Deleted Elements

DECLARE

TYPE CourseList IS TABLE OF VARCHAR2(10);

courses CourseList;

BEGIN

courses := CourseList('Biol 4412', 'Psyc 3112', 'Anth 3001');

courses.DELETE(courses.LAST); -- delete element 3

/* At this point, COUNT equals 2, the number of valid

elements remaining. So, you might expect the next

statement to empty the nested table by trimming

elements 1 and 2. Instead, it trims valid element 2

and deleted element 3 because TRIM includes deleted

elements in its tally. */

courses.TRIM(courses.COUNT);

DBMS_OUTPUT.PUT_LINE(courses(1)); -- prints 'Biol 4412'

END;

In general, do not depend on the interaction between

TRIM

and

DELETE

. It is better to treat nested tables like fixed-size arrays and use only

DELETE

, or to treat them like stacks and use only

TRIM

and

EXTEND

Because PL/SQL does not keep placeholders for trimmed elements, you cannot replace a trimmed element simply by assigning it a new value.

Deleting Collection Elements (DELETE Method)

This procedure has various forms:

■

DELETE

with no parameters removes all elements from a collection, setting

COUNT to 0.

DELETE(n)

removes the nth element from an associative array with a numeric key or a nested table. If the associative array has a string key, the element corresponding to the key value is deleted. If n

is null,

DELETE(n)

does nothing.

Using PL/SQL Collections and Records

5-25

Using Collection Methods

■

DELETE(m,n)

removes all elements in the range m..n

from an associative array or nested table. If m

is larger than n

or if m

or n

is null,

DELETE(m,n)

does nothing.

For example:

Example 5–37 Using the DELETE Method on a Collection

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n NumList := NumList(10,20,30,40,50,60,70,80,90,100);

TYPE NickList IS TABLE OF VARCHAR2(64) INDEX BY VARCHAR2(32);

nicknames NickList;

BEGIN

n.DELETE(2); -- deletes element 2

n.DELETE(3,6); -- deletes elements 3 through 6

n.DELETE(7,7); -- deletes element 7

n.DELETE(6,3); -- does nothing since 6 > 3

n.DELETE; -- deletes all elements

nicknames('Bob') := 'Robert';

nicknames('Buffy') := 'Esmerelda';

nicknames('Chip') := 'Charles';

nicknames('Dan') := 'Daniel';

nicknames('Fluffy') := 'Ernestina';

nicknames('Rob') := 'Robert';

-- following deletes element denoted by this key

nicknames.DELETE('Chip');

-- following deletes elements with keys in this alphabetic range

nicknames.DELETE('Buffy','Fluffy');

END;

Varrays always have consecutive subscripts, so you cannot delete individual elements except from the end by using the

TRIM

method. You can use

DELETE

without parameters to delete all elements.

If an element to be deleted does not exist,

DELETE(n)

simply skips it; no exception is raised. PL/SQL keeps placeholders for deleted elements, so you can replace a deleted element by assigning it a new value. This refers to deleted elements after using

DELETE(n)

, but not

DELETE

without parameters which completely removes all elements.

DELETE

lets you maintain sparse nested tables. You can store sparse nested tables in the database, just like any other nested tables.

The amount of memory allocated to a nested table can increase or decrease dynamically. As you delete elements, memory is freed page by page. If you delete the entire table, all the memory is freed.

Applying Methods to Collection Parameters

Within a subprogram, a collection parameter assumes the properties of the argument bound to it. You can apply the built-in collection methods (

FIRST

LAST

COUNT

, and so on) to such parameters. You can create general-purpose subprograms that take collection parameters and iterate through their elements, add or delete elements, and so on. For varray parameters, the value of

LIMIT

is always derived from the parameter type definition, regardless of the parameter mode.

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Avoiding Collection Exceptions

Example 5–38 shows various collection exceptions that are predefined in PL/SQL. The

example also includes notes on how to avoid the problems.

Example 5–38 Collection Exceptions

DECLARE

TYPE WordList IS TABLE OF VARCHAR2(5);

words WordList;

err_msg VARCHAR2(100);

PROCEDURE display_error IS

BEGIN

err_msg := SUBSTR(SQLERRM, 1, 100);

DBMS_OUTPUT.PUT_LINE('Error message = ' || err_msg);

END;

BEGIN

words(1) := 10; -- Raises COLLECTION_IS_NULL

-- A constructor has not been used yet.

-- Note: This exception applies to varrays and nested tables,

-- but not to associative arrays which do not need a constructor.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

-- After using a constructor, we can assign values to the elements.

words := WordList('1st', '2nd', '3rd'); -- 3 elements created

-- Any expression that returns a VARCHAR2(5) is valid.

words(3) := words(1) || '+2';

BEGIN

words(3) := 'longer than 5 characters'; -- Raises VALUE_ERROR

-- The assigned value is too long.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words('B') := 'dunno'; -- Raises VALUE_ERROR

-- The subscript (B) of a nested table must be an integer.

-- Note: Also, NULL is not allowed as a subscript.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words(0) := 'zero'; -- Raises SUBSCRIPT_OUTSIDE_LIMIT

-- Subscript 0 is outside the allowed subscript range.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words(4) := 'maybe'; -- Raises SUBSCRIPT_BEYOND_COUNT

-- The subscript (4) exceeds the number of elements in the table.

-- To add new elements, call the EXTEND method first.

EXCEPTION

WHEN OTHERS THEN display_error;

END;

BEGIN

words.DELETE(1);

IF words(1) = 'First' THEN NULL; END IF; -- Raises NO_DATA_FOUND

-- The element with subcript (1) has been deleted.

EXCEPTION

Using PL/SQL Collections and Records

5-27

Avoiding Collection Exceptions

WHEN OTHERS THEN display_error;

END;

Execution continues in

Example 5–38

because the raised exceptions are handled in sub-blocks. See

"Continuing after an Exception Is Raised" on page 10-15. For

information about the use of

SQLERRM

with exception handling, see

"Retrieving the

Error Code and Error Message: SQLCODE and SQLERRM" on page 10-14.

The following list summarizes when a given exception is raised. See also

"Summary of

Predefined PL/SQL Exceptions" on page 10-4.

Collection Exception Raised when...

COLLECTION_IS_NULL

NO_DATA_FOUND

VALUE_ERROR you try to operate on an atomically null collection.

a subscript designates an element that was deleted, or a nonexistent element of an associative array.

SUBSCRIPT_BEYOND_COUNT a subscript exceeds the number of elements in a collection.

SUBSCRIPT_OUTSIDE_LIMIT a subscript is outside the allowed range.

a subscript is null or not convertible to the key type. This exception might occur if the key is defined as a

PLS_

INTEGER

range, and the subscript is outside this range.

In some cases, you can pass invalid subscripts to a method without raising an exception. For instance, when you pass a null subscript to

DELETE(n)

, it does nothing. You can replace deleted elements by assigning values to them, without raising

NO_DATA_FOUND

. This refers to deleted elements after using

DELETE(n)

, but not

DELETE

without parameters which completely removes all elements. For example:

Example 5–39 How Invalid Subscripts are Handled With DELETE(n)

DECLARE

TYPE NumList IS TABLE OF NUMBER;

nums NumList := NumList(10,20,30); -- initialize table

BEGIN

nums.DELETE(-1); -- does not raise SUBSCRIPT_OUTSIDE_LIMIT

nums.DELETE(3); -- delete 3rd element

DBMS_OUTPUT.PUT_LINE(nums.COUNT); -- prints 2

nums(3) := 30; -- allowed; does not raise NO_DATA_FOUND

DBMS_OUTPUT.PUT_LINE(nums.COUNT); -- prints 3

END;

Packaged collection types and local collection types are never compatible. For example, suppose you want to call the following packaged procedure:

Example 5–40 Incompatibility Between Package and Local Collection Types

CREATE PACKAGE pkg AS

TYPE NumList IS TABLE OF NUMBER;

PROCEDURE print_numlist (nums NumList);

END pkg;

CREATE PACKAGE BODY pkg AS

PROCEDURE print_numlist (nums NumList) IS

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Defining and Declaring Records

BEGIN

FOR i IN nums.FIRST..nums.LAST LOOP

DBMS_OUTPUT.PUT_LINE(nums(i));

END LOOP;

END;

END pkg;

DECLARE

TYPE NumList IS TABLE OF NUMBER;

n1 pkg.NumList := pkg.NumList(2,4); -- type from the package.

n2 NumList := NumList(6,8); -- local type.

BEGIN

pkg.print_numlist(n1); -- type from pkg is legal

-- The packaged procedure cannot accept a value of the local type (n2)

-- pkg.print_numlist(n2); -- Causes a compilation error.

END;

The second procedure call fails, because the packaged and local

VARRAY

types are incompatible despite their identical definitions.

Defining and Declaring Records

To create records, you define a

RECORD

type, then declare records of that type. You can also create or find a table, view, or PL/SQL cursor with the values you want, and use the

%ROWTYPE

attribute to create a matching record.

You can define

RECORD

types in the declarative part of any PL/SQL block, subprogram, or package. When you define your own

RECORD

type, you can specify a

NOT NULL

constraint on fields, or give them default values. See "Record Definition" on page 13-95.

Example 5–42 and Example 5–42

illustrate record type declarations.

Example 5–41 Declaring and Initializing a Simple Record Type

DECLARE

TYPE DeptRecTyp IS RECORD (

deptid NUMBER(4) NOT NULL := 99,

dname departments.department_name%TYPE,

loc departments.location_id%TYPE,

region regions%ROWTYPE );

dept_rec DeptRecTyp;

BEGIN

dept_rec.dname := 'PURCHASING';

END;

Example 5–42 Declaring and Initializing Record Types

DECLARE

-- Declare a record type with 3 fields.

TYPE rec1_t IS RECORD (field1 VARCHAR2(16), field2 NUMBER, field3 DATE);

-- For any fields declared NOT NULL, we must supply a default value.

TYPE rec2_t IS RECORD (id INTEGER NOT NULL := -1,

name VARCHAR2(64) NOT NULL := '[anonymous]');

-- Declare record variables of the types declared

rec1 rec1_t;

Using PL/SQL Collections and Records

5-29

Defining and Declaring Records

rec2 rec2_t;

-- Declare a record variable that can hold a row from the EMPLOYEES table.

-- The fields of the record automatically match the names and

-- types of the columns.

-- Don't need a TYPE declaration in this case.

rec3 employees%ROWTYPE;

-- Or we can mix fields that are table columns with user-defined fields.

TYPE rec4_t IS RECORD (first_name employees.first_name%TYPE,

last_name employees.last_name%TYPE,

rating NUMBER);

rec4 rec4_t;

BEGIN

-- Read and write fields using dot notation

rec1.field1 := 'Yesterday';

rec1.field2 := 65;

rec1.field3 := TRUNC(SYSDATE-1);

-- We didn't fill in the name field, so it takes the default value declared

DBMS_OUTPUT.PUT_LINE(rec2.name);

END;

To store a record in the database, you can specify it in an

INSERT

UPDATE statement, if its fields match the columns in the table:

You can use

%TYPE

to specify a field type corresponding to a table column type. Your code keeps working even if the column type is changed (for example, to increase the length of a

VARCHAR2

or the precision of a

NUMBER

). Example 5–43

defines

RECORD types to hold information about a department:

Example 5–43 Using %ROWTYPE to Declare a Record

DECLARE

-- Best: use %ROWTYPE instead of specifying each column.

-- Use <cursor>%ROWTYPE instead of <table>%ROWTYPE because

-- we only want some columns.

-- Declaring the cursor doesn't run the query, so no performance hit.

CURSOR c1 IS SELECT department_id, department_name, location_id

FROM departments;

rec1 c1%ROWTYPE;

-- Use <column>%TYPE in field declarations to avoid problems if

-- the column types change.

TYPE DeptRec2 IS RECORD (dept_id departments.department_id%TYPE,

dept_name departments.department_name%TYPE,

dept_loc departments.location_id%TYPE);

rec2 DeptRec2;

-- Final technique, writing out each field name and specifying the type directly,

-- is clumsy and unmaintainable for working with table data.

-- Use only for all-PL/SQL code.

TYPE DeptRec3 IS RECORD (dept_id NUMBER,

dept_name VARCHAR2(14),

dept_loc VARCHAR2(13));

rec3 DeptRec3;

BEGIN

NULL;

END;

PL/SQL lets you define records that contain objects, collections, and other records

(called nested records). However, records cannot be attributes of object types.

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Oracle Database PL/SQL User’s Guide and Reference

Defining and Declaring Records

Using Records as Procedure Parameters and Function Return Values

Records are easy to process using stored procedures because you can pass just one parameter, instead of a separate parameter for each field. For example, you might fetch a table row from the

EMPLOYEES

table into a record, then pass that row as a parameter to a function that computed that employee's vacation allowance or some other abstract value. The function could access all the information about that employee by referring to the fields in the record.

The next example shows how to return a record from a function. To make the record type visible across multiple stored functions and stored procedures, declare the record type in a package specification.

Example 5–44 Returning a Record from a Function

DECLARE

TYPE EmpRecTyp IS RECORD (

emp_id NUMBER(6),

salary NUMBER(8,2));

CURSOR desc_salary RETURN EmpRecTyp IS

SELECT employee_id, salary FROM employees ORDER BY salary DESC;

emp_rec EmpRecTyp;

FUNCTION nth_highest_salary (n INTEGER) RETURN EmpRecTyp IS

BEGIN

OPEN desc_salary;

FOR i IN 1..n LOOP

FETCH desc_salary INTO emp_rec;

END LOOP;

CLOSE desc_salary;

RETURN emp_rec;

END nth_highest_salary;

BEGIN

NULL;

END;

Like scalar variables, user-defined records can be declared as the formal parameters of procedures and functions:

Example 5–45 Using a Record as Parameter to a Procedure

DECLARE

TYPE EmpRecTyp IS RECORD (

emp_id NUMBER(6),

emp_sal NUMBER(8,2) );

PROCEDURE raise_salary (emp_info EmpRecTyp) IS

BEGIN

UPDATE employees SET salary = salary + salary * .10

WHERE employee_id = emp_info.emp_id;

END raise_salary;

BEGIN

NULL;

END;

You can declare and reference nested records. That is, a record can be the component of another record.

Example 5–46 Declaring a Nested Record

DECLARE

Using PL/SQL Collections and Records

5-31

Assigning Values to Records

TYPE TimeTyp IS RECORD ( minutes SMALLINT, hours SMALLINT );

TYPE MeetingTyp IS RECORD (

day DATE,

time_of TimeTyp, -- nested record

dept departments%ROWTYPE, -- nested record representing a table row

place VARCHAR2(20),

purpose VARCHAR2(50) );

meeting MeetingTyp;

seminar MeetingTyp;

BEGIN

-- you can assign one nested record to another if they are of the same datatype

seminar.time_of := meeting.time_of;

END;

Such assignments are allowed even if the containing records have different datatypes.

Assigning Values to Records

To set all the fields in a record to default values, assign to it an uninitialized record of

the same type, as shown in Example 5–47 .

Example 5–47 Assigning Default Values to a Record

DECLARE

TYPE RecordTyp IS RECORD (field1 NUMBER,

field2 VARCHAR2(32) DEFAULT 'something');

rec1 RecordTyp;

rec2 RecordTyp;

BEGIN

-- At first, rec1 has the values we assign.

rec1.field1 := 100; rec1.field2 := 'something else';

-- Assigning an empty record to rec1 resets fields to their default values.

-- Field1 is NULL and field2 is 'something' due to the DEFAULT clause

rec1 := rec2;

DBMS_OUTPUT.PUT_LINE('Field1 = ' || NVL(TO_CHAR(rec1.field1),'<NULL>') || ',

field2 = ' || rec1.field2);

END;

You can assign a value to a field in a record using an assignment statement with dot notation: emp_info.last_name := 'Fields';

Note that values are assigned separately to each field of a record in

Example 5–47 . You

cannot assign a list of values to a record using an assignment statement. There is no constructor-like notation for records.

You can assign values to all fields at once only if you assign a record to another record with the same datatype. Having fields that match exactly is not enough, as shown in

Example 5–48 .

Example 5–48 Assigning All the Fields of a Record in One Statement

DECLARE

-- Two identical type declarations.

TYPE DeptRec1 IS RECORD ( dept_num NUMBER(2), dept_name VARCHAR2(14));

TYPE DeptRec2 IS RECORD ( dept_num NUMBER(2), dept_name VARCHAR2(14));

dept1_info DeptRec1;

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Oracle Database PL/SQL User’s Guide and Reference

Assigning Values to Records

dept2_info DeptRec2;

dept3_info DeptRec2;

BEGIN

-- Not allowed; different datatypes, even though fields are the same.

-- dept1_info := dept2_info;

-- This assignment is OK because the records have the same type.

dept2_info := dept3_info;

END;

You can assign a

%ROWTYPE

record to a user-defined record if their fields match in number and order, and corresponding fields have the same datatypes:

DECLARE

TYPE RecordTyp IS RECORD (last employees.last_name%TYPE,

id employees.employee_id%TYPE);

CURSOR c1 IS SELECT last_name, employee_id FROM employees;

-- Rec1 and rec2 have different types. But because rec2 is based on a %ROWTYPE,

-- we can assign is to rec1 as long as they have the right number of fields and

-- the fields have the right datatypes.

rec1 RecordTyp;

rec2 c1%ROWTYPE;

BEGIN

SELECT last_name, employee_id INTO rec2 FROM employees WHERE ROWNUM < 2;

rec1 := rec2;

DBMS_OUTPUT.PUT_LINE('Employee #' || rec1.id || ' = ' || rec1.last);

END;

You can also use the

SELECT

FETCH

statement to fetch column values into a record.

The columns in the select-list must appear in the same order as the fields in your record.

Example 5–49 Using SELECT INTO to Assign Values in a Record

DECLARE

TYPE RecordTyp IS RECORD (last employees.last_name%TYPE,

id employees.employee_id%TYPE);

rec1 RecordTyp;

BEGIN

SELECT last_name, employee_id INTO rec1 FROM employees WHERE ROWNUM < 2;

DBMS_OUTPUT.PUT_LINE('Employee #' || rec1.id || ' = ' || rec1.last);

END;

Comparing Records

Records cannot be tested for nullity, or compared for equality, or inequality. If you want to make such comparisons, write your own function that accepts two records as parameters and does the appropriate checks or comparisons on the corresponding fields.

Inserting PL/SQL Records into the Database

A PL/SQL-only extension of the

INSERT

statement lets you insert records into database rows, using a single variable of type

RECORD

%ROWTYPE

in the

VALUES clause instead of a list of fields. That makes your code more readable and maintainable.

Using PL/SQL Collections and Records

5-33

Assigning Values to Records

If you issue the

INSERT

through the

FORALL

statement, you can insert values from an entire collection of records. The number of fields in the record must equal the number of columns listed in the

INTO

clause, and corresponding fields and columns must have compatible datatypes. To make sure the record is compatible with the table, you might find it most convenient to declare the variable as the type table_name

%ROWTYPE

Example 5–50 declares a record variable using a

%ROWTYPE

qualifier. You can insert this variable without specifying a column list. The

%ROWTYPE

declaration ensures that the record attributes have exactly the same names and types as the table columns.

Example 5–50 Inserting a PL/SQL Record Using %ROWTYPE

DECLARE

dept_info departments%ROWTYPE;

BEGIN

-- department_id, department_name, and location_id are the table columns

-- The record picks up these names from the %ROWTYPE

dept_info.department_id := 300;

dept_info.department_name := 'Personnel';

dept_info.location_id := 1700;

-- Using the %ROWTYPE means we can leave out the column list

-- (department_id, department_name, and location_id) from the INSERT statement

INSERT INTO departments VALUES dept_info;

END;

Updating the Database with PL/SQL Record Values

A PL/SQL-only extension of the

UPDATE

statement lets you update database rows using a single variable of type

RECORD

%ROWTYPE

on the right side of the

SET clause, instead of a list of fields.

If you issue the

UPDATE

through the

FORALL

statement, you can update a set of rows using values from an entire collection of records. Also with an

UPDATE

statement, you can specify a record in the

RETURNING

clause to retrieve new values into a record. If you issue the

UPDATE

through the

FORALL

statement, you can retrieve new values from a set of updated rows into a collection of records.

The number of fields in the record must equal the number of columns listed in the

SET clause, and corresponding fields and columns must have compatible datatypes.

You can use the keyword

ROW

to represent an entire row, as shown in

Example 5–51

Example 5–51 Updating a Row Using a Record

DECLARE

dept_info departments%ROWTYPE;

BEGIN

-- department_id, department_name, and location_id are the table columns

-- The record picks up these names from the %ROWTYPE.

dept_info.department_id := 300;

dept_info.department_name := 'Personnel';

dept_info.location_id := 1700;

-- The fields of a %ROWTYPE can completely replace the table columns

-- The row will have values for the filled-in columns, and null

-- for any other columns

UPDATE departments SET ROW = dept_info WHERE department_id = 300;

END;

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Oracle Database PL/SQL User’s Guide and Reference

Assigning Values to Records

The keyword

ROW

is allowed only on the left side of a

SET

clause. The argument to

SET ROW

must be a real PL/SQL record, not a subquery that returns a single row. The record can also contain collections or objects.

The

INSERT

UPDATE

, and

DELETE

statements can include a

RETURNING

clause, which returns column values from the affected row into a PL/SQL record variable.

This eliminates the need to

SELECT

the row after an insert or update, or before a delete.

By default, you can use this clause only when operating on exactly one row. When you use bulk SQL, you can use the form

RETURNING BULK COLLECT INTO

to store the results in one or more collections.

Example 5–52 updates the salary of an employee and retrieves the employee's name,

job title, and new salary into a record variable.

Example 5–52 Using the RETURNING Clause with a Record

DECLARE

TYPE EmpRec IS RECORD (last_name employees.last_name%TYPE,

salary employees.salary%TYPE);

emp_info EmpRec;

emp_id NUMBER := 100;

BEGIN

UPDATE employees SET salary = salary * 1.1 WHERE employee_id = emp_id

RETURNING last_name, salary INTO emp_info;

DBMS_OUTPUT.PUT_LINE('Just gave a raise to ' || emp_info.last_name ||

', who now makes ' || emp_info.salary);

ROLLBACK;

END;

Restrictions on Record Inserts and Updates

Currently, the following restrictions apply to record inserts/updates:

■

Record variables are allowed only in the following places:

■

On the right side of the

SET

clause in an

UPDATE

statement

■

In the

VALUES

clause of an

INSERT

statement

In the

INTO

subclause of a

RETURNING

clause

Record variables are not allowed in a

SELECT

list,

WHERE

clause,

GROUP BY

clause, or

ORDER BY

clause.

The keyword

ROW

is allowed only on the left side of a

SET

clause. Also, you cannot use

ROW

with a subquery.

In an

UPDATE

statement, only one

SET

clause is allowed if

ROW

is used.

If the

VALUES

clause of an

INSERT

statement contains a record variable, no other variable or value is allowed in the clause.

If the

INTO

subclause of a

RETURNING

clause contains a record variable, no other variable or value is allowed in the subclause.

The following are not supported:

■

Nested record types

■

Functions that return a record

Record inserts and updates using the

EXECUTE IMMEDIATE

statement.

Using PL/SQL Collections and Records

5-35

Assigning Values to Records

Querying Data into Collections of Records

You can use the

BULK COLLECT

clause with a

SELECT INTO

FETCH

statement to retrieve a set of rows into a collection of records.

Example 5–53 Using BULK COLLECT With a SELECT INTO Statement

DECLARE

TYPE EmployeeSet IS TABLE OF employees%ROWTYPE;

underpaid EmployeeSet; -- Holds set of rows from EMPLOYEES table.

CURSOR c1 IS SELECT first_name, last_name FROM employees;

TYPE NameSet IS TABLE OF c1%ROWTYPE;

some_names NameSet; -- Holds set of partial rows from EMPLOYEES table.

BEGIN

-- With one query, we bring all the relevant data into the collection of records.

SELECT * BULK COLLECT INTO underpaid FROM employees

WHERE salary < 5000 ORDER BY salary DESC;

-- Now we can process the data by examining the collection, or passing it to

-- a separate procedure, instead of writing a loop to FETCH each row.

DBMS_OUTPUT.PUT_LINE(underpaid.COUNT || ' people make less than 5000.');

FOR i IN underpaid.FIRST .. underpaid.LAST

LOOP

DBMS_OUTPUT.PUT_LINE(underpaid(i).last_name || ' makes ' ||

underpaid(i).salary);

END LOOP;

-- We can also bring in just some of the table columns.

-- Here we get the first and last names of 10 arbitrary employees.

SELECT first_name, last_name BULK COLLECT INTO some_names FROM employees

WHERE ROWNUM < 11;

FOR i IN some_names.FIRST .. some_names.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Employee = ' || some_names(i).first_name || ' ' || some_names(i).last_name);

END LOOP;

END;

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Oracle Database PL/SQL User’s Guide and Reference

Performing SQL Operations from PL/SQL

This chapter shows how PL/SQL supports the SQL commands, functions, and operators that let you manipulate Oracle data.

This chapter contains these topics:

■

Overview of SQL Support in PL/SQL

■

Managing Cursors in PL/SQL

Querying Data with PL/SQL

Using Subqueries

Using Cursor Variables (REF CURSORs)

■

Using Cursor Expressions

Overview of Transaction Processing in PL/SQL

Doing Independent Units of Work with Autonomous Transactions

Overview of SQL Support in PL/SQL

By extending SQL, PL/SQL offers a unique combination of power and ease of use. You can manipulate Oracle data flexibly and safely because PL/SQL fully supports all SQL data manipulation statements (except

EXPLAIN PLAN

), transaction control statements, functions, pseudocolumns, and operators. PL/SQL also conforms to the current

ANSI/ISO SQL standard.

In addition to static SQL discussed in this chapter, PL/SQL also supports dynamic

SQL, which enables you to execute SQL data definition, data control, and session control statements dynamically. See

Chapter 7, "Performing SQL Operations with

Native Dynamic SQL"

Data Manipulation

To manipulate Oracle data you can include DML operations, such as

INSERT

UPDATE

, and

DELETE

statements, directly in PL/SQL programs, without any special notation, as shown in

Example 6–1

. You can also include the SQL

COMMIT

statement directly in a PL/SQL program; see

"Overview of Transaction Processing in PL/SQL" on page 6-30. See also

COMMIT

in the Oracle Database SQL Reference.

Example 6–1 Data Manipulation With PL/SQL

CREATE TABLE employees_temp AS SELECT employee_id, first_name, last_name

FROM employees;

DECLARE

Performing SQL Operations from PL/SQL

6-1

Overview of SQL Support in PL/SQL

emp_id employees_temp.employee_id%TYPE;

emp_first_name employees_temp.first_name%TYPE;

emp_last_name employees_temp.last_name%TYPE;

BEGIN

INSERT INTO employees_temp VALUES(299, 'Bob', 'Henry');

UPDATE employees_temp SET first_name = 'Robert' WHERE employee_id = 299;

DELETE FROM employees_temp WHERE employee_id = 299

RETURNING first_name, last_name INTO emp_first_name, emp_last_name;

COMMIT;

DBMS_OUTPUT.PUT_LINE( emp_first_name || ' ' || emp_last_name);

END;

To find out how many rows are affected by DML statements, you can check the value of

SQL%ROWCOUNT

as shown in

Example 6–2 .

Example 6–2 Checking SQL%ROWCOUNT After an UPDATE

CREATE TABLE employees_temp AS SELECT * FROM employees;

BEGIN

UPDATE employees_temp SET salary = salary * 1.05 WHERE salary < 5000;

DBMS_OUTPUT.PUT_LINE('Updated ' || SQL%ROWCOUNT || ' salaries.');

END;

Wherever you would use literal values, or bind variables in some other programming language, you can directly substitute PL/SQL variables as shown in

Example 6–3 .

Example 6–3 Substituting PL/SQL Variables

CREATE TABLE employees_temp AS SELECT first_name, last_name FROM employees;

DECLARE

x VARCHAR2(20) := 'my_first_name';

y VARCHAR2(25) := 'my_last_name';

BEGIN

INSERT INTO employees_temp VALUES(x, y);

UPDATE employees_temp SET last_name = x WHERE first_name = y;

DELETE FROM employees_temp WHERE first_name = x;

COMMIT;

END;

With this notation, you can use variables in place of values in the

WHERE

clause. To use variables in place of table names, column names, and so on, requires the

EXECUTE

IMMEDIATE

statement that is explained in

"Using the EXECUTE IMMEDIATE

Statement in PL/SQL" on page 7-2.

For information on the use of PL/SQL records with SQL to update and insert data, see

"Inserting PL/SQL Records into the Database" on page 5-33 and

"Updating the

Database with PL/SQL Record Values" on page 5-34.

For additional information on assigning values to PL/SQL variables, see "Assigning a

SQL Query Result to a PL/SQL Variable" on page 2-19.

6-2

Oracle Database PL/SQL User’s Guide and Reference

Overview of SQL Support in PL/SQL

Note:

When issuing a data manipulation (DML) statement in

PL/SQL, there are some situations when the value of a variable is undefined after the statement is executed. These include:

■

If a

FETCH

SELECT

statement raises any exception, then the values of the define variables after that statement are undefined.

■

If a DML statement affects zero rows, the values of the

OUT

binds after the DML executes are undefined. This does not apply to a

BULK

or multirow operation.

Transaction Control

Oracle is transaction oriented; that is, Oracle uses transactions to ensure data integrity.

A transaction is a series of SQL data manipulation statements that does a logical unit of work. For example, two

UPDATE

statements might credit one bank account and debit another. It is important not to allow one operation to succeed while the other fails.

At the end of a transaction that makes database changes, Oracle makes all the changes permanent or undoes them all. If your program fails in the middle of a transaction,

Oracle detects the error and rolls back the transaction, restoring the database to its former state.

You use the

COMMIT

ROLLBACK

SAVEPOINT

, and

SET TRANSACTION

commands to control transactions.

COMMIT

makes permanent any database changes made during the current transaction.

ROLLBACK

ends the current transaction and undoes any changes made since the transaction began.

SAVEPOINT

marks the current point in the processing of a transaction. Used with

ROLLBACK

SAVEPOINT

undoes part of a transaction.

SET TRANSACTION

sets transaction properties such as read-write access and isolation level. See

"Overview of Transaction Processing in PL/SQL" on page 6-30.

SQL Functions

Example 6–4

shows some queries that call SQL functions.

Example 6–4 Calling the SQL COUNT Function in PL/SQL

DECLARE

job_count NUMBER;

emp_count NUMBER;

BEGIN

SELECT COUNT(DISTINCT job_id) INTO job_count FROM employees;

SELECT COUNT(*) INTO emp_count FROM employees;

END;

SQL Pseudocolumns

PL/SQL recognizes the SQL pseudocolumns

CURRVAL

LEVEL

NEXTVAL

ROWID

, and

ROWNUM

. However, there are limitations on the use of pseudocolumns, including the restriction on the use of some pseudocolumns in assignments or conditional tests. For additional information, including restrictions, on the use of SQL pseudocolumns, see

Oracle Database SQL Reference.

Performing SQL Operations from PL/SQL

6-3

Overview of SQL Support in PL/SQL

CURRVAL and NEXTVAL

A sequence is a schema object that generates sequential numbers. When you create a sequence, you can specify its initial value and an increment.

CURRVAL

returns the current value in a specified sequence. Before you can reference

CURRVAL

in a session, you must use

NEXTVAL

to generate a number. A reference to

NEXTVAL

stores the current sequence number in

CURRVAL

NEXTVAL

increments the sequence and returns the next value. To get the current or next value in a sequence, use dot notation: sequence_name.CURRVAL

sequence_name.NEXTVAL

Each time you reference the

NEXTVAL

value of a sequence, the sequence is incremented immediately and permanently, whether you commit or roll back the transaction.

After creating a sequence, you can use it to generate unique sequence numbers for transaction processing. You can use

CURRVAL

and

NEXTVAL

only in a

SELECT

list, the

VALUES

clause, and the

SET

clause.

Example 6–5 shows how to generate a new

sequence number and refer to that same number in more than one statement.

Example 6–5 Using CURRVAL and NEXTVAL

CREATE TABLE employees_temp AS SELECT employee_id, first_name, last_name

FROM employees;

CREATE TABLE employees_temp2 AS SELECT employee_id, first_name, last_name

FROM employees;

DECLARE

seq_value NUMBER;

BEGIN

-- Display initial value of NEXTVAL

-- This is invalid: seq_value := employees_seq.NEXTVAL;

SELECT employees_seq.NEXTVAL INTO seq_value FROM dual;

DBMS_OUTPUT.PUT_LINE ('Initial sequence value: ' || TO_CHAR(seq_value));

-- The NEXTVAL value is the same no matter what table you select from

-- You usually use NEXTVAL to create unique numbers when inserting data.

INSERT INTO employees_temp VALUES (employees_seq.NEXTVAL, 'Lynette', 'Smith');

-- If you need to store the same value somewhere else, you use CURRVAL

INSERT INTO employees_temp2 VALUES (employees_seq.CURRVAL, 'Morgan', 'Smith');

-- Because NEXTVAL values might be referenced by different users and

-- applications, and some NEXTVAL values might not be stored in the

-- database, there might be gaps in the sequence

-- The following uses the stored value of the CURRVAL in seq_value to specify

-- the record to delete because CURRVAL (or NEXTVAL) cannot used in a WHERE clause

-- This is invalid: WHERE employee_id = employees_seq.CURRVAL;

SELECT employees_seq.CURRVAL INTO seq_value FROM dual;

DELETE FROM employees_temp2 WHERE employee_id = seq_value;

-- The following udpates the employee_id with NEXTVAL for the specified record

UPDATE employees_temp SET employee_id = employees_seq.NEXTVAL

WHERE first_name = 'Lynette' AND last_name = 'Smith';

-- Display end value of CURRVAL

SELECT employees_seq.CURRVAL INTO seq_value FROM dual;

DBMS_OUTPUT.PUT_LINE ('Ending sequence value: ' || TO_CHAR(seq_value));

END;

6-4

Oracle Database PL/SQL User’s Guide and Reference

Overview of SQL Support in PL/SQL

LEVEL

You use

LEVEL

with the

SELECT CONNECT BY

statement to organize rows from a database table into a tree structure. You might use sequence numbers to give each row a unique identifier, and refer to those identifiers from other rows to set up parent-child relationships.

LEVEL

returns the level number of a node in a tree structure. The root is level 1, children of the root are level 2, grandchildren are level 3, and so on.

In the

START WITH

clause, you specify a condition that identifies the root of the tree.

You specify the direction in which the query traverses the tree (down from the root or up from the branches) with the

PRIOR

operator.

ROWID

returns the rowid (binary address) of a row in a database table. You can use variables of type

UROWID

to store rowids in a readable format.

When you select or fetch a physical rowid into a

UROWID

variable, you can use the function

ROWIDTOCHAR

, which converts the binary value to a character string. You can compare the

UROWID

variable to the

ROWID

pseudocolumn in the

WHERE

clause of an

UPDATE

DELETE

statement to identify the latest row fetched from a cursor. For an example, see

"Fetching Across Commits" on page 6-35.

ROWNUM

returns a number indicating the order in which a row was selected from a table. The first row selected has a

ROWNUM

of 1, the second row has a

ROWNUM

of 2, and so on. If a

SELECT

statement includes an

ORDER BY

clause,

ROWNUM s are assigned to the retrieved rows before the sort is done; use a subselect to get the first n sorted rows.

The value of

ROWNUM

increases only when a row is retrieved, so the only meaningful uses of

ROWNUM

in a

WHERE

clause are:

... WHERE ROWNUM < constant;

... WHERE ROWNUM <= constant;

You can use

ROWNUM

in an

UPDATE

statement to assign unique values to each row in a table, or in the

WHERE

clause of a

SELECT

statement to limit the number of rows

retrieved, as shown in Example 6–6

Example 6–6 Using ROWNUM

CREATE TABLE employees_temp AS SELECT * FROM employees;

DECLARE

CURSOR c1 IS SELECT employee_id, salary FROM employees_temp

WHERE salary > 2000 AND ROWNUM <= 10; -- 10 arbitrary rows

CURSOR c2 IS SELECT * FROM

(SELECT employee_id, salary FROM employees_temp

WHERE salary > 2000 ORDER BY salary DESC)

WHERE ROWNUM < 5; -- first 5 rows, in sorted order

BEGIN

-- Each row gets assigned a different number

UPDATE employees_temp SET employee_id = ROWNUM;

END;

Performing SQL Operations from PL/SQL

6-5

Managing Cursors in PL/SQL

SQL Operators

PL/SQL lets you use all the SQL comparison, set, and row operators in SQL statements. This section briefly describes some of these operators. For more information, see Oracle Database SQL Reference.

Comparison Operators

Typically, you use comparison operators in the

WHERE

clause of a data manipulation statement to form predicates, which compare one expression to another and yield

TRUE

FALSE

, or

NULL

. You can use the comparison operators in the following list to form predicates. You can combine predicates using the logical operators

AND

, and

NOT

Operator Description

ALL

EXISTS

Compares a value to each value in a list or returned by a subquery and yields

TRUE

if all of the individual comparisons yield

TRUE

ANY

SOME

Compares a value to each value in a list or returned by a subquery and yields

TRUE

if any of the individual comparisons yields

TRUE

BETWEEN

Tests whether a value lies in a specified range.

Returns

TRUE

if a subquery returns at least one row.

Tests for set membership.

IS NULL

Tests for nulls.

Tests whether a character string matches a specified pattern, which can include wildcards.

Set Operators

Set operators combine the results of two queries into one result.

INTERSECT

returns all distinct rows selected by both queries.

MINUS

returns all distinct rows selected by the first query but not by the second.

UNION

returns all distinct rows selected by either query.

UNION ALL

returns all rows selected by either query, including all duplicates.

Row Operators

Row operators return or reference particular rows.

ALL

retains duplicate rows in the result of a query or in an aggregate expression.

DISTINCT

eliminates duplicate rows from the result of a query or from an aggregate expression.

PRIOR

refers to the parent row of the current row returned by a tree-structured query.

Managing Cursors in PL/SQL

PL/SQL uses implicit and explicit cursors. PL/SQL declares a cursor implicitly for all

SQL data manipulation statements, including queries that return only one row. If you want precise control over query processing, you can declare an explicit cursor in the declarative part of any PL/SQL block, subprogram, or package. You must declare an explicit cursor for queries that return more than one row.

Implicit Cursors

Implicit cursors are managed automatically by PL/SQL so you are not required to write any code to handle these cursors. However, you can track information about the execution of an implicit cursor through its cursor attributes.

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Attributes of Implicit Cursors

Implicit cursor attributes return information about the execution of DML and DDL statements, such

INSERT

UPDATE

DELETE

SELECT INTO

COMMIT

, or

ROLLBACK statements. The cursor attributes are

%FOUND

%ISOPEN %NOTFOUND

, and

%ROWCOUNT

The values of the cursor attributes always refer to the most recently executed SQL statement. Before Oracle opens the

SQL

cursor, the implicit cursor attributes yield

NULL

The

SQL

cursor has another attribute,

%BULK_ROWCOUNT

, designed for use with the

FORALL

statement. For more information, see

"Counting Rows Affected by FORALL with the %BULK_ROWCOUNT Attribute" on page 11-12.

%FOUND Attribute: Has a DML Statement Changed Rows?

Until a SQL data manipulation statement is executed,

%FOUND

yields

NULL

. Thereafter,

%FOUND

yields

TRUE

if an

INSERT

UPDATE

, or

DELETE

statement affected one or more rows, or a

SELECT INTO

statement returned one or more rows. Otherwise,

%FOUND

yields

FALSE

. In Example 6–7

, you use

%FOUND

to insert a row if a delete succeeds.

Example 6–7 Using SQL%FOUND

CREATE TABLE dept_temp AS SELECT * FROM departments;

DECLARE

dept_no NUMBER(4) := 270;

BEGIN

DELETE FROM dept_temp WHERE department_id = dept_no;

IF SQL%FOUND THEN -- delete succeeded

INSERT INTO dept_temp VALUES (270, 'Personnel', 200, 1700);

END IF;

END;

%ISOPEN Attribute: Always FALSE for Implicit Cursors

Oracle closes the SQL cursor automatically after executing its associated SQL statement. As a result,

%ISOPEN

always yields

FALSE

%NOTFOUND Attribute: Has a DML Statement Failed to Change Rows?

%NOTFOUND

is the logical opposite of

%FOUND

%NOTFOUND

yields

TRUE

if an

INSERT

UPDATE

, or

DELETE

statement affected no rows, or a

SELECT INTO

statement returned no rows. Otherwise,

%NOTFOUND

yields

FALSE

%ROWCOUNT Attribute: How Many Rows Affected So Far?

%ROWCOUNT

yields the number of rows affected by an

INSERT

UPDATE

, or

DELETE statement, or returned by a

SELECT INTO

statement.

%ROWCOUNT

yields

if an

INSERT

UPDATE

, or

DELETE

statement affected no rows, or a

SELECT INTO

statement

returned no rows. In Example 6–8 ,

%ROWCOUNT

returns the number of rows that have been deleted.

Example 6–8 Using SQL%ROWCOUNT

CREATE TABLE employees_temp AS SELECT * FROM employees;

DECLARE

mgr_no NUMBER(6) := 122;

BEGIN

DELETE FROM employees_temp WHERE manager_id = mgr_no;

Performing SQL Operations from PL/SQL

6-7

Managing Cursors in PL/SQL

DBMS_OUTPUT.PUT_LINE('Number of employees deleted: ' || TO_CHAR(SQL%ROWCOUNT));

END;

If a

SELECT INTO

statement returns more than one row, PL/SQL raises the predefined exception

TOO_MANY_ROWS

and

%ROWCOUNT

yields

, not the actual number of rows that satisfy the query.

The value of the

SQL%ROWCOUNT

attribute refers to the most recently executed SQL statement from PL/SQL. To save an attribute value for later use, assign it to a local variable immediately.

The

SQL%ROWCOUNT

attribute is not related to the state of a transaction. When a rollback to a savepoint is performed, the value of

SQL%ROWCOUNT

is not restored to the old value before the savepoint was taken. Also, when an autonomous transaction is exited,

SQL%ROWCOUNT

is not restored to the original value in the parent transaction.

■

Guidelines for Using Attributes of Implicit Cursors

The following are considerations when using attributes of implicit cursors:

The values of the cursor attributes always refer to the most recently executed SQL statement, wherever that statement is. It might be in a different scope (for example, in a sub-block). To save an attribute value for later use, assign it to a local variable immediately. Doing other operations, such as procedure calls, might change the value of the variable before you can test it.

The

%NOTFOUND

attribute is not useful in combination with the

SELECT INTO statement:

–

If a

SELECT INTO

statement fails to return a row, PL/SQL raises the predefined exception

NO_DATA_FOUND

immediately, interrupting the flow of control before you can check

%NOTFOUND

–

SELECT INTO

statement that calls a SQL aggregate function always returns a value or a null. After such a statement, the

%NOTFOUND

attribute is always

FALSE

, so checking it is unnecessary.

Explicit Cursors

When you need precise control over query processing, you can explicitly declare a cursor in the declarative part of any PL/SQL block, subprogram, or package.

You use three commands to control a cursor:

OPEN

FETCH

, and

. First, you initialize the cursor with the

OPEN

statement, which identifies the result set. Then, you can execute

FETCH

repeatedly until all rows have been retrieved, or you can use the

BULK COLLECT

clause to fetch all rows at once. When the last row has been processed, you release the cursor with the

statement.

This technique requires more code than other techniques such as the implicit cursor

FOR loop. Its advantage is flexibility. You can:

■

Process several queries in parallel by declaring and opening multiple cursors.

■

Process multiple rows in a single loop iteration, skip rows, or split the processing into more than one loop.

Declaring a Cursor

You must declare a cursor before referencing it in other statements. You give the cursor a name and associate it with a specific query. You can optionally declare a return type

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Managing Cursors in PL/SQL for the cursor, such as table_name

%ROWTYPE

. You can optionally specify parameters that you use in the

WHERE

clause instead of referring to local variables. These parameters can have default values.

Example 6–9 shows how you can declare cursors.

Example 6–9 Declaring a Cursor

DECLARE

my_emp_id NUMBER(6); -- variable for employee_id

my_job_id VARCHAR2(10); -- variable for job_id

my_sal NUMBER(8,2); -- variable for salary

CURSOR c1 IS SELECT employee_id, job_id, salary FROM employees

WHERE salary > 2000;

my_dept departments%ROWTYPE; -- variable for departments row

CURSOR c2 RETURN departments%ROWTYPE IS

SELECT * FROM departments WHERE department_id = 110;

The cursor is not a PL/SQL variable: you cannot assign values to a cursor or use it in an expression. Cursors and variables follow the same scoping rules. Naming cursors after database tables is possible but not recommended.

A cursor can take parameters, which can appear in the associated query wherever constants can appear. The formal parameters of a cursor must be

parameters; they supply values in the query, but do not return any values from the query. You cannot impose the constraint

NOT NULL

on a cursor parameter.

As the following example shows, you can initialize cursor parameters to default values. You can pass different numbers of actual parameters to a cursor, accepting or overriding the default values as you please. Also, you can add new formal parameters without having to change existing references to the cursor.

DECLARE

CURSOR c1 (low NUMBER DEFAULT 0, high NUMBER DEFAULT 99) IS

SELECT * FROM departments WHERE department_id > low

AND department_id < high;

Cursor parameters can be referenced only within the query specified in the cursor declaration. The parameter values are used by the associated query when the cursor is opened.

Opening a Cursor

Opening the cursor executes the query and identifies the result set, which consists of all rows that meet the query search criteria. For cursors declared using the

FOR

UPDATE

clause, the

OPEN

statement also locks those rows. An example of the

OPEN statement follows:

DECLARE

CURSOR c1 IS SELECT employee_id, last_name, job_id, salary FROM employees

WHERE salary > 2000;

BEGIN

OPEN C1;

Rows in the result set are retrieved by the

FETCH

statement, not when the

OPEN statement is executed.

Fetching with a Cursor

Unless you use the

BULK COLLECT

clause, discussed in

"Fetching with a Cursor" on page 6-9, the

FETCH

statement retrieves the rows in the result set one at a time. Each

Performing SQL Operations from PL/SQL

6-9

Managing Cursors in PL/SQL fetch retrieves the current row and advances the cursor to the next row in the result set. You can store each column in a separate variable, or store the entire row in a record that has the appropriate fields, usually declared using

%ROWTYPE

For each column value returned by the query associated with the cursor, there must be a corresponding, type-compatible variable in the

INTO

list. Typically, you use the

FETCH

statement with a

LOOP

and

EXIT WHEN .. NOTFOUND

statements, as shown in

Example 6–10

. Note the use of built-in regular expression functions in the queries.

Example 6–10 Fetching With a Cursor

DECLARE

v_jobid employees.job_id%TYPE; -- variable for job_id

v_lastname employees.last_name%TYPE; -- variable for last_name

CURSOR c1 IS SELECT last_name, job_id FROM employees

WHERE REGEXP_LIKE (job_id, 'S[HT]_CLERK');

v_employees employees%ROWTYPE; -- record variable for row

CURSOR c2 is SELECT * FROM employees

WHERE REGEXP_LIKE (job_id, '[ACADFIMKSA]_M[ANGR]');

BEGIN

OPEN c1; -- open the cursor before fetching

LOOP

FETCH c1 INTO v_lastname, v_jobid; -- fetches 2 columns into variables

EXIT WHEN c1%NOTFOUND;

DBMS_OUTPUT.PUT_LINE( RPAD(v_lastname, 25, ' ') || v_jobid );

END LOOP;

CLOSE c1;

DBMS_OUTPUT.PUT_LINE( '-------------------------------------' );

OPEN c2;

LOOP

FETCH c2 INTO v_employees; -- fetches entire row into the v_employees record

EXIT WHEN c2%NOTFOUND;

DBMS_OUTPUT.PUT_LINE( RPAD(v_employees.last_name, 25, ' ') ||

v_employees.job_id );

END LOOP;

CLOSE c2;

END;

The query can reference PL/SQL variables within its scope. Any variables in the query are evaluated only when the cursor is opened. In

Example 6–11 , each retrieved salary

is multiplied by

, even though factor

is incremented after every fetch.

Example 6–11 Referencing PL/SQL Variables Within Its Scope

DECLARE

my_sal employees.salary%TYPE;

my_job employees.job_id%TYPE;

factor INTEGER := 2;

CURSOR c1 IS

SELECT factor*salary FROM employees WHERE job_id = my_job;

BEGIN

OPEN c1; -- factor initially equals 2

LOOP

FETCH c1 INTO my_sal;

EXIT WHEN c1%NOTFOUND;

factor := factor + 1; -- does not affect FETCH

END LOOP;

CLOSe c1;

END;

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Managing Cursors in PL/SQL

To change the result set or the values of variables in the query, you must close and reopen the cursor with the input variables set to their new values. However, you can use a different

INTO

list on separate fetches with the same cursor. Each fetch retrieves another row and assigns values to the target variables, as shown in

Example 6–12

Example 6–12 Fetching the Same Cursor Into Different Variables

DECLARE

CURSOR c1 IS SELECT last_name FROM employees ORDER BY last_name;

name1 employees.last_name%TYPE;

name2 employees.last_name%TYPE;

name3 employees.last_name%TYPE;

BEGIN

OPEN c1;

FETCH c1 INTO name1; -- this fetches first row

FETCH c1 INTO name2; -- this fetches second row

FETCH c1 INTO name3; -- this fetches third row

CLOSE c1;

END;

If you fetch past the last row in the result set, the values of the target variables are undefined. Eventually, the

FETCH

statement fails to return a row. When that happens, no exception is raised. To detect the failure, use the cursor attribute

%FOUND

%NOTFOUND

. For more information, see

"Using Cursor Expressions" on page 6-28.

Fetching Bulk Data with a Cursor

The

BULK COLLECT

clause lets you fetch all rows from the result set at once. See

"Retrieving Query Results into Collections with the BULK COLLECT Clause" on page 11-15. In

Example 6–13

, you bulk-fetch from a cursor into two collections.

Example 6–13 Fetching Bulk Data With a Cursor

DECLARE

TYPE IdsTab IS TABLE OF employees.employee_id%TYPE;

TYPE NameTab IS TABLE OF employees.last_name%TYPE;

ids IdsTab;

names NameTab;

CURSOR c1 IS

SELECT employee_id, last_name FROM employees WHERE job_id = 'ST_CLERK';

BEGIN

OPEN c1;

FETCH c1 BULK COLLECT INTO ids, names;

CLOsE c1;

-- Here is where you process the elements in the collections

FOR i IN ids.FIRST .. ids.LAST

LOOP

IF ids(i) > 140 THEN

DBMS_OUTPUT.PUT_LINE( ids(i) );

END IF;

END LOOP;

FOR i IN names.FIRST .. names.LAST

LOOP

IF names(i) LIKE '%Ma%' THEN

DBMS_OUTPUT.PUT_LINE( names(i) );

END IF;

END LOOP;

Performing SQL Operations from PL/SQL

6-11

Managing Cursors in PL/SQL

END;

Closing a Cursor

The

statement disables the cursor, and the result set becomes undefined. Once a cursor is closed, you can reopen it, which runs the query again with the latest values of any cursor parameters and variables referenced in the

WHERE

clause. Any other operation on a closed cursor raises the predefined exception

INVALID_CURSOR

Attributes of Explicit Cursors

Every explicit cursor and cursor variable has four attributes:

%FOUND

%ISOPEN

%NOTFOUND

, and

%ROWCOUNT

. When appended to the cursor or cursor variable name, these attributes return useful information about the execution of a SQL statement. You can use cursor attributes in procedural statements but not in SQL statements.

Explicit cursor attributes return information about the execution of a multi-row query.

When an explicit cursor or a cursor variable is opened, the rows that satisfy the associated query are identified and form the result set. Rows are fetched from the result set.

%FOUND Attribute: Has a Row Been Fetched?

After a cursor or cursor variable is opened but before the first fetch,

%FOUND

returns

NULL

. After any fetches, it returns

TRUE

if the last fetch returned a row, or

FALSE

if the last fetch did not return a row.

Example 6–14 uses

%FOUND

to select an action.

Example 6–14 Using %FOUND

DECLARE

CURSOR c1 IS SELECT last_name, salary FROM employees WHERE ROWNUM < 11;

my_ename employees.last_name%TYPE;

my_salary employees.salary%TYPE;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO my_ename, my_salary;

IF c1%FOUND THEN -- fetch succeeded

DBMS_OUTPUT.PUT_LINE('Name = ' || my_ename || ', salary = ' || my_salary);

ELSE -- fetch failed, so exit loop

EXIT;

END IF;

END LOOP;

END;

If a cursor or cursor variable is not open, referencing it with

%FOUND

raises the predefined exception

INVALID_CURSOR

%ISOPEN Attribute: Is the Cursor Open?

%ISOPEN

returns

TRUE

if its cursor or cursor variable is open; otherwise,

%ISOPEN returns

FALSE

Example 6–15 uses

%ISOPEN

to select an action.

Example 6–15 Using %ISOPEN

DECLARE

CURSOR c1 IS SELECT last_name, salary FROM employees WHERE ROWNUM < 11;

the_name employees.last_name%TYPE;

the_salary employees.salary%TYPE;

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Managing Cursors in PL/SQL

BEGIN

IF c1%ISOPEN = FALSE THEN -- cursor was not already open

OPEN c1;

END IF;

FETCH c1 INTO the_name, the_salary;

CLOSE c1;

END;

%NOTFOUND Attribute: Has a Fetch Failed?

%NOTFOUND

is the logical opposite of

%FOUND

%NOTFOUND

yields

FALSE

if the last fetch returned a row, or

TRUE

if the last fetch failed to return a row. In Example 6–16 ,

you use

%NOTFOUND

to exit a loop when

FETCH

fails to return a row.

Example 6–16 Using %NOTFOUND

DECLARE

CURSOR c1 IS SELECT last_name, salary FROM employees WHERE ROWNUM < 11;

my_ename employees.last_name%TYPE;

my_salary employees.salary%TYPE;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO my_ename, my_salary;

IF c1%NOTFOUND THEN -- fetch failed, so exit loop

-- Another form of this test is "EXIT WHEN c1%NOTFOUND OR c1%NOTFOUND IS NULL;"

EXIT;

ELSE -- fetch succeeded

DBMS_OUTPUT.PUT_LINE('Name = ' || my_ename || ', salary = ' || my_salary);

END IF;

END LOOP;

END;

Before the first fetch,

%NOTFOUND

returns

NULL

. If

FETCH

never executes successfully, the loop is never exited, because the

EXIT WHEN

statement executes only if its

WHEN condition is true. To be safe, you might want to use the following

EXIT

statement instead:

EXIT WHEN c1%NOTFOUND OR c1%NOTFOUND IS NULL;

If a cursor or cursor variable is not open, referencing it with

%NOTFOUND

raises an

INVALID_CURSOR

exception.

%ROWCOUNT Attribute: How Many Rows Fetched So Far?

When its cursor or cursor variable is opened,

%ROWCOUNT

is zeroed. Before the first fetch,

%ROWCOUNT

yields

. Thereafter, it yields the number of rows fetched so far. The

number is incremented if the last fetch returned a row. Example 6–17 uses

%ROWCOUNT to test if more than ten rows have been fetched.

Example 6–17 Using %ROWCOUNT

DECLARE

CURSOR c1 IS SELECT last_name FROM employees WHERE ROWNUM < 11;

name employees.last_name%TYPE;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO name;

Performing SQL Operations from PL/SQL

6-13

Querying Data with PL/SQL

EXIT WHEN c1%NOTFOUND OR c1%NOTFOUND IS NULL;

DBMS_OUTPUT.PUT_LINE(c1%ROWCOUNT || '. ' || name);

IF c1%ROWCOUNT = 5 THEN

DBMS_OUTPUT.PUT_LINE('--- Fetched 5th record ---');

END IF;

END LOOP;

CLOSE c1;

END;

If a cursor or cursor variable is not open, referencing it with

%ROWCOUNT

raises

INVALID_CURSOR

Table 6–1 shows what each cursor attribute returns before and after you execute an

OPEN

FETCH

, or

statement.

Table 6–1 Cursor Attribute Values

OPEN

First FETCH

Last FETCH

%FOUND %ISOPEN %NOTFOUND %ROWCOUNT

before exception

FALSE after before

NULL

NULL after

TRUE

Next FETCH(es) before

TRUE

TRUE after

TRUE before

TRUE after

FALSE before

FALSE after

TRUE

TRUE exception

FALSE exception

NULL

FALSE

TRUE

TRUE exception exception

1 data dependent data dependent data dependent data dependent exception

The following applies to the information in

Table 6–1 :

■

Referencing

%FOUND

%NOTFOUND

, or

%ROWCOUNT

before a cursor is opened or after it is closed raises

INVALID_CURSOR

■

After the first

FETCH

, if the result set was empty,

%FOUND

yields

FALSE

%NOTFOUND

yields

TRUE

, and

%ROWCOUNT

yields 0.

Querying Data with PL/SQL

PL/SQL lets you perform queries (

SELECT

statements in SQL) and access individual fields or entire rows from the result set. In traditional database programming, you process query results using an internal data structure called a cursor. In most situations, PL/SQL can manage the cursor for you, so that code to process query results is straightforward and compact. This section discusses how to process both simple queries where PL/SQL manages everything, and complex queries where you interact with the cursor.

Selecting At Most One Row: SELECT INTO Statement

If you expect a query to only return one row, you can write a regular SQL

SELECT statement with an additional

INTO

clause specifying the PL/SQL variable to hold the result.

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If the query might return more than one row, but you do not care about values after the first, you can restrict any result set to a single row by comparing the

ROWNUM

value.

If the query might return no rows at all, use an exception handler to specify any actions to take when no data is found.

If you just want to check whether a condition exists in your data, you might be able to code the query with the

COUNT(*)

operator, which always returns a number and never raises the

NO_DATA_FOUND

exception.

Selecting Multiple Rows: BULK COLLECT Clause

If you need to bring a large quantity of data into local PL/SQL variables, rather than looping through a result set one row at a time, you can use the

BULK COLLECT

clause.

When you query only certain columns, you can store all the results for each column in a separate collection variable. When you query all the columns of a table, you can store the entire result set in a collection of records, which makes it convenient to loop

through the results and refer to different columns. See Example 6–13, "Fetching Bulk

Data With a Cursor" on page 6-11.

This technique can be very fast, but also very memory-intensive. If you use it often, you might be able to improve your code by doing more of the work in SQL:

■

If you only need to loop once through the result set, use a

FOR

loop as described in the following sections. This technique avoids the memory overhead of storing a copy of the result set.

■

If you are looping through the result set to scan for certain values or filter the results into a smaller set, do this scanning or filtering in the original query instead.

You can add more

WHERE

clauses in simple cases, or use set operators such as

INTERSECT

and

MINUS

if you are comparing two or more sets of results.

If you are looping through the result set and running another query or a DML statement for each result row, you can probably find a more efficient technique.

For queries, look at including subqueries or

EXISTS

NOT EXISTS

clauses in the original query. For DML statements, look at the

FORALL

statement, which is much faster than coding these statements inside a regular loop.

Looping Through Multiple Rows: Cursor FOR Loop

Perhaps the most common case of a query is one where you issue the

SELECT statement, then immediately loop once through the rows of the result set. PL/SQL lets you use a simple

FOR

loop for this kind of query:

The iterator variable for the

FOR

loop does not need to be declared in advance. It is a

%ROWTYPE

record whose field names match the column names from the query, and that exists only during the loop. When you use expressions rather than explicit column names, use column aliases so that you can refer to the corresponding values inside the loop.

Performing Complicated Query Processing: Explicit Cursors

For full control over query processing, you can use explicit cursors in combination with the

OPEN

FETCH

, and

statements.

You might want to specify a query in one place but retrieve the rows somewhere else, even in another subprogram. Or you might want to choose very different query parameters, such as

ORDER BY

GROUP BY

clauses, depending on the situation. Or you might want to process some rows differently than others, and so need more than a simple loop.

Performing SQL Operations from PL/SQL

6-15

Querying Data with PL/SQL

Because explicit cursors are so flexible, you can choose from different notations depending on your needs. The following sections describe all the query-processing features that explicit cursors provide.

Querying Data with PL/SQL: Implicit Cursor FOR Loop

With PL/SQL, it is very simple to issue a query, retrieve each row of the result into a

%ROWTYPE

record, and process each row in a loop:

■

You include the text of the query directly in the

FOR

loop.

PL/SQL creates a record variable with fields corresponding to the columns of the result set.

■

You refer to the fields of this record variable inside the loop. You can perform tests and calculations, display output, or store the results somewhere else.

Here is an example that you can run in SQL*Plus. It does a query to get the name and job Id of employees with manager Ids greater than 120.

BEGIN

FOR item IN

( SELECT last_name, job_id FROM employees WHERE job_id LIKE '%CLERK%'

AND manager_id > 120 )

LOOP

DBMS_OUTPUT.PUT_LINE('Name = ' || item.last_name || ', Job = ' ||

item.job_id);

END LOOP;

END;

Before each iteration of the

FOR

loop, PL/SQL fetches into the implicitly declared record. The sequence of statements inside the loop is executed once for each row that satisfies the query. When you leave the loop, the cursor is closed automatically. The cursor is closed even if you use an

EXIT

GOTO

statement to leave the loop before all rows are fetched, or an exception is raised inside the loop. See

"LOOP Statements" on page 13-72.

Querying Data with PL/SQL: Explicit Cursor FOR Loops

If you need to reference the same query from different parts of the same procedure, you can declare a cursor that specifies the query, and process the results using a FOR loop.

DECLARE

CURSOR c1 IS SELECT last_name, job_id FROM employees

WHERE job_id LIKE '%CLERK%' AND manager_id > 120;

BEGIN

FOR item IN c1

LOOP

DBMS_OUTPUT.PUT_LINE('Name = ' || item.last_name || ', Job = ' ||

item.job_id);

END LOOP;

END;

Defining Aliases for Expression Values in a Cursor FOR Loop

In a cursor FOR loop, PL/SQL creates a

%ROWTYPE

record with fields corresponding to columns in the result set. The fields have the same names as corresponding columns in the

SELECT

list.

The select list might contain an expression, such as a column plus a constant, or two columns concatenated together. If so, use a column alias to give unique names to the appropriate columns.

Example 6–18 ,

full_name

and dream_salary

are aliases for expressions in the query:

Example 6–18 Using an Alias For Expressions in a Query

BEGIN

FOR item IN

( SELECT first_name || ' ' || last_name AS full_name,

salary * 10 AS dream_salary FROM employees WHERE ROWNUM <= 5 )

LOOP

DBMS_OUTPUT.PUT_LINE(item.full_name || ' dreams of making ' ||

item.dream_salary);

END LOOP;

END;

Using Subqueries

A subquery is a query (usually enclosed by parentheses) that appears within another

SQL data manipulation statement. The statement acts upon the single value or set of values returned by the subquery. For example:

■

You can use a subquery to find the

MAX()

MIN()

, or

AVG()

value for a column, and use that single value in a comparison in a

WHERE

clause.

You can use a subquery to find a set of values, and use this values in an

NOT

comparison in a

WHERE

clause. This technique can avoid joins.

You can filter a set of values with a subquery, and apply other operations like

ORDER BY

and

GROUP BY

in the outer query.

You can use a subquery in place of a table name, in the

FROM

clause of a query.

This technique lets you join a table with a small set of rows from another table, instead of joining the entire tables.

■

You can create a table or insert into a table, using a set of rows defined by a subquery.

Example 6–19 is illustrates two subqueries used in cursor declarations.

Example 6–19 Using a Subquery in a Cursor

DECLARE

CURSOR c1 IS

-- main query returns only rows where the salary is greater than the average

SELECT employee_id, last_name FROM employees

WHERE salary > (SELECT AVG(salary) FROM employees);

CURSOR c2 IS

-- subquery returns all the rows in descending order of salary

-- main query returns just the top 10 highest-paid employees

SELECT * FROM

(SELECT last_name, salary FROM employees ORDER BY salary DESC, last_name)

Performing SQL Operations from PL/SQL

6-17

Using Subqueries

WHERE ROWNUM < 11;

BEGIN

FOR person IN c1

LOOP

DBMS_OUTPUT.PUT_LINE('Above-average salary: ' || person.last_name);

END LOOP;

FOR person IN c2

LOOP

DBMS_OUTPUT.PUT_LINE('Highest paid: ' || person.last_name ||

' $' || person.salary);

END LOOP;

-- subquery identifies a set of rows to use with CREATE TABLE or INSERT

END;

Using a subquery in the

FROM

clause, the query in

Example 6–20

returns the number and name of each department with five or more employees.

Example 6–20 Using a Subquery in a FROM Clause

DECLARE

CURSOR c1 IS

SELECT t1.department_id, department_name, staff

FROM departments t1,

( SELECT department_id, COUNT(*) as staff

FROM employees GROUP BY department_id) t2

WHERE

t1.department_id = t2.department_id

AND staff >= 5;

BEGIN

FOR dept IN c1

LOOP

DBMS_OUTPUT.PUT_LINE('Department = ' || dept.department_name ||

', staff = ' || dept.staff);

END LOOP;

END;

Using Correlated Subqueries

While a subquery is evaluated only once for each table, a correlated subquery is

evaluated once for each row. Example 6–21 returns the name and salary of each

employee whose salary exceeds the departmental average. For each row in the table, the correlated subquery computes the average salary for the corresponding department.

Example 6–21 Using a Correlated Subquery

DECLARE

-- For each department, find the average salary. Then find all the employees in

-- that department making more than that average salary.

CURSOR c1 IS

SELECT department_id, last_name, salary FROM employees t

WHERE salary >

( SELECT AVG(salary) FROM employees WHERE t.department_id = department_id )

ORDER BY department_id;

BEGIN

FOR person IN c1

LOOP

DBMS_OUTPUT.PUT_LINE('Making above-average salary = ' || person.last_name);

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Using Subqueries

END LOOP;

END;

Writing Maintainable PL/SQL Queries

Instead of referring to local variables, you can declare a cursor that accepts parameters, and pass values for those parameters when you open the cursor. If the query is usually issued with certain values, you can make those values the defaults. You can use either positional notation or named notation to pass the parameter values.

Example 6–22 displays the wages paid to employees earning over a specified wage in

a specified department.

Example 6–22 Passing Parameters to a Cursor FOR Loop

DECLARE

CURSOR c1 (job VARCHAR2, max_wage NUMBER) IS

SELECT * FROM employees WHERE job_id = job AND salary > max_wage;

BEGIN

FOR person IN c1('CLERK', 3000)

LOOP

-- process data record

DBMS_OUTPUT.PUT_LINE('Name = ' || person.last_name || ', salary = ' ||

person.salary || ', Job Id = ' || person.job_id );

END LOOP;

END;

Example 6–23 , several ways are shown to open a cursor.

Example 6–23 Passing Parameters to Explicit Cursors

DECLARE

emp_job employees.job_id%TYPE := 'ST_CLERK';

emp_salary employees.salary%TYPE := 3000;

my_record employees%ROWTYPE;

CURSOR c1 (job VARCHAR2, max_wage NUMBER) IS

SELECT * FROM employees WHERE job_id = job and salary > max_wage;

BEGIN

-- Any of the following statements opens the cursor:

-- OPEN c1('ST_CLERK', 3000); OPEN c1('ST_CLERK', emp_salary);

-- OPEN c1(emp_job, 3000); OPEN c1(emp_job, emp_salary);

OPEN c1(emp_job, emp_salary);

LOOP

FETCH c1 INTO my_record;

EXIT WHEN c1%NOTFOUND;

-- process data record

DBMS_OUTPUT.PUT_LINE('Name = ' || my_record.last_name || ', salary = ' ||

my_record.salary || ', Job Id = ' || my_record.job_id );

END LOOP;

END;

To avoid confusion, use different names for cursor parameters and the PL/SQL variables that you pass into those parameters.

Formal parameters declared with a default value do not need a corresponding actual parameter. If you omit them, they assume their default values when the

OPEN statement is executed.

Performing SQL Operations from PL/SQL

6-19

Using Cursor Variables (REF CURSORs)

Like a cursor, a cursor variable points to the current row in the result set of a multi-row query. A cursor variable is more flexible because it is not tied to a specific query. You can open a cursor variable for any query that returns the right set of columns.

You pass a cursor variable as a parameter to local and stored subprograms. Opening the cursor variable in one subprogram, and processing it in a different subprogram, helps to centralize data retrieval. This technique is also useful for multi-language applications, where a PL/SQL subprogram might return a result set to a subprogram written in a different language, such as Java or Visual Basic.

Cursor variables are available to every PL/SQL client. For example, you can declare a cursor variable in a PL/SQL host environment such as an OCI or Pro*C program, then pass it as an input host variable (bind variable) to PL/SQL. Application development tools such as Oracle Forms, which have a PL/SQL engine, can use cursor variables entirely on the client side. Or, you can pass cursor variables back and forth between a client and the database server through remote procedure calls.

What Are Cursor Variables (REF CURSORs)?

Cursor variables are like pointers to result sets. You use them when you want to perform a query in one subprogram, and process the results in a different subprogram

(possibly one written in a different language). A cursor variable has datatype

REF

CURSOR

, and you might see them referred to informally as

REF CURSOR s.

Unlike an explicit cursor, which always refers to the same query work area, a cursor variable can refer to different work areas. You cannot use a cursor variable where a cursor is expected, or vice versa.

Why Use Cursor Variables?

You use cursor variables to pass query result sets between PL/SQL stored subprograms and various clients. PL/SQL and its clients share a pointer to the query work area in which the result set is stored. For example, an OCI client, Oracle Forms application, and Oracle database server can all refer to the same work area.

A query work area remains accessible as long as any cursor variable points to it, as you pass the value of a cursor variable from one scope to another. For example, if you pass a host cursor variable to a PL/SQL block embedded in a Pro*C program, the work area to which the cursor variable points remains accessible after the block completes.

If you have a PL/SQL engine on the client side, calls from client to server impose no restrictions. For example, you can declare a cursor variable on the client side, open and fetch from it on the server side, then continue to fetch from it back on the client side.

You can also reduce network traffic by having a PL/SQL block open or close several host cursor variables in a single round trip.

Declaring REF CURSOR Types and Cursor Variables

To create cursor variables, you define a

REF CURSOR

type, then declare cursor variables of that type. You can define

REF CURSOR

types in any PL/SQL block, subprogram, or package. In the following example, you declare a

REF CURSOR

type that represents a result set from the

DEPARTMENTS

table:

DECLARE

TYPE DeptCurTyp IS REF CURSOR RETURN departments%ROWTYPE;

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Using Cursor Variables (REF CURSORs)

REF CURSOR

types can be strong (with a return type) or weak (with no return type).

Strong

REF CURSOR

types are less error prone because the PL/SQL compiler lets you associate a strongly typed cursor variable only with queries that return the right set of columns. Weak

REF CURSOR

types are more flexible because the compiler lets you associate a weakly typed cursor variable with any query. Because there is no type checking with a weak

REF CURSOR

, all such types are interchangeable. Instead of creating a new type, you can use the predefined type

SYS_REFCURSOR

Once you define a

REF CURSOR

type, you can declare cursor variables of that type in any PL/SQL block or subprogram.

DECLARE

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE; -- strong

TYPE genericcurtyp IS REF CURSOR; -- weak

cursor1 empcurtyp;

cursor2 genericcurtyp;

my_cursor SYS_REFCURSOR; -- didn't need to declare a new type

TYPE deptcurtyp IS REF CURSOR RETURN departments%ROWTYPE;

dept_cv deptcurtyp; -- declare cursor variable

To avoid declaring the same

REF CURSOR

type in each subprogram that uses it, you can put the

REF CURSOR

declaration in a package spec. You can declare cursor variables of that type in the corresponding package body, or within your own procedure or function.

In the

RETURN

clause of a

REF CURSOR

type definition, you can use

%ROWTYPE

to refer

to a strongly typed cursor variable, as shown in Example 6–24 .

Example 6–24 Cursor Variable Returning a %ROWTYPE Variable

DECLARE

TYPE TmpCurTyp IS REF CURSOR RETURN employees%ROWTYPE;

tmp_cv TmpCurTyp; -- declare cursor variable

TYPE EmpCurTyp IS REF CURSOR RETURN tmp_cv%ROWTYPE;

emp_cv EmpCurTyp; -- declare cursor variable

You can also use

%ROWTYPE

to provide the datatype of a record variable, as shown in

Example 6–25 .

Example 6–25 Using the %ROWTYPE Attribute to Provide the Datatype

DECLARE

dept_rec departments%ROWTYPE; -- declare record variable

TYPE DeptCurTyp IS REF CURSOR RETURN dept_rec%TYPE;

dept_cv DeptCurTyp; -- declare cursor variable

Example 6–26 specifies a user-defined

RECORD

type in the

RETURN

clause:

Example 6–26 Cursor Variable Returning a Record Type

DECLARE

TYPE EmpRecTyp IS RECORD (

employee_id NUMBER,

last_name VARCHAR2(25),

salary NUMBER(8,2));

TYPE EmpCurTyp IS REF CURSOR RETURN EmpRecTyp;

emp_cv EmpCurTyp; -- declare cursor variable

Performing SQL Operations from PL/SQL

6-21

Using Cursor Variables (REF CURSORs)

Passing Cursor Variables As Parameters

You can declare cursor variables as the formal parameters of functions and procedures.

Example 6–27 defines a

REF CURSOR

type, then declares a cursor variable of that type as a formal parameter.

Example 6–27 Passing a REF CURSOR as a Parameter

DECLARE

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;

emp empcurtyp;

-- after result set is built, process all the rows inside a single procedure

-- rather than calling a procedure for each row

PROCEDURE process_emp_cv (emp_cv IN empcurtyp) IS

person employees%ROWTYPE;

BEGIN

DBMS_OUTPUT.PUT_LINE('-----');

DBMS_OUTPUT.PUT_LINE('Here are the names from the result set:');

LOOP

FETCH emp_cv INTO person;

EXIT WHEN emp_cv%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('Name = ' || person.first_name ||

' ' || person.last_name);

END LOOP;

END;

BEGIN

-- First find 10 arbitrary employees.

OPEN emp FOR SELECT * FROM employees WHERE ROWNUM < 11;

process_emp_cv(emp);

CLOSE emp;

-- find employees matching a condition.

OPEN emp FOR SELECT * FROM employees WHERE last_name LIKE 'R%';

process_emp_cv(emp);

CLOSE emp;

END;

Like all pointers, cursor variables increase the possibility of parameter aliasing. See

"Overloading Subprogram Names" on page 8-10.

Controlling Cursor Variables: OPEN-FOR, FETCH, and CLOSE

You use three statements to control a cursor variable:

OPEN-FOR

FETCH

, and

First, you

OPEN

a cursor variable

FOR

a multi-row query. Then, you

FETCH

rows from the result set. When all the rows are processed, you

the cursor variable.

Opening a Cursor Variable

The

OPEN-FOR

statement associates a cursor variable with a multi-row query, executes the query, and identifies the result set. The cursor variable can be declared directly in

PL/SQL, or in a PL/SQL host environment such as an OCI program. For the syntax of the

OPEN-FOR

statement, see "OPEN-FOR Statement" on page 13-82.

The

SELECT

statement for the query can be coded directly in the statement, or can be a string variable or string literal. When you use a string as the query, it can include placeholders for bind variables, and you specify the corresponding values with a

USING clause.

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Using Cursor Variables (REF CURSORs)

This section discusses the static SQL case, in which select_statement

is used. For the dynamic SQL case, in which dynamic_string

is used, see "OPEN-FOR

Statement" on page 13-82.

Unlike cursors, cursor variables take no parameters. Instead, you can pass whole queries (not just parameters) to a cursor variable. The query can reference host variables and PL/SQL variables, parameters, and functions.

Example 6–28 opens a cursor variable. Notice that you can apply cursor attributes

(

%FOUND

%NOTFOUND

%ISOPEN

, and

%ROWCOUNT

) to a cursor variable.

Example 6–28 Checking If a Cursor Variable is Open

DECLARE

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;

emp_cv empcurtyp;

BEGIN

IF NOT emp_cv%ISOPEN THEN -- open cursor variable

OPEN emp_cv FOR SELECT * FROM employees;

END IF;

CLOSE emp_cv;

END;

Other

OPEN-FOR

statements can open the same cursor variable for different queries.

You need not close a cursor variable before reopening it. Note that consecutive

OPEN s of a static cursor raise the predefined exception

CURSOR_ALREADY_OPEN

. When you reopen a cursor variable for a different query, the previous query is lost.

Typically, you open a cursor variable by passing it to a stored procedure that declares an

IN OUT

parameter that is a cursor variable. In Example 6–29 the procedure opens a

cursor variable.

Example 6–29 Stored Procedure to Open a Ref Cursor

CREATE PACKAGE emp_data AS

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;

PROCEDURE open_emp_cv (emp_cv IN OUT empcurtyp);

END emp_data;

CREATE PACKAGE BODY emp_data AS

PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp) IS

BEGIN

OPEN emp_cv FOR SELECT * FROM employees;

END open_emp_cv;

END emp_data;

You can also use a standalone stored procedure to open the cursor variable. Define the

REF CURSOR

type in a package, then reference that type in the parameter declaration for the stored procedure.

To centralize data retrieval, you can group type-compatible queries in a stored procedure. In

Example 6–30 , the packaged procedure declares a selector as one of its

formal parameters. When called, the procedure opens the cursor variable emp_cv

for the chosen query.

Example 6–30 Stored Procedure to Open Ref Cursors with Different Queries

CREATE PACKAGE emp_data AS

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;

Performing SQL Operations from PL/SQL

6-23

Using Cursor Variables (REF CURSORs)

PROCEDURE open_emp_cv (emp_cv IN OUT empcurtyp, choice INT);

END emp_data;

CREATE PACKAGE BODY emp_data AS

PROCEDURE open_emp_cv (emp_cv IN OUT empcurtyp, choice INT) IS

BEGIN

IF choice = 1 THEN

OPEN emp_cv FOR SELECT * FROM employees WHERE commission_pct IS NOT NULL;

ELSIF choice = 2 THEN

OPEN emp_cv FOR SELECT * FROM employees WHERE salary > 2500;

ELSIF choice = 3 THEN

OPEN emp_cv FOR SELECT * FROM employees WHERE department_id = 100;

END IF;

END;

END emp_data;

For more flexibility, a stored procedure can execute queries with different return types,

shown in Example 6–31 .

Example 6–31 Cursor Variable with Different Return Types

CREATE PACKAGE admin_data AS

TYPE gencurtyp IS REF CURSOR;

PROCEDURE open_cv (generic_cv IN OUT gencurtyp, choice INT);

END admin_data;

CREATE PACKAGE BODY admin_data AS

PROCEDURE open_cv (generic_cv IN OUT gencurtyp, choice INT) IS

BEGIN

IF choice = 1 THEN

OPEN generic_cv FOR SELECT * FROM employees;

ELSIF choice = 2 THEN

OPEN generic_cv FOR SELECT * FROM departments;

ELSIF choice = 3 THEN

OPEN generic_cv FOR SELECT * FROM jobs;

END IF;

END;

END admin_data;

Using a Cursor Variable as a Host Variable

You can declare a cursor variable in a PL/SQL host environment such as an OCI or

Pro*C program. To use the cursor variable, you must pass it as a host variable to

PL/SQL. In the following Pro*C example, you pass a host cursor variable and selector to a PL/SQL block, which opens the cursor variable for the chosen query.

EXEC SQL BEGIN DECLARE SECTION;

...

/* Declare host cursor variable. */

SQL_CURSOR generic_cv; int choice;

EXEC SQL END DECLARE SECTION;

...

/* Initialize host cursor variable. */

EXEC SQL ALLOCATE :generic_cv;

...

/* Pass host cursor variable and selector to PL/SQL block. */

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Using Cursor Variables (REF CURSORs)

EXEC SQL EXECUTE

BEGIN

IF :choice = 1 THEN

OPEN :generic_cv FOR SELECT * FROM employees;

ELSIF :choice = 2 THEN

OPEN :generic_cv FOR SELECT * FROM departments;

ELSIF :choice = 3 THEN

OPEN :generic_cv FOR SELECT * FROM jobs;

END IF;

END;

END-EXEC;

Host cursor variables are compatible with any query return type. They behave just like weakly typed PL/SQL cursor variables.

Fetching from a Cursor Variable

The

FETCH

statement retrieves rows from the result set of a multi-row query. It works

the same with cursor variables as with explicit cursors. Example 6–32 fetches rows one

at a time from a cursor variable into a record.

Example 6–32 Fetching from a Cursor Variable into a Record

DECLARE

TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;

emp_cv empcurtyp;

emp_rec employees%ROWTYPE;

BEGIN

OPEN emp_cv FOR SELECT * FROM employees WHERE employee_id < 120;

LOOP

FETCH emp_cv INTO emp_rec; -- fetch from cursor variable

EXIT WHEN emp_cv%NOTFOUND; -- exit when last row is fetched

-- process data record

DBMS_OUTPUT.PUT_LINE('Name = ' || emp_rec.first_name || ' ' ||

emp_rec.last_name);

END LOOP;

CLOSE emp_cv;

END;

Using the

BULK COLLECT

clause, you can bulk fetch rows from a cursor variable into

one or more collections as shown in Example 6–33

Example 6–33 Fetching from a Cursor Variable into Collections

DECLARE

TYPE empcurtyp IS REF CURSOR;

TYPE namelist IS TABLE OF employees.last_name%TYPE;

TYPE sallist IS TABLE OF employees.salary%TYPE;

emp_cv empcurtyp;

names namelist;

sals sallist;

BEGIN

OPEN emp_cv FOR SELECT last_name, salary FROM employees

WHERE job_id = 'SA_REP';

FETCH emp_cv BULK COLLECT INTO names, sals;

CLOSE emp_cv;

-- loop through the names and sals collections

FOR i IN names.FIRST .. names.LAST

Performing SQL Operations from PL/SQL

6-25

Using Cursor Variables (REF CURSORs)

LOOP

DBMS_OUTPUT.PUT_LINE('Name = ' || names(i) || ', salary = ' || sals(i));

END LOOP;

END;

Any variables in the associated query are evaluated only when the cursor variable is opened. To change the result set or the values of variables in the query, reopen the cursor variable with the variables set to new values. You can use a different

INTO clause on separate fetches with the same cursor variable. Each fetch retrieves another row from the same result set.

PL/SQL makes sure the return type of the cursor variable is compatible with the

INTO clause of the

FETCH

statement. If there is a mismatch, an error occurs at compile time if the cursor variable is strongly typed, or at run time if it is weakly typed. At run time,

PL/SQL raises the predefined exception

ROWTYPE_MISMATCH

before the first fetch. If you trap the error and execute the

FETCH

statement using a different (compatible)

INTO

clause, no rows are lost.

When you declare a cursor variable as the formal parameter of a subprogram that fetches from the cursor variable, you must specify the

IN OUT

mode. If the subprogram also opens the cursor variable, you must specify the

IN OUT

mode.

If you try to fetch from a closed or never-opened cursor variable, PL/SQL raises the predefined exception

INVALID_CURSOR

Closing a Cursor Variable

The

statement disables a cursor variable and makes the associated result set undefined. Close the cursor variable after the last row is processed.

When declaring a cursor variable as the formal parameter of a subprogram that closes the cursor variable, you must specify the

IN OUT

mode. If you try to close an already-closed or never-opened cursor variable, PL/SQL raises the predefined exception

INVALID_CURSOR

Reducing Network Traffic When Passing Host Cursor Variables to PL/SQL

When passing host cursor variables to PL/SQL, you can reduce network traffic by grouping

OPEN-FOR

statements. For example, the following PL/SQL block opens multiple cursor variables in a single round trip:

/* anonymous PL/SQL block in host environment */

BEGIN

OPEN :emp_cv FOR SELECT * FROM employees;

OPEN :dept_cv FOR SELECT * FROM departments;

OPEN :loc_cv FOR SELECT * FROM locations;

END;

This technique might be useful in Oracle Forms, for instance, when you want to populate a multi-block form. When you pass host cursor variables to a PL/SQL block for opening, the query work areas to which they point remain accessible after the block completes, so your OCI or Pro*C program can use these work areas for ordinary cursor operations. For example, you open several such work areas in a single round trip:

BEGIN

OPEN :c1 FOR SELECT 1 FROM dual;

OPEN :c2 FOR SELECT 1 FROM dual;

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Using Cursor Variables (REF CURSORs)

OPEN :c3 FOR SELECT 1 FROM dual;

END;

The cursors assigned to c1

, c2

, and c3

behave normally, and you can use them for any purpose. When finished, release the cursors as follows:

BEGIN

CLOSE :c1; CLOSE :c2; CLOSE :c3;

END;

Avoiding Errors with Cursor Variables

If both cursor variables involved in an assignment are strongly typed, they must have exactly the same datatype (not just the same return type). If one or both cursor variables are weakly typed, they can have different datatypes.

If you try to fetch from, close, or refer to cursor attributes of a cursor variable that does not point to a query work area, PL/SQL raises the

INVALID_CURSOR

exception. You can make a cursor variable (or parameter) point to a query work area in two ways:

■

OPEN

the cursor variable

FOR

the query.

Assign to the cursor variable the value of an already

OPEN ed host cursor variable or PL/SQL cursor variable.

If you assign an unopened cursor variable to another cursor variable, the second one remains invalid even after you open the first one.

Be careful when passing cursor variables as parameters. At run time, PL/SQL raises

ROWTYPE_MISMATCH

if the return types of the actual and formal parameters are incompatible.

Restrictions on Cursor Variables

Currently, cursor variables are subject to the following restrictions:

■

You cannot declare cursor variables in a package specification, as illustrated in

Example 6–34 .

If you bind a host cursor variable into PL/SQL from an OCI client, you cannot fetch from it on the server side unless you also open it there on the same server call.

You cannot use comparison operators to test cursor variables for equality, inequality, or nullity.

Database columns cannot store the values of cursor variables. There is no equivalent type to use in a

CREATE TABLE

statement.

You cannot store cursor variables in an associative array, nested table, or varray.

Cursors and cursor variables are not interoperable; that is, you cannot use one where the other is expected. For example, you cannot reference a cursor variable in a cursor

FOR

loop.

Example 6–34 Declaration of Cursor Variables in a Package

CREATE PACKAGE emp_data AS

TYPE EmpCurTyp IS REF CURSOR RETURN employees%ROWTYPE;

-- emp_cv EmpCurTyp; -- not allowed

Performing SQL Operations from PL/SQL

6-27

Using Cursor Expressions

PROCEDURE open_emp_cv;

END emp_data;

CREATE PACKAGE BODY emp_data AS

-- emp_cv EmpCurTyp; -- not allowed

PROCEDURE open_emp_cv IS

emp_cv EmpCurTyp; -- this is legal

BEGIN

OPEN emp_cv FOR SELECT * FROM employees;

END open_emp_cv;

END emp_data;

Note:

■

Using a

REF CURSOR

variable in a server-to-server RPC results in an error. However, a

REF CURSOR

variable is permitted in a server-to-server RPC if the remote database is a non-Oracle database accessed through a Procedural Gateway.

LOB parameters are not permitted in a server-to-server RPC.

Using Cursor Expressions

A cursor expression returns a nested cursor. Each row in the result set can contain values as usual, plus cursors produced by subqueries involving the other values in the row. A single query can return a large set of related values retrieved from multiple tables. You can process the result set with nested loops that fetch first from the rows of the result set, then from any nested cursors within those rows.

PL/SQL supports queries with cursor expressions as part of cursor declarations,

REF

CURSOR

declarations and ref cursor variables. You can also use cursor expressions in dynamic SQL queries. Here is the syntax:

CURSOR(

subquery

)

A nested cursor is implicitly opened when the containing row is fetched from the parent cursor. The nested cursor is closed only when:

■

The nested cursor is explicitly closed by the user

The parent cursor is reexecuted

■

The parent cursor is closed

The parent cursor is canceled

An error arises during a fetch on one of its parent cursors. The nested cursor is closed as part of the clean-up.

Restrictions on Cursor Expressions

The following are restrictions on cursor expressions:

■

You cannot use a cursor expression with an implicit cursor.

Cursor expressions can appear only:

■

In a

SELECT

statement that is not nested in any other query expression, except when it is a subquery of the cursor expression itself.

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Using Cursor Expressions

■

As arguments to table functions, in the

FROM

clause of a

SELECT

statement.

Cursor expressions can appear only in the outermost

SELECT

list of the query specification.

Cursor expressions cannot appear in view declarations.

You cannot perform

BIND

and

EXECUTE

operations on cursor expressions.

Example of Cursor Expressions

Example 6–35 , we find a specified location ID, and a cursor from which we can fetch

all the departments in that location. As we fetch each department's name, we also get another cursor that lets us fetch their associated employee details from another table.

Example 6–35 Using a Cursor Expression

DECLARE

TYPE emp_cur_typ IS REF CURSOR;

emp_cur emp_cur_typ;

dept_name departments.department_name%TYPE;

emp_name employees.last_name%TYPE;

CURSOR c1 IS SELECT

department_name,

-- second item in the result set is another result set,

-- which is represented as a ref cursor and labelled "employees".

CURSOR

( SELECT e.last_name FROM employees e

WHERE e.department_id = d.department_id) employees

FROM departments d WHERE department_name like 'A%';

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO dept_name, emp_cur;

EXIT WHEN c1%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('Department: ' || dept_name);

-- for each row in the result set, the result set from a subquery is processed

-- the set could be passed to a procedure for processing rather than the loop

LOOP

FETCH emp_cur INTO emp_name;

EXIT WHEN emp_cur%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('-- Employee: ' || emp_name);

END LOOP;

CLOSE c1;

END;

Constructing REF CURSORs with Cursor Subqueries

You can use cursor subqueries, also know as cursor expressions, to pass sets of rows as parameters to functions. For example, this statement passes a parameter to the

StockPivot function consisting of a

REF CURSOR

that represents the rows returned by the cursor subquery:

SELECT * FROM TABLE(StockPivot(

CURSOR(SELECT * FROM StockTable)));

Cursor subqueries are often used with table functions, which are explained in

"Setting

Up Transformations with Pipelined Functions" on page 11-31.

Performing SQL Operations from PL/SQL

6-29

Overview of Transaction Processing in PL/SQL

This section explains transaction processing with PL/SQL using SQL

COMMIT

SAVEPOINT

, and

ROLLBACK

statements that ensure the consistency of a database. You can include these SQL statements directly in your PL/SQL programs. Transaction processing is an Oracle feature, available through all programming languages, that lets multiple users work on the database concurrently, and ensures that each user sees a consistent version of data and that all changes are applied in the right order.

You usually do not need to write extra code to prevent problems with multiple users accessing data concurrently. Oracle uses locks to control concurrent access to data, and locks only the minimum amount of data necessary, for as little time as possible. You can request locks on tables or rows if you really do need this level of control. You can choose from several modes of locking such as row share

and exclusive

For information on transactions, see Oracle Database Concepts. For information on the

SQL

COMMIT

SAVEPOINT

, and

ROLLBACK

statements, see the Oracle Database SQL

Reference.

Using COMMIT in PL/SQL

The

COMMIT

statement ends the current transaction, making any changes made during that transaction permanent, and visible to other users. Transactions are not tied to

PL/SQL

BEGIN-END

blocks. A block can contain multiple transactions, and a transaction can span multiple blocks.

Example 6–36 illustrates a transaction that transfers money from one bank account to

another. It is important that the money come out of one account, and into the other, at exactly the same moment. Otherwise, a problem partway through might make the money be lost from both accounts or be duplicated in both accounts.

Example 6–36 Using COMMIT With the WRITE Clause

CREATE TABLE accounts (account_id NUMBER(6), balance NUMBER (10,2));

INSERT INTO accounts VALUES (7715, 6350.00);

INSERT INTO accounts VALUES (7720, 5100.50);

DECLARE

transfer NUMBER(8,2) := 250;

BEGIN

UPDATE accounts SET balance = balance - transfer WHERE account_id = 7715;

UPDATE accounts SET balance = balance + transfer WHERE account_id = 7720;

COMMIT COMMENT 'Transfer From 7715 to 7720' WRITE IMMEDIATE NOWAIT;

END;

The optional

COMMENT

clause lets you specify a comment to be associated with a distributed transaction. If a network or machine fails during the commit, the state of the distributed transaction might be unknown or in doubt. In that case, Oracle stores the text specified by

COMMENT

in the data dictionary along with the transaction ID.

Asynchronous commit provides more control for the user with the

WRITE

clause. This option specifies the priority with which the redo information generated by the commit operation is written to the redo log.

For more information on using

COMMIT

, see "Committing Transactions" in Oracle

Database Application Developer's Guide - Fundamentals. For information about

distributed transactions, see Oracle Database Concepts. See also "COMMIT Statement" on page 13-24.

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Overview of Transaction Processing in PL/SQL

Using ROLLBACK in PL/SQL

The

ROLLBACK

statement ends the current transaction and undoes any changes made during that transaction. If you make a mistake, such as deleting the wrong row from a table, a rollback restores the original data. If you cannot finish a transaction because an exception is raised or a SQL statement fails, a rollback lets you take corrective action and perhaps start over.

Example 6–37 inserts information about an employee into three different database

tables. If an

INSERT

statement tries to store a duplicate employee number, the predefined exception

DUP_VAL_ON_INDEX

is raised. To make sure that changes to all three tables are undone, the exception handler executes a

ROLLBACK

Example 6–37 Using ROLLBACK

CREATE TABLE emp_name AS SELECT employee_id, last_name FROM employees;

CREATE UNIQUE INDEX empname_ix ON emp_name (employee_id);

CREATE TABLE emp_sal AS SELECT employee_id, salary FROM employees;

CREATE UNIQUE INDEX empsal_ix ON emp_sal (employee_id);

CREATE TABLE emp_job AS SELECT employee_id, job_id FROM employees;

CREATE UNIQUE INDEX empjobid_ix ON emp_job (employee_id);

DECLARE

emp_id NUMBER(6);

emp_lastname VARCHAR2(25);

emp_salary NUMBER(8,2);

emp_jobid VARCHAR2(10);

BEGIN

SELECT employee_id, last_name, salary, job_id INTO emp_id, emp_lastname,

emp_salary, emp_jobid FROM employees WHERE employee_id = 120;

INSERT INTO emp_name VALUES (emp_id, emp_lastname);

INSERT INTO emp_sal VALUES (emp_id, emp_salary);

INSERT INTO emp_job VALUES (emp_id, emp_jobid);

EXCEPTION

WHEN DUP_VAL_ON_INDEX THEN

ROLLBACK;

DBMS_OUTPUT.PUT_LINE('Inserts have been rolled back');

END;

Using SAVEPOINT in PL/SQL

SAVEPOINT

names and marks the current point in the processing of a transaction.

Savepoints let you roll back part of a transaction instead of the whole transaction. The number of active savepoints for each session is unlimited.

Example 6–38 marks a savepoint before doing an insert. If the

INSERT

statement tries to store a duplicate value in the employee_id

column, the predefined exception

DUP_VAL_ON_INDEX

is raised. In that case, you roll back to the savepoint, undoing just the insert.

Example 6–38 Using SAVEPOINT With ROLLBACK

CREATE TABLE emp_name AS SELECT employee_id, last_name, salary FROM employees;

CREATE UNIQUE INDEX empname_ix ON emp_name (employee_id);

DECLARE

emp_id employees.employee_id%TYPE;

Performing SQL Operations from PL/SQL

6-31

Overview of Transaction Processing in PL/SQL

emp_lastname employees.last_name%TYPE;

emp_salary employees.salary%TYPE;

BEGIN

SELECT employee_id, last_name, salary INTO emp_id, emp_lastname,

emp_salary FROM employees WHERE employee_id = 120;

UPDATE emp_name SET salary = salary * 1.1 WHERE employee_id = emp_id;

DELETE FROM emp_name WHERE employee_id = 130;

SAVEPOINT do_insert;

INSERT INTO emp_name VALUES (emp_id, emp_lastname, emp_salary);

EXCEPTION

WHEN DUP_VAL_ON_INDEX THEN

ROLLBACK TO do_insert;

DBMS_OUTPUT.PUT_LINE('Insert has been rolled back');

END;

When you roll back to a savepoint, any savepoints marked after that savepoint are erased. The savepoint to which you roll back is not erased. A simple rollback or commit erases all savepoints.

If you mark a savepoint within a recursive subprogram, new instances of the

SAVEPOINT

statement are executed at each level in the recursive descent, but you can only roll back to the most recently marked savepoint.

Savepoint names are undeclared identifiers. Reusing a savepoint name within a transaction moves the savepoint from its old position to the current point in the transaction. This means that a rollback to the savepoint affects only the current part of your transaction, as shown in

Example 6–39

Example 6–39 Reusing a SAVEPOINT With ROLLBACK

CREATE TABLE emp_name AS SELECT employee_id, last_name, salary FROM employees;

CREATE UNIQUE INDEX empname_ix ON emp_name (employee_id);

DECLARE

emp_id employees.employee_id%TYPE;

emp_lastname employees.last_name%TYPE;

emp_salary employees.salary%TYPE;

BEGIN

SELECT employee_id, last_name, salary INTO emp_id, emp_lastname,

emp_salary FROM employees WHERE employee_id = 120;

SAVEPOINT my_savepoint;

UPDATE emp_name SET salary = salary * 1.1 WHERE employee_id = emp_id;

DELETE FROM emp_name WHERE employee_id = 130;

SAVEPOINT my_savepoint; -- move my_savepoint to current poin

INSERT INTO emp_name VALUES (emp_id, emp_lastname, emp_salary);

EXCEPTION

WHEN DUP_VAL_ON_INDEX THEN

ROLLBACK TO my_savepoint;

DBMS_OUTPUT.PUT_LINE('Transaction rolled back.');

END;

How Oracle Does Implicit Rollbacks

Before executing an

INSERT

UPDATE

, or

DELETE

statement, Oracle marks an implicit savepoint (unavailable to you). If the statement fails, Oracle rolls back to the savepoint.

Usually, just the failed SQL statement is rolled back, not the whole transaction. If the

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Overview of Transaction Processing in PL/SQL statement raises an unhandled exception, the host environment determines what is rolled back.

Oracle can also roll back single SQL statements to break deadlocks. Oracle signals an error to one of the participating transactions and rolls back the current statement in that transaction.

Before executing a SQL statement, Oracle must parse it, that is, examine it to make sure it follows syntax rules and refers to valid schema objects. Errors detected while executing a SQL statement cause a rollback, but errors detected while parsing the statement do not.

If you exit a stored subprogram with an unhandled exception, PL/SQL does not assign values to

OUT

parameters, and does not do any rollback.

Ending Transactions

You should explicitly commit or roll back every transaction. Whether you issue the commit or rollback in your PL/SQL program or from a client program depends on the application logic. If you do not commit or roll back a transaction explicitly, the client environment determines its final state.

For example, in the SQL*Plus environment, if your PL/SQL block does not include a

COMMIT

ROLLBACK

statement, the final state of your transaction depends on what you do after running the block. If you execute a data definition, data control, or

COMMIT

statement or if you issue the

EXIT

DISCONNECT

, or

QUIT

command, Oracle commits the transaction. If you execute a

ROLLBACK

statement or abort the SQL*Plus session, Oracle rolls back the transaction.

Setting Transaction Properties with SET TRANSACTION

You use the

SET TRANSACTION

statement to begin a read-only or read-write transaction, establish an isolation level, or assign your current transaction to a specified rollback segment. Read-only transactions are useful for running multiple queries while other users update the same tables.

During a read-only transaction, all queries refer to the same snapshot of the database, providing a multi-table, multi-query, read-consistent view. Other users can continue to query or update data as usual. A commit or rollback ends the transaction. In

Example 6–40 a store manager uses a read-only transaction to gather order totals for

the day, the past week, and the past month. The totals are unaffected by other users updating the database during the transaction.

Example 6–40 Using SET TRANSACTION to Begin a Read-only Transaction

DECLARE

daily_order_total NUMBER(12,2);

weekly_order_total NUMBER(12,2);

monthly_order_total NUMBER(12,2);

BEGIN

COMMIT; -- ends previous transaction

SET TRANSACTION READ ONLY NAME 'Calculate Order Totals';

SELECT SUM (order_total) INTO daily_order_total FROM orders

WHERE order_date = SYSDATE;

SELECT SUM (order_total) INTO weekly_order_total FROM orders

WHERE order_date = SYSDATE - 7;

SELECT SUM (order_total) INTO monthly_order_total FROM orders

WHERE order_date = SYSDATE - 30;

COMMIT; -- ends read-only transaction

Performing SQL Operations from PL/SQL

6-33

Overview of Transaction Processing in PL/SQL

END;

The

SET TRANSACTION

statement must be the first SQL statement in a read-only transaction and can only appear once in a transaction. If you set a transaction to

READ

ONLY

, subsequent queries see only changes committed before the transaction began.

The use of

READ ONLY

does not affect other users or transactions.

Restrictions on SET TRANSACTION

Only the

SELECT INTO

OPEN

FETCH

LOCK TABLE

COMMIT

, and

ROLLBACK statements are allowed in a read-only transaction. Queries cannot be

FOR UPDATE

Overriding Default Locking

By default, Oracle locks data structures for you automatically, which is a major strength of the Oracle database: different applications can read and write to the same data without harming each other's data or coordinating with each other.

You can request data locks on specific rows or entire tables if you need to override default locking. Explicit locking lets you deny access to data for the duration of a transaction.:

■

With the

LOCK TABLE

statement, you can explicitly lock entire tables.

■

With the

SELECT FOR UPDATE

statement, you can explicitly lock specific rows of a table to make sure they do not change after you have read them. That way, you can check which or how many rows will be affected by an

UPDATE

DELETE statement before issuing the statement, and no other application can change the rows in the meantime.

Using FOR UPDATE

When you declare a cursor that will be referenced in the

CURRENT OF

clause of an

UPDATE

DELETE

statement, you must use the

FOR UPDATE

clause to acquire exclusive row locks. An example follows:

DECLARE

CURSOR c1 IS SELECT employee_id, salary FROM employees

WHERE job_id = 'SA_REP' AND commission_pct > .10

FOR UPDATE NOWAIT;

The

SELECT

...

FOR UPDATE

statement identifies the rows that will be updated or deleted, then locks each row in the result set. This is useful when you want to base an update on the existing values in a row. In that case, you must make sure the row is not changed by another user before the update.

The optional keyword

NOWAIT

tells Oracle not to wait if requested rows have been locked by another user. Control is immediately returned to your program so that it can do other work before trying again to acquire the lock. If you omit the keyword

NOWAIT

, Oracle waits until the rows are available.

All rows are locked when you open the cursor, not as they are fetched. The rows are unlocked when you commit or roll back the transaction. Since the rows are no longer locked, you cannot fetch from a

FOR UPDATE

cursor after a commit. For a workaround,

see "Fetching Across Commits" on page 6-35.

When querying multiple tables, you can use the

FOR UPDATE

clause to confine row locking to particular tables. Rows in a table are locked only if the

FOR UPDATE OF

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Oracle Database PL/SQL User’s Guide and Reference

Overview of Transaction Processing in PL/SQL clause refers to a column in that table. For example, the following query locks rows in the employees

table but not in the departments

table:

DECLARE

CURSOR c1 IS SELECT last_name, department_name FROM employees, departments

WHERE employees.department_id = departments.department_id

AND job_id = 'SA_MAN'

FOR UPDATE OF salary;

As shown in

Example 6–41 , you use the

CURRENT OF

clause in an

UPDATE

DELETE statement to refer to the latest row fetched from a cursor.

Example 6–41 Using CURRENT OF to Update the Latest Row Fetched From a Cursor

DECLARE

my_emp_id NUMBER(6);

my_job_id VARCHAR2(10);

my_sal NUMBER(8,2);

CURSOR c1 IS SELECT employee_id, job_id, salary FROM employees FOR UPDATE;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO my_emp_id, my_job_id, my_sal;

IF my_job_id = 'SA_REP' THEN

UPDATE employees SET salary = salary * 1.02 WHERE CURRENT OF c1;

END IF;

EXIT WHEN c1%NOTFOUND;

END LOOP;

END;

Using LOCK TABLE

You use the

LOCK TABLE

statement to lock entire database tables in a specified lock mode so that you can share or deny access to them. Row share locks allow concurrent access to a table; they prevent other users from locking the entire table for exclusive use. Table locks are released when your transaction issues a commit or rollback.

LOCK TABLE employees IN ROW SHARE MODE NOWAIT;

The lock mode determines what other locks can be placed on the table. For example, many users can acquire row share locks on a table at the same time, but only one user at a time can acquire an exclusive lock. While one user has an exclusive lock on a table, no other users can insert, delete, or update rows in that table. For more information about lock modes, see Oracle Database Application Developer's Guide - Fundamentals.

A table lock never keeps other users from querying a table, and a query never acquires a table lock. Only if two different transactions try to modify the same row will one transaction wait for the other to complete.

Fetching Across Commits

PL/SQL raises an exception if you try to fetch from a

FOR UPDATE

cursor after doing a commit. The

FOR UPDATE

clause locks the rows when you open the cursor, and unlocks them when you commit.

DECLARE

-- if "FOR UPDATE OF salary" is included on following line, an error is raised

CURSOR c1 IS SELECT * FROM employees;

emp_rec employees%ROWTYPE;

BEGIN

OPEN c1;

Performing SQL Operations from PL/SQL

6-35

Overview of Transaction Processing in PL/SQL

LOOP

FETCH c1 INTO emp_rec; -- FETCH fails on the second iteration with FOR UPDATE

EXIT WHEN c1%NOTFOUND;

IF emp_rec.employee_id = 105 THEN

UPDATE employees SET salary = salary * 1.05 WHERE employee_id = 105;

END IF;

COMMIT; -- releases locks

END LOOP;

END;

If you want to fetch across commits, use the

ROWID

pseudocolumn to mimic the

CURRENT OF

clause. Select the rowid of each row into a

UROWID

variable, then use the rowid to identify the current row during subsequent updates and deletes.

Example 6–42 Fetching Across COMMITs Using ROWID

DECLARE

CURSOR c1 IS SELECT last_name, job_id, rowid FROM employees;

my_lastname employees.last_name%TYPE;

my_jobid employees.job_id%TYPE;

my_rowid UROWID;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO my_lastname, my_jobid, my_rowid;

EXIT WHEN c1%NOTFOUND;

UPDATE employees SET salary = salary * 1.02 WHERE rowid = my_rowid;

-- this mimics WHERE CURRENT OF c1

COMMIT;

END LOOP;

CLOSE c1;

END;

Because the fetched rows are not locked by a

FOR UPDATE

clause, other users might unintentionally overwrite your changes. The extra space needed for read consistency is not released until the cursor is closed, which can slow down processing for large updates.

The next example shows that you can use the

%ROWTYPE

attribute with cursors that reference the

ROWID

pseudocolumn:

DECLARE

CURSOR c1 IS SELECT employee_id, last_name, salary, rowid FROM employees;

emp_rec c1%ROWTYPE;

BEGIN

OPEN c1;

LOOP

FETCH c1 INTO emp_rec;

EXIT WHEN c1%NOTFOUND;

IF emp_rec.salary = 0 THEN

DELETE FROM employees WHERE rowid = emp_rec.rowid;

END IF;

END LOOP;

CLOSE c1;

END;

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Oracle Database PL/SQL User’s Guide and Reference

Doing Independent Units of Work with Autonomous Transactions

An autonomous transaction is an independent transaction started by another transaction, the main transaction. Autonomous transactions do SQL operations and commit or roll back, without committing or rolling back the main transaction. For example, if you write auditing data to a log table, you want to commit the audit data even if the operation you are auditing later fails; if something goes wrong recording the audit data, you do not want the main operation to be rolled back.

Figure 6–1

shows how control flows from the main transaction (MT) to an autonomous transaction (AT) and back again.

Figure 6–1 Transaction Control Flow

Main Transaction Autonomous Transaction

PROCEDURE proc1 IS

emp_id NUMBER;

BEGIN

emp_id := 7788;

INSERT ...

MT begins

SELECT ...

proc2;

DELETE ...

COMMIT;

MT ends

END;

PROCEDURE proc2 IS

PRAGMA AUTON...

dept_id NUMBER;

BEGIN

MT suspends

dept_id := 20;

UPDATE ...

AT begins

INSERT ...

UPDATE ...

COMMIT;

AT ends

END;

MT resumes

Advantages of Autonomous Transactions

Once started, an autonomous transaction is fully independent. It shares no locks, resources, or commit-dependencies with the main transaction. You can log events, increment retry counters, and so on, even if the main transaction rolls back.

More important, autonomous transactions help you build modular, reusable software components. You can encapsulate autonomous transactions within stored procedures.

A calling application does not need to know whether operations done by that stored procedure succeeded or failed.

Defining Autonomous Transactions

To define autonomous transactions, you use the pragma (compiler directive)

AUTONOMOUS_TRANSACTION

. The pragma instructs the PL/SQL compiler to mark a routine as autonomous (independent). In this context, the term routine includes

■

Top-level (not nested) anonymous PL/SQL blocks

Local, standalone, and packaged functions and procedures

Methods of a SQL object type

Database triggers

You can code the pragma anywhere in the declarative section of a routine. But, for readability, code the pragma at the top of the section. The syntax is

PRAGMA

AUTONOMOUS_TRANSACTION

Example 6–43 marks a packaged function as autonomous. You cannot use the pragma

to mark all subprograms in a package (or all methods in an object type) as autonomous. Only individual routines can be marked autonomous.

Performing SQL Operations from PL/SQL

6-37

Doing Independent Units of Work with Autonomous Transactions

Example 6–43 Declaring an Autonomous Function in a Package

CREATE OR REPLACE PACKAGE emp_actions AS -- package specification

FUNCTION raise_salary (emp_id NUMBER, sal_raise NUMBER) RETURN NUMBER;

END emp_actions;

CREATE OR REPLACE PACKAGE BODY emp_actions AS -- package body

-- code for function raise_salary

FUNCTION raise_salary (emp_id NUMBER, sal_raise NUMBER) RETURN NUMBER IS

PRAGMA AUTONOMOUS_TRANSACTION;

new_sal NUMBER(8,2);

BEGIN

UPDATE employees SET salary = salary + sal_raise WHERE employee_id = emp_id;

COMMIT;

SELECT salary INTO new_sal FROM employees WHERE employee_id = emp_id;

RETURN new_sal;

END raise_salary;

END emp_actions;

Example 6–44 marks a standalone procedure as autonomous.

Example 6–44 Declaring an Autonomous Standalone Procedure

CREATE PROCEDURE lower_salary (emp_id NUMBER, amount NUMBER) AS

PRAGMA AUTONOMOUS_TRANSACTION;

BEGIN

UPDATE employees SET salary = salary - amount WHERE employee_id = emp_id;

COMMIT;

END lower_salary;

Example 6–45 marks a PL/SQL block as autonomous. However, you cannot mark a

nested PL/SQL block as autonomous.

Example 6–45 Declaring an Autonomous PL/SQL Block

DECLARE

PRAGMA AUTONOMOUS_TRANSACTION;

emp_id NUMBER(6);

amount NUMBER(6,2);

BEGIN

emp_id := 200;

amount := 200;

UPDATE employees SET salary = salary - amount WHERE employee_id = emp_id;

COMMIT;

END;

Example 6–46 marks a database trigger as autonomous. Unlike regular triggers,

autonomous triggers can contain transaction control statements such as

COMMIT

and

ROLLBACK

Example 6–46 Declaring an Autonomous Trigger

CREATE TABLE emp_audit ( emp_audit_id NUMBER(6), up_date DATE,

new_sal NUMBER(8,2), old_sal NUMBER(8,2) );

CREATE OR REPLACE TRIGGER audit_sal

AFTER UPDATE OF salary ON employees FOR EACH ROW

DECLARE

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Oracle Database PL/SQL User’s Guide and Reference

Doing Independent Units of Work with Autonomous Transactions

PRAGMA AUTONOMOUS_TRANSACTION

;

BEGIN

-- bind variables are used here for values

INSERT INTO emp_audit VALUES( :old.employee_id, SYSDATE,

:new.salary, :old.salary );

COMMIT;

END;

■

Comparison of Autonomous Transactions and Nested Transactions

Although an autonomous transaction is started by another transaction, it is not a nested transaction:

It does not share transactional resources (such as locks) with the main transaction.

It does not depend on the main transaction. For example, if the main transaction rolls back, nested transactions roll back, but autonomous transactions do not.

Its committed changes are visible to other transactions immediately. (A nested transaction's committed changes are not visible to other transactions until the main transaction commits.)

Exceptions raised in an autonomous transaction cause a transaction-level rollback, not a statement-level rollback.

Transaction Context

The main transaction shares its context with nested routines, but not with autonomous transactions. When one autonomous routine calls another (or itself recursively), the routines share no transaction context. When an autonomous routine calls a non-autonomous routine, the routines share the same transaction context.

Transaction Visibility

Changes made by an autonomous transaction become visible to other transactions when the autonomous transaction commits. These changes become visible to the main transaction when it resumes, if its isolation level is set to

READ COMMITTED

(the default).

If you set the isolation level of the main transaction to

SERIALIZABLE

, changes made by its autonomous transactions are not visible to the main transaction when it resumes:

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

Controlling Autonomous Transactions

The first SQL statement in an autonomous routine begins a transaction. When one transaction ends, the next SQL statement begins another transaction. All SQL statements executed since the last commit or rollback make up the current transaction.

To control autonomous transactions, use the following statements, which apply only to the current (active) transaction:

■

COMMIT

■

ROLLBACK [TO savepoint_name]

SAVEPOINT savepoint_name

SET TRANSACTION

Performing SQL Operations from PL/SQL

6-39

Doing Independent Units of Work with Autonomous Transactions

Note:

■

Transaction properties set in the main transaction apply only to that transaction, not to its autonomous transactions, and vice versa.

Cursor attributes are not affected by autonomous transactions.

Entering and Exiting

When you enter the executable section of an autonomous routine, the main transaction suspends. When you exit the routine, the main transaction resumes.

To exit normally, you must explicitly commit or roll back all autonomous transactions.

If the routine (or any routine called by it) has pending transactions, an exception is raised, and the pending transactions are rolled back.

Committing and Rolling Back

COMMIT

and

ROLLBACK

end the active autonomous transaction but do not exit the autonomous routine. When one transaction ends, the next SQL statement begins another transaction. A single autonomous routine could contain several autonomous transactions, if it issued several

COMMIT

statements.

Using Savepoints

The scope of a savepoint is the transaction in which it is defined. Savepoints defined in the main transaction are unrelated to savepoints defined in its autonomous transactions. In fact, the main transaction and an autonomous transaction can use the same savepoint names.

You can roll back only to savepoints marked in the current transaction. In an autonomous transaction, you cannot roll back to a savepoint marked in the main transaction. To do so, you must resume the main transaction by exiting the autonomous routine.

When in the main transaction, rolling back to a savepoint marked before you started an autonomous transaction does not roll back the autonomous transaction. Remember, autonomous transactions are fully independent of the main transaction.

Avoiding Errors with Autonomous Transactions

To avoid some common errors, keep the following points in mind:

■

If an autonomous transaction attempts to access a resource held by the main transaction, a deadlock can occur. Oracle raises an exception in the autonomous transaction, which is rolled back if the exception goes unhandled.

The Oracle initialization parameter

TRANSACTIONS

specifies the maximum number of concurrent transactions. That number might be exceeded because an autonomous transaction runs concurrently with the main transaction.

If you try to exit an active autonomous transaction without committing or rolling back, Oracle raises an exception. If the exception goes unhandled, the transaction is rolled back.

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Doing Independent Units of Work with Autonomous Transactions

Using Autonomous Triggers

Among other things, you can use database triggers to log events transparently.

Suppose you want to track all inserts into a table, even those that roll back. In

Example 6–47 , you use a trigger to insert duplicate rows into a shadow table. Because

it is autonomous, the trigger can commit changes to the shadow table whether or not you commit changes to the main table.

Example 6–47 Using Autonomous Triggers

CREATE TABLE emp_audit ( emp_audit_id NUMBER(6), up_date DATE,

new_sal NUMBER(8,2), old_sal NUMBER(8,2) );

-- create an autonomous trigger that inserts into the audit table before

-- each update of salary in the employees table

CREATE OR REPLACE TRIGGER audit_sal

BEFORE UPDATE OF salary ON employees FOR EACH ROW

DECLARE

PRAGMA AUTONOMOUS_TRANSACTION

;

BEGIN

INSERT INTO emp_audit VALUES( :old.employee_id, SYSDATE,

:new.salary, :old.salary );

COMMIT;

END;

-- update the salary of an employee, and then commit the insert

UPDATE employees SET salary = salary * 1.05 WHERE employee_id = 115;

COMMIT;

-- update another salary, then roll back the update

UPDATE employees SET salary = salary * 1.05 WHERE employee_id = 116;

ROLLBACK;

-- show that both committed and rolled-back updates add rows to audit table

SELECT * FROM emp_audit WHERE emp_audit_id = 115 OR emp_audit_id = 116;

Unlike regular triggers, autonomous triggers can execute DDL statements using native

dynamic SQL, discussed in Chapter 7, "Performing SQL Operations with Native

Dynamic SQL" . In the following example, trigger

drop_temp_table

drops a temporary database table after a row is inserted in table emp_audit

CREATE TABLE emp_audit ( emp_audit_id NUMBER(6), up_date DATE,

new_sal NUMBER(8,2), old_sal NUMBER(8,2) );

CREATE TABLE temp_audit ( emp_audit_id NUMBER(6), up_date DATE);

CREATE OR REPLACE TRIGGER drop_temp_table

AFTER INSERT ON emp_audit

DECLARE

PRAGMA AUTONOMOUS_TRANSACTION

;

BEGIN

EXECUTE IMMEDIATE 'DROP TABLE temp_audit';

COMMIT;

END;

For more information about database triggers, see Oracle Database Application

Developer's Guide - Fundamentals.

Performing SQL Operations from PL/SQL

6-41

Doing Independent Units of Work with Autonomous Transactions

Calling Autonomous Functions from SQL

A function called from SQL statements must obey certain rules meant to control side

effects. See "Controlling Side Effects of PL/SQL Subprograms" on page 8-23. To check

for violations of the rules, you can use the pragma

RESTRICT_REFERENCES

. The pragma asserts that a function does not read or write database tables or package variables. For more information, See Oracle Database Application Developer's Guide -

Fundamentals.

However, by definition, autonomous routines never violate the rules read no database state (RNDS)

and write no database state (WNDS)

no matter what they do. This can be useful, as

Example 6–48 shows. When you call the packaged

function log_msg

from a query, it inserts a message into database table debug_output

without violating the rule write no database state

Example 6–48 Calling an Autonomous Function

-- create the debug table

CREATE TABLE debug_output (msg VARCHAR2(200));

-- create the package spec

CREATE PACKAGE debugging AS

FUNCTION log_msg (msg VARCHAR2) RETURN VARCHAR2;

PRAGMA RESTRICT_REFERENCES(log_msg, WNDS, RNDS);

END debugging;

-- create the package body

CREATE PACKAGE BODY debugging AS

FUNCTION log_msg (msg VARCHAR2) RETURN VARCHAR2 IS

PRAGMA AUTONOMOUS_TRANSACTION;

BEGIN

-- the following insert does not violate the constraint

-- WNDS because this is an autonomous routine

INSERT INTO debug_output VALUES (msg);

COMMIT;

RETURN msg;

END;

END debugging;

-- call the packaged function from a query

DECLARE

my_emp_id NUMBER(6);

my_last_name VARCHAR2(25);

my_count NUMBER;

BEGIN

my_emp_id := 120;

SELECT debugging.log_msg(last_name) INTO my_last_name FROM employees

WHERE employee_id = my_emp_id;

-- even if you roll back in this scope, the insert into 'debug_output' remains

-- committed because it is part of an autonomous transaction

ROLLBACK;

END;

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Oracle Database PL/SQL User’s Guide and Reference

Performing SQL Operations with Native

Dynamic SQL

This chapter describes how to use native dynamic SQL (dynamic SQL for short) with

PL/SQL to make your programs more flexible, by building and processing SQL statements at run time.

With dynamic SQL, you can directly execute most types of SQL statement, including data definition and data control statements. You can build statements in which you do not know table names,

WHERE

clauses, and other information in advance.

This chapter contains these topics:

■

Why Use Dynamic SQL with PL/SQL?

■

Using the EXECUTE IMMEDIATE Statement in PL/SQL

Using Bulk Dynamic SQL in PL/SQL

■

Guidelines for Using Dynamic SQL with PL/SQL

For additional information about dynamic SQL, see Oracle Database Application

Developer's Guide - Fundamentals.

Why Use Dynamic SQL with PL/SQL?

Dynamic SQL enables you to build SQL statements dynamically at runtime. You can create more general purpose, flexible applications by using dynamic SQL because the full text of a SQL statement may be unknown at compilation.

To process most dynamic SQL statements, you use the

EXECUTE IMMEDIATE statement. To process a multi-row query (

SELECT

statement), you use the

OPEN-FOR

FETCH

, and

statements.

You need dynamic SQL in the following situations:

■

You want to execute a SQL data definition statement (such as

CREATE

), a data control statement (such as

GRANT

), or a session control statement (such as

ALTER

SESSION

). Unlike

INSERT

UPDATE

, and

DELETE

statements, these statements cannot be included directly in a PL/SQL program.

You want more flexibility. For example, you might want to pass the name of a schema object as a parameter to a procedure. You might want to build different search conditions for the

WHERE

clause of a

SELECT

statement.

You want to issue a query where you do not know the number, names, or datatypes of the columns in advance. In this case, you use the

DBMS_SQL

package rather than the

OPEN-FOR

statement.

Performing SQL Operations with Native Dynamic SQL

7-1

Using the EXECUTE IMMEDIATE Statement in PL/SQL

If you have older code that uses the

DBMS_SQL

package, the techniques described in this chapter using

EXECUTE IMMEDIATE

and

OPEN-FOR

generally provide better performance, more readable code, and extra features such as support for objects and collections.

For a comparison of dynamic SQL with

DBMS_SQL

, see Oracle Database Application

Developer's Guide - Fundamentals. For information on the

DBMS_SQL

package, see Oracle

Database PL/SQL Packages and Types Reference.

Note:

Native dynamic SQL using the

EXECUTE IMMEDIATE

and

OPEN-FOR

statements is faster and requires less coding than the

DBMS_SQL

package. However, the

DBMS_SQL

package should be used in these situations:

■

There is an unknown number of input or output variables, such as the number of column values returned by a query, that are used in a dynamic SQL statement (Method 4 for dynamic SQL).

The dynamic code is too large to fit inside a 32K bytes

VARCHAR2 variable.

Using the EXECUTE IMMEDIATE Statement in PL/SQL

The

EXECUTE IMMEDIATE

statement prepares (parses) and immediately executes a dynamic SQL statement or an anonymous PL/SQL block. The main argument to

EXECUTE IMMEDIATE

is the string containing the SQL statement to execute. You can build up the string using concatenation, or use a predefined string.

Except for multi-row queries, the dynamic string can contain any SQL statement or any PL/SQL block. The string can also contain placeholders, arbitrary names preceded by a colon, for bind arguments. In this case, you specify which PL/SQL variables correspond to the placeholders with the

INTO

USING

, and

RETURNING INTO

clauses.

When constructing a single SQL statement in a dynamic string, do not include a semicolon (;) at the end inside the quotation mark. When constructing a PL/SQL anonymous block, include the semicolon at the end of each PL/SQL statement and at the end of the anonymous block; there will be a semicolon immediately before the end of the string literal, and another following the closing single quotation mark.

You can only use placeholders in places where you can substitute variables in the SQL statement, such as conditional tests in

WHERE

clauses. You cannot use placeholders for

the names of schema objects. For the right way, see "Passing Schema Object Names As

Parameters" on page 7-8.

Used only for single-row queries, the

INTO

clause specifies the variables or record into which column values are retrieved. For each value retrieved by the query, there must be a corresponding, type-compatible variable or field in the

INTO

clause.

Used only for DML statements that have a

RETURNING

clause (without a

BULK

COLLECT

clause), the

RETURNING INTO

clause specifies the variables into which column values are returned. For each value returned by the DML statement, there must be a corresponding, type-compatible variable in the

RETURNING INTO

clause.

You can place all bind arguments in the

USING

clause. The default parameter mode is

. For DML statements that have a

RETURNING

clause, you can place

OUT

arguments in the

RETURNING INTO

clause without specifying the parameter mode. If you use both the

USING

clause and the

RETURNING INTO

clause, the

USING

clause can contain only

arguments.

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Using the EXECUTE IMMEDIATE Statement in PL/SQL

At run time, bind arguments replace corresponding placeholders in the dynamic string. Every placeholder must be associated with a bind argument in the

USING clause and/or

RETURNING INTO

clause. You can use numeric, character, and string literals as bind arguments, but you cannot use Boolean literals (

TRUE

FALSE

, and

NULL

). To pass nulls to the dynamic string, you must use a workaround. See

"Passing

Nulls to Dynamic SQL" on page 7-10.

Dynamic SQL supports all the SQL datatypes. For example, define variables and bind arguments can be collections,

LOB s, instances of an object type, and refs.

As a rule, dynamic SQL does not support PL/SQL-specific types. For example, define variables and bind arguments cannot be Booleans or associative arrays. The only exception is that a PL/SQL record can appear in the

INTO

clause.

You can execute a dynamic SQL statement repeatedly using new values for the bind arguments. However, you incur some overhead because

EXECUTE IMMEDIATE re-prepares the dynamic string before every execution.

For more information on

EXECUTE IMMEDIATE

, see

"EXECUTE IMMEDIATE

Statement" on page 13-41.

Example 7–1

illustrates several uses of dynamic SQL.

Example 7–1 Examples of Dynamic SQL

CREATE OR REPLACE PROCEDURE raise_emp_salary (column_value NUMBER,

emp_column VARCHAR2, amount NUMBER) IS

v_column VARCHAR2(30);

sql_stmt VARCHAR2(200);

BEGIN

-- determine if a valid column name has been given as input

SELECT COLUMN_NAME INTO v_column FROM USER_TAB_COLS

WHERE TABLE_NAME = 'EMPLOYEES' AND COLUMN_NAME = emp_column;

sql_stmt := 'UPDATE employees SET salary = salary + :1 WHERE '

|| v_column || ' = :2';

EXECUTE IMMEDIATE sql_stmt USING amount, column_value;

IF SQL%ROWCOUNT > 0 THEN

DBMS_OUTPUT.PUT_LINE('Salaries have been updated for: ' || emp_column

|| ' = ' || column_value);

END IF;

EXCEPTION

WHEN NO_DATA_FOUND THEN

DBMS_OUTPUT.PUT_LINE ('Invalid Column: ' || emp_column);

END raise_emp_salary;

DECLARE

plsql_block VARCHAR2(500);

BEGIN

-- note the semi-colons (;) inside the quotes '...'

plsql_block := 'BEGIN raise_emp_salary(:cvalue, :cname, :amt); END;';

EXECUTE IMMEDIATE plsql_block USING 110, 'DEPARTMENT_ID', 10;

EXECUTE IMMEDIATE 'BEGIN raise_emp_salary(:cvalue, :cname, :amt); END;'

USING 112, 'EMPLOYEE_ID', 10;

END;

DECLARE

sql_stmt VARCHAR2(200);

v_column VARCHAR2(30) := 'DEPARTMENT_ID';

dept_id NUMBER(4) := 46;

Performing SQL Operations with Native Dynamic SQL

7-3

Using the EXECUTE IMMEDIATE Statement in PL/SQL

dept_name VARCHAR2(30) := 'Special Projects';

mgr_id NUMBER(6) := 200;

loc_id NUMBER(4) := 1700;

BEGIN

-- note that there is no semi-colon (;) inside the quotes '...'

EXECUTE IMMEDIATE 'CREATE TABLE bonus (id NUMBER, amt NUMBER)';

sql_stmt := 'INSERT INTO departments VALUES (:1, :2, :3, :4)';

EXECUTE IMMEDIATE sql_stmt USING dept_id, dept_name, mgr_id, loc_id;

EXECUTE IMMEDIATE 'DELETE FROM departments WHERE ' || v_column || ' = :num'

USING dept_id;

EXECUTE IMMEDIATE 'ALTER SESSION SET SQL_TRACE TRUE';

EXECUTE IMMEDIATE 'DROP TABLE bonus';

END;

Example 7–2 , a standalone procedure accepts the name of a database table and an

optional

WHERE

-clause condition. If you omit the condition, the procedure deletes all rows from the table. Otherwise, the procedure deletes only those rows that meet the condition.

Example 7–2 Dynamic SQL Procedure that Accepts Table Name and WHERE Clause

CREATE TABLE employees_temp AS SELECT * FROM employees;

CREATE OR REPLACE PROCEDURE delete_rows (

table_name IN VARCHAR2,

condition IN VARCHAR2 DEFAULT NULL) AS

where_clause VARCHAR2(100) := ' WHERE ' || condition;

v_table VARCHAR2(30);

BEGIN

-- first make sure that the table actually exists; if not, raise an exception

SELECT OBJECT_NAME INTO v_table FROM USER_OBJECTS

WHERE OBJECT_NAME = UPPER(table_name) AND OBJECT_TYPE = 'TABLE';

IF condition IS NULL THEN where_clause := NULL; END IF;

EXECUTE IMMEDIATE 'DELETE FROM ' || v_table || where_clause;

EXCEPTION

WHEN NO_DATA_FOUND THEN

DBMS_OUTPUT.PUT_LINE ('Invalid table: ' || table_name);

END;

BEGIN

delete_rows('employees_temp', 'employee_id = 111');

END;

Specifying Parameter Modes for Bind Variables in Dynamic SQL Strings

With the

USING

clause, the mode defaults to

, so you do not need to specify a parameter mode for input bind arguments.

With the

RETURNING INTO

clause, the mode is

OUT

, so you cannot specify a parameter mode for output bind arguments.

You must specify the parameter mode in more complicated cases, such as this one where you call a procedure from a dynamic PL/SQL block:

CREATE PROCEDURE create_dept (

deptid IN OUT NUMBER,

dname IN VARCHAR2,

mgrid IN NUMBER,

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Using Bulk Dynamic SQL in PL/SQL

locid IN NUMBER) AS

BEGIN

SELECT departments_seq.NEXTVAL INTO deptid FROM dual;

INSERT INTO departments VALUES (deptid, dname, mgrid, locid);

END;

To call the procedure from a dynamic PL/SQL block, you must specify the

IN OUT mode for the bind argument associated with formal parameter deptid

, as shown in

Example 7–3

Example 7–3 Using IN OUT Bind Arguments to Specify Substitutions

DECLARE

plsql_block VARCHAR2(500);

new_deptid NUMBER(4);

new_dname VARCHAR2(30) := 'Advertising';

new_mgrid NUMBER(6) := 200;

new_locid NUMBER(4) := 1700;

BEGIN

plsql_block := 'BEGIN create_dept(:a, :b, :c, :d); END;';

EXECUTE IMMEDIATE plsql_block

USING IN OUT new_deptid, new_dname, new_mgrid, new_locid;

END;

Using Bulk Dynamic SQL in PL/SQL

Bulk SQL passes entire collections back and forth, not just individual elements. This technique improves performance by minimizing the number of context switches between the PL/SQL and SQL engines. You can use a single statement instead of a loop that issues a SQL statement in every iteration.

Using the following commands, clauses, and cursor attribute, your applications can construct bulk SQL statements, then execute them dynamically at run time:

BULK FETCH

statement

BULK EXECUTE IMMEDIATE

statement

FORALL

statement

COLLECT INTO

clause

RETURNING INTO

clause

%BULK_ROWCOUNT

cursor attribute

The static versions of these statements, clauses, and cursor attribute are discussed in

"Reducing Loop Overhead for DML Statements and Queries with Bulk SQL" on page 11-8. Refer to that section for background information.

Using Dynamic SQL with Bulk SQL

Bulk binding lets Oracle bind a variable in a SQL statement to a collection of values.

The collection type can be any PL/SQL collection type: index-by table, nested table, or varray. The collection elements must have a SQL datatype such as

CHAR

DATE

, or

NUMBER

. Three statements support dynamic bulk binds:

EXECUTE IMMEDIATE

FETCH

, and

FORALL

Performing SQL Operations with Native Dynamic SQL

7-5

Using Bulk Dynamic SQL in PL/SQL

EXECUTE IMMEDIATE

You can use the

BULK COLLECT INTO

clause with the

EXECUTE IMMEDIATE statement to store values from each column of a query's result set in a separate collection.

You can use the

RETURNING BULK COLLECT INTO

clause with the

EXECUTE

IMMEDIATE

statement to store the results of an

INSERT

UPDATE

, or

DELETE statement in a set of collections.

FETCH

You can use the

BULK COLLECT INTO

clause with the

FETCH

statement to store values from each column of a cursor in a separate collection.

FORALL

You can put an

EXECUTE IMMEDIATE

statement with the

RETURNING BULK

COLLECT INTO

inside a

FORALL

statement. You can store the results of all the

INSERT

UPDATE

, or

DELETE

statements in a set of collections.

You can pass subscripted collection elements to the

EXECUTE IMMEDIATE

statement through the

USING

clause. You cannot concatenate the subscripted elements directly into the string argument to

EXECUTE IMMEDIATE

; for example, you cannot build a collection of table names and write a

FORALL

statement where each iteration applies to a different table.

Examples of Dynamic Bulk Binds

This sections contains examples of dynamic bulk binds.You can bind define variables in a dynamic query using the

BULK COLLECT INTO

clause. As shown in Example 7–4 ,

you can use that clause in a bulk

FETCH

or bulk

EXECUTE IMMEDIATE

statement.

Example 7–4 Dynamic SQL with BULK COLLECT INTO Clause

DECLARE

TYPE EmpCurTyp IS REF CURSOR;

TYPE NumList IS TABLE OF NUMBER;

TYPE NameList IS TABLE OF VARCHAR2(25);

emp_cv EmpCurTyp;

empids NumList;

enames NameList;

sals NumList;

BEGIN

OPEN emp_cv FOR 'SELECT employee_id, last_name FROM employees';

FETCH emp_cv BULK COLLECT INTO empids, enames;

CLOSE emp_cv;

EXECUTE IMMEDIATE 'SELECT salary FROM employees'

BULK COLLECT INTO sals;

END;

Only

INSERT

UPDATE

, and

DELETE

statements can have output bind variables. You bulk-bind them with the

RETURNING BULK COLLECT INTO

clause of

EXECUTE

IMMEDIATE

, as shown in

Example 7–5

Example 7–5 Dynamic SQL with RETURNING BULK COLLECT INTO Clause

DECLARE

TYPE NameList IS TABLE OF VARCHAR2(15);

enames NameList;

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Guidelines for Using Dynamic SQL with PL/SQL

bonus_amt NUMBER := 50;

sql_stmt VARCHAR(200);

BEGIN

sql_stmt := 'UPDATE employees SET salary = salary + :1

RETURNING last_name INTO :2';

EXECUTE IMMEDIATE sql_stmt

USING bonus_amt RETURNING BULK COLLECT INTO enames;

END;

To bind the input variables in a SQL statement, you can use the

FORALL

statement and

USING

clause, as shown in

Example 7–6

. The SQL statement cannot be a query.

Example 7–6 Dynamic SQL Inside FORALL Statement

DECLARE

TYPE NumList IS TABLE OF NUMBER;

TYPE NameList IS TABLE OF VARCHAR2(15);

empids NumList;

enames NameList;

BEGIN

empids := NumList(101,102,103,104,105);

FORALL i IN 1..5

EXECUTE IMMEDIATE

'UPDATE employees SET salary = salary * 1.04 WHERE employee_id = :1

RETURNING last_name INTO :2'

USING empids(i) RETURNING BULK COLLECT INTO enames;

END;

Guidelines for Using Dynamic SQL with PL/SQL

This section shows you how to take full advantage of dynamic SQL and how to avoid some common pitfalls.

Note:

When using dynamic SQL with PL/SQL, be aware of the risks of SQL injection, which is a possible security issue. For more information on SQL injection and possible problems, see Oracle

Database Application Developer's Guide - Fundamentals. You can also search for "SQL injection" on the Oracle Technology Network at http://www.oracle.com/technology/

Building a Dynamic Query with Dynamic SQL

You use three statements to process a dynamic multi-row query:

OPEN-FOR

FETCH

, and

. First, you

OPEN

a cursor variable

FOR

a multi-row query. Then, you

FETCH rows from the result set one at a time. When all the rows are processed, you

the cursor variable. For more information about cursor variables, see

"Using Cursor

Variables (REF CURSORs)" on page 6-20.

When to Use or Omit the Semicolon with Dynamic SQL

When building up a single SQL statement in a string, do not include any semicolon at the end.

Performing SQL Operations with Native Dynamic SQL

7-7

Guidelines for Using Dynamic SQL with PL/SQL

When building up a PL/SQL anonymous block, include the semicolon at the end of each PL/SQL statement and at the end of the anonymous block. For example:

BEGIN

EXECUTE IMMEDIATE 'BEGIN DBMS_OUTPUT.PUT_LINE(''semicolons''); END;';

END;

Improving Performance of Dynamic SQL with Bind Variables

When you code

INSERT

UPDATE

DELETE

, and

SELECT

statements directly in

PL/SQL, PL/SQL turns the variables into bind variables automatically, to make the statements work efficiently with SQL. When you build up such statements in dynamic

SQL, you need to specify the bind variables yourself to get the same performance.

In the following example, Oracle opens a different cursor for each distinct value of emp_id

. This can lead to resource contention and poor performance as each statement is parsed and cached.

CREATE PROCEDURE fire_employee (emp_id NUMBER) AS

BEGIN

EXECUTE IMMEDIATE

'DELETE FROM employees WHERE employee_id = ' || TO_CHAR(emp_id);

END;

You can improve performance by using a bind variable, which allows Oracle to reuse the same cursor for different values of emp_id

CREATE PROCEDURE fire_employee (emp_id NUMBER) AS

BEGIN

EXECUTE IMMEDIATE

'DELETE FROM employees WHERE employee_id = :id' USING emp_id;

END;

Passing Schema Object Names As Parameters

Suppose you need a procedure that accepts the name of any database table, then drops that table from your schema. You must build a string with a statement that includes the object names, then use

EXECUTE IMMEDIATE

to execute the statement:

CREATE TABLE employees_temp AS SELECT last_name FROM employees;

CREATE PROCEDURE drop_table (table_name IN VARCHAR2) AS

BEGIN

EXECUTE IMMEDIATE 'DROP TABLE ' || table_name;

END;

Use concatenation to build the string, rather than trying to pass the table name as a bind variable through the

USING

clause.

In addition, if you need to call a procedure whose name is unknown until runtime, you can pass a parameter identifying the procedure. For example, the following procedure can call another procedure ( drop_table

) by specifying the procedure name when executed.

CREATE PROCEDURE run_proc (proc_name IN VARCHAR2, table_name IN VARCHAR2) AS

BEGIN

EXECUTE IMMEDIATE 'CALL "' || proc_name || '" ( :proc_name )' using table_name;

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END;

If you want to drop a table with the drop_table

procedure, you can run the procedure as follows. Note that the procedure name is capitalized.

CREATE TABLE employees_temp AS SELECT last_name FROM employees;

BEGIN

run_proc('DROP_TABLE', 'employees_temp');

END;

Using Duplicate Placeholders with Dynamic SQL

Placeholders in a dynamic SQL statement are associated with bind arguments in the

USING

clause by position, not by name. If you specify a sequence of placeholders like

:a, :a, :b, :b

, you must include four items in the

USING

clause. For example, given the dynamic string sql_stmt := 'INSERT INTO payroll VALUES (:x, :x, :y, :x)'; the fact that the name X is repeated is not significant. You can code the corresponding

USING

clause with four different bind variables:

EXECUTE IMMEDIATE sql_stmt USING a, a, b, a;

If the dynamic statement represents a PL/SQL block, the rules for duplicate placeholders are different. Each unique placeholder maps to a single item in the

USING clause. If the same placeholder appears two or more times, all references to that name correspond to one bind argument in the

USING

clause. In

Example 7–7 , all references

to the placeholder x

are associated with the first bind argument a, and the second unique placeholder y

is associated with the second bind argument b.

Example 7–7 Using Duplicate Placeholders With Dynamic SQL

CREATE PROCEDURE calc_stats(w NUMBER, x NUMBER, y NUMBER, z NUMBER) IS

BEGIN

DBMS_OUTPUT.PUT_LINE(w + x + y + z);

END;

DECLARE

a NUMBER := 4;

b NUMBER := 7;

plsql_block VARCHAR2(100);

BEGIN

plsql_block := 'BEGIN calc_stats(:x, :x, :y, :x); END;';

EXECUTE IMMEDIATE plsql_block USING a, b;

END;

Using Cursor Attributes with Dynamic SQL

The SQL cursor attributes

%FOUND

%ISOPEN

%NOTFOUND

, and

%ROWCOUNT

work when you issue an

INSERT

UPDATE

DELETE

, or single-row

SELECT

statement in dynamic SQL:

BEGIN

EXECUTE IMMEDIATE 'DELETE FROM employees WHERE employee_id > 1000';

DBMS_OUTPUT.PUT_LINE('Number of employees deleted: ' || TO_CHAR(SQL%ROWCOUNT));

Performing SQL Operations with Native Dynamic SQL

7-9

Guidelines for Using Dynamic SQL with PL/SQL

END;

Likewise, when appended to a cursor variable name, the cursor attributes return information about the execution of a multi-row query:

Example 7–8 Accessing %ROWCOUNT For an Explicit Cursor

DECLARE

TYPE cursor_ref IS REF CURSOR;

c1 cursor_ref;

TYPE emp_tab IS TABLE OF employees%ROWTYPE;

rec_tab emp_tab;

rows_fetched NUMBER;

BEGIN

OPEN c1 FOR 'SELECT * FROM employees';

FETCH c1 BULK COLLECT INTO rec_tab;

rows_fetched := c1%ROWCOUNT;

DBMS_OUTPUT.PUT_LINE('Number of employees fetched: ' || TO_CHAR(rows_fetched));

END;

For more information about cursor attributes, see

"Managing Cursors in PL/SQL" on page 6-6.

Passing Nulls to Dynamic SQL

The literal

NULL

is not allowed in the

USING

clause. To work around this restriction, replace the keyword

NULL

with an uninitialized variable:

CREATE TABLE employees_temp AS SELECT * FROM EMPLOYEES;

DECLARE

a_null CHAR(1); -- set to NULL automatically at run time

BEGIN

EXECUTE IMMEDIATE 'UPDATE employees_temp SET commission_pct = :x' USING a_null;

END;

Using Database Links with Dynamic SQL

PL/SQL subprograms can execute dynamic SQL statements that use database links to refer to objects on remote databases:

CREATE PROCEDURE delete_dept (db_link VARCHAR2, dept_id INTEGER) IS

BEGIN

EXECUTE IMMEDIATE 'DELETE FROM departments@' || db_link ||

' WHERE department_id = :num' USING dept_id;

END;

-- delete department id 41 in the departments table on the remote DB hr_db

CALL delete_dept('hr_db', 41);

The targets of remote procedure calls (RPCs) can contain dynamic SQL statements. For example, suppose the following standalone function, which returns the number of rows in a table, resides on the hr_db

database in London:

CREATE FUNCTION row_count (tab_name VARCHAR2) RETURN NUMBER AS

rows NUMBER;

BEGIN

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Guidelines for Using Dynamic SQL with PL/SQL

EXECUTE IMMEDIATE 'SELECT COUNT(*) FROM ' || tab_name INTO rows;

RETURN rows;

END;

-- From an anonymous block, you might call the function remotely, as follows:

DECLARE

emp_count INTEGER;

BEGIN

emp_count := row_count@hr_db('employees');

DBMS_OUTPUT.PUT_LINE(emp_count);

END;

Using Invoker Rights with Dynamic SQL

Dynamic SQL lets you write schema-management procedures that can be centralized in one schema, and can be called from other schemas and operate on the objects in those schemas. For example, this procedure can drop any kind of database object:

CREATE OR REPLACE PROCEDURE drop_it (kind IN VARCHAR2, name IN VARCHAR2)

AUTHID CURRENT_USER AS

BEGIN

EXECUTE IMMEDIATE 'DROP ' || kind || ' ' || name;

END;

Let's say that this procedure is part of the

schema. Without the

AUTHID

clause, the procedure would always drop objects in the

schema, regardless of who calls it.

Even if you pass a fully qualified object name, this procedure would not have the privileges to make changes in other schemas.

The

AUTHID

clause lifts both of these restrictions. It lets the procedure run with the privileges of the user that invokes it, and makes unqualified references refer to objects in that user's schema.

For details, see

"Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)" on page 8-15.

Using Pragma RESTRICT_REFERENCES with Dynamic SQL

A function called from SQL statements must obey certain rules meant to control side effects. (See

"Controlling Side Effects of PL/SQL Subprograms" on page 8-23.) To check

for violations of the rules, you can use the pragma

RESTRICT_REFERENCES

. The pragma asserts that a function does not read or write database tables or package variables. (For more information, See Oracle Database Application Developer's Guide -

Fundamentals.)

If the function body contains a dynamic

INSERT

UPDATE

, or

DELETE

statement, the function always violates the rules write no database state

(

WNDS

) and read no database state

(

RNDS

). PL/SQL cannot detect those side-effects automatically, because dynamic SQL statements are checked at run time, not at compile time. In an

EXECUTE IMMEDIATE

statement, only the

INTO

clause can be checked at compile time for violations of

RNDS

Avoiding Deadlocks with Dynamic SQL

In a few situations, executing a SQL data definition statement results in a deadlock.

For example, the following procedure causes a deadlock because it attempts to drop

Performing SQL Operations with Native Dynamic SQL

7-11

Guidelines for Using Dynamic SQL with PL/SQL itself. To avoid deadlocks, never try to

ALTER

DROP

a subprogram or package while you are still using it.

CREATE OR REPLACE PROCEDURE calc_bonus (emp_id NUMBER) AS

BEGIN

EXECUTE IMMEDIATE 'DROP PROCEDURE calc_bonus'; -- deadlock!

END;

Backward Compatibility of the USING Clause

When a dynamic

INSERT

UPDATE

, or

DELETE

statement has a

RETURNING

clause, output bind arguments can go in the

RETURNING INTO

clause or the

USING

clause. In new applications, use the

RETURNING INTO

clause. In old applications, you can continue to use the

USING

clause.

Using Dynamic SQL With PL/SQL Records and Collections

You can use dynamic SQL with records and collections. As shown in Example 7–9 , you

can fetch rows from the result set of a dynamic multi-row query into a record:

Example 7–9 Dynamic SQL Fetching into a Record

DECLARE

TYPE EmpCurTyp IS REF CURSOR;

emp_cv EmpCurTyp;

emp_rec employees%ROWTYPE;

sql_stmt VARCHAR2(200);

v_job VARCHAR2(10) := 'ST_CLERK';

BEGIN

sql_stmt := 'SELECT * FROM employees WHERE job_id = :j';

OPEN emp_cv FOR sql_stmt USING v_job;

LOOP

FETCH emp_cv INTO emp_rec;

EXIT WHEN emp_cv%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('Name: ' || emp_rec.last_name || ' Job Id: ' ||

emp_rec.job_id);

END LOOP;

CLOSE emp_cv;

END;

For an example of using dynamic SQL with object types, see "Using Dynamic SQL

With Objects" on page 12-11.

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Oracle Database PL/SQL User’s Guide and Reference

Using PL/SQL Subprograms

This chapter shows you how to turn sets of statements into reusable subprograms.

Subprograms are like building blocks for modular, maintainable applications.

This chapter contains these topics:

■

What Are Subprograms?

■

Advantages of PL/SQL Subprograms

Understanding PL/SQL Procedures

Understanding PL/SQL Functions

Declaring Nested PL/SQL Subprograms

■

Passing Parameters to PL/SQL Subprograms

Overloading Subprogram Names

How Subprogram Calls Are Resolved

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

Using Recursion with PL/SQL

Calling External Subprograms

Controlling Side Effects of PL/SQL Subprograms

Understanding Subprogram Parameter Aliasing

What Are Subprograms?

Subprograms are named PL/SQL blocks that can be called with a set of parameters.

PL/SQL has two types of subprograms, procedures and functions. Generally, you use a procedure to perform an action and a function to compute a value.

Similar to anonymous blocks, subprograms have:

■

A declarative part, with declarations of types, cursors, constants, variables, exceptions, and nested subprograms. These items are local and cease to exist when the subprogram ends.

■

An executable part, with statements that assign values, control execution, and manipulate Oracle data.

An optional exception-handling part, which deals with runtime error conditions.

Example 8–1

shows a string-manipulation procedure double

that accepts both input and output parameters, and handles potential errors.

Using PL/SQL Subprograms

8-1

Advantages of PL/SQL Subprograms

Example 8–1 Simple PL/SQL Procedure

DECLARE

in_string VARCHAR2(100) := 'This is my test string.';

out_string VARCHAR2(200);

PROCEDURE double ( original IN VARCHAR2, new_string OUT VARCHAR2 ) AS

BEGIN

new_string := original || ' + ' || original;

EXCEPTION

WHEN VALUE_ERROR THEN

DBMS_OUTPUT.PUT_LINE('Output buffer not long enough.');

END;

BEGIN

double(in_string, out_string);

DBMS_OUTPUT.PUT_LINE(in_string || ' - ' || out_string);

END;

Example 8–2

shows a numeric function square

that declares a local variable to hold temporary results, and returns a value when finished.

Example 8–2 Simple PL/SQL Function

DECLARE

FUNCTION square(original NUMBER)

RETURN NUMBER AS original_squared NUMBER;

BEGIN

original_squared := original * original;

RETURN original_squared;

END;

BEGIN

DBMS_OUTPUT.PUT_LINE(square(100));

END;

Note:

■

The SQL

CREATE FUNCTION

statement lets you create standalone functions that are stored in an Oracle database. For information, see

CREATE FUNCTION

in Oracle Database SQL Reference.

The SQL

CREATE PROCEDURE

statement lets you create standalone procedures that are stored in the database. For information, see

CREATE PROCEDURE

in Oracle Database SQL

Reference.

You can execute the

CREATE FUNCTION

CREATE PROCEDURE statement interactively from SQL*Plus, or from a program using native dynamic SQL. See

Chapter 7, "Performing SQL Operations with Native Dynamic SQL" .

Advantages of PL/SQL Subprograms

Subprograms let you extend the PL/SQL language. Procedures act like new statements. Functions act like new expressions and operators.

Subprograms let you break a program down into manageable, well-defined modules.

You can use top-down design and the stepwise refinement approach to problem solving.

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Understanding PL/SQL Procedures

Subprograms promote reusability. Once tested, a subprogram can be reused in any number of applications. You can call PL/SQL subprograms from many different environments, so that you do not have to reinvent the wheel each time you use a new language or API to access the database.

Subprograms promote maintainability. You can change the internals of a subprogram without changing other subprograms that call it. Subprograms play a big part in other maintainability features, such as packages and object types.

Dummy subprograms (stubs) let you defer the definition of procedures and functions until after testing the main program. You can design applications from the top down, thinking abstractly, without worrying about implementation details.

When you use PL/SQL subprograms to define an API, you can make your code even more reusable and maintainable by grouping the subprograms into a PL/SQL package. For more information about packages, see

Chapter 9, "Using PL/SQL

Packages"

Understanding PL/SQL Procedures

A procedure is a subprogram that performs a specific action. You specify the name of the procedure, its parameters, its local variables, and the

BEGIN-END

block that contains its code and handles any exceptions. For information on the syntax of the

PROCEDURE

declaration, see "Procedure Declaration" on page 13-90.

For each parameter, you specify:

■

Its name.

■

Its parameter mode (

OUT

, or

IN OUT

). If you omit the mode, the default is

The optional

NOCOPY

keyword speeds up processing of large

OUT

IN OUT parameters.

■

Its datatype. You specify only the type, not any length or precision constraints.

Optionally, its default value.

You can specify whether the procedure executes using the schema and permissions of

the user who defined it, or the user who calls it. For more information, see "Using

Invoker's Rights Versus Definer's Rights (AUTHID Clause)" on page 8-15.

You can specify whether it should be part of the current transaction, or execute in its own transaction where it can

COMMIT

ROLLBACK

without ending the transaction of

the caller. For more information, see "Doing Independent Units of Work with

Autonomous Transactions" on page 6-37.

A procedure has two parts: the specification (spec for short) and the body. The procedure spec begins with the keyword

PROCEDURE

and ends with the procedure name or a parameter list, followed by the reserved word

(or

). Parameter declarations are optional. Procedures that take no parameters are written without parentheses.

The procedure body begins with the reserved word

(or

) and ends with the keyword

END

followed by an optional procedure name. The procedure body has three parts: a declarative part, an executable part, and an optional exception-handling part.

The declarative part contains local declarations. The keyword

DECLARE

is used for anonymous PL/SQL blocks, but not procedures. The executable part contains statements, which are placed between the keywords

BEGIN

and

EXCEPTION

(or

END

At least one statement must appear in the executable part of a procedure. You can use the

NULL

statement to define a placeholder procedure or specify that the procedure

Using PL/SQL Subprograms

8-3

Understanding PL/SQL Functions does nothing. The exception-handling part contains exception handlers, which are placed between the keywords

EXCEPTION

and

END

A procedure is called as a PL/SQL statement. For example, you might call the procedure raise_salary

as follows: raise_salary(emp_id, amount);

Understanding PL/SQL Functions

A function is a subprogram that computes a value. Functions and procedures are structured alike, except that functions have a

RETURN

clause. Functions have a number of optional keywords, used to declare a special class of functions known as table functions. They are typically used for transforming large amounts of data in data warehousing applications. For information on the syntax of the

FUNCTION

declaration,

see "Function Declaration" on page 13-59.

The

AUTHID

clause determines whether a stored function executes with the privileges of its owner (the default) or current user and whether its unqualified references to schema objects are resolved in the schema of the owner or current user. You can override the default behavior by specifying

CURRENT_USER

The

PARALLEL_ENABLE

option declares that a stored function can be used safely in the slave sessions of parallel DML evaluations. The state of a main (logon) session is never shared with slave sessions. Each slave session has its own state, which is initialized when the session begins. The function result should not depend on the state of session ( static

) variables. Otherwise, results might vary across sessions.

The

DETERMINISTIC

option helps the optimizer avoid redundant function calls. If a stored function was called previously with the same arguments, the optimizer can elect to use the previous result. For more information and possible limitations of the

DETERMINISTIC

option, see

CREATE FUNCTION

in Oracle Database SQL Reference.

The pragma

AUTONOMOUS_TRANSACTION

instructs the PL/SQL compiler to mark a function as autonomous (independent). Autonomous transactions let you suspend the main transaction, do SQL operations, commit or roll back those operations, then resume the main transaction.

You cannot constrain (with

NOT NULL

for example) the datatype of a parameter or a function return value. However, you can use a workaround to size-constrain them indirectly. See

"Understanding PL/SQL Procedures" on page 8-3.

Like a procedure, a function has two parts: the spec and the body. The function spec begins with the keyword

FUNCTION

and ends with the

RETURN

clause, which specifies the datatype of the return value. Parameter declarations are optional. Functions that take no parameters are written without parentheses.

The function body begins with the keyword

(or

) and ends with the keyword

END

followed by an optional function name. The function body has three parts: a declarative part, an executable part, and an optional exception-handling part.

The declarative part contains local declarations, which are placed between the keywords

and

BEGIN

. The keyword

DECLARE

is not used. The executable part contains statements, which are placed between the keywords

BEGIN

and

EXCEPTION

(or

END

). One or more

RETURN

statements must appear in the executable part of a function. The exception-handling part contains exception handlers, which are placed between the keywords

EXCEPTION

and

END

A function is called as part of an expression. For example:

IF sal_ok(new_sal, new_title) THEN ...

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Declaring Nested PL/SQL Subprograms

Using the RETURN Statement

The

RETURN

statement immediately ends the execution of a subprogram and returns control to the caller. Execution continues with the statement following the subprogram call. (Do not confuse the

RETURN

statement with the

RETURN

clause in a function spec, which specifies the datatype of the return value.)

A subprogram can contain several

RETURN

statements. The subprogram does not have to conclude with a

RETURN

statement. Executing any

RETURN

statement completes the subprogram immediately.

In procedures, a

RETURN

statement does not return a value and so cannot contain an expression. The statement returns control to the caller before the end of the procedure.

In functions, a

RETURN

statement must contain an expression, which is evaluated when the

RETURN

statement is executed. The resulting value is assigned to the function identifier, which acts like a variable of the type specified in the

RETURN clause. See the use of the

RETURN

statement in

Example 8–2 on page 8-2.

The expression in a function

RETURN

statement can be arbitrarily complex:

CREATE OR REPLACE FUNCTION half_of_square(original NUMBER)

RETURN NUMBER IS

BEGIN

RETURN (original * original)/2 + (original * 4);

END half_of_square;

In a function, there must be at least one execution path that leads to a

RETURN statement. Otherwise, you get a function returned without value

error at run time.

Declaring Nested PL/SQL Subprograms

You can declare subprograms in any PL/SQL block, subprogram, or package. The subprograms must go at the end of the declarative section, after all other items.

You must declare a subprogram before calling it. This requirement can make it difficult to declare several nested subprograms that call each other.

You can declare interrelated nested subprograms using a forward declaration: a subprogram spec terminated by a semicolon, with no body.

Although the formal parameter list appears in the forward declaration, it must also appear in the subprogram body. You can place the subprogram body anywhere after the forward declaration, but they must appear in the same program unit.

Example 8–3 Forward Declaration for a Nested Subprogram

DECLARE

PROCEDURE proc1(number1 NUMBER); -- forward declaration

PROCEDURE proc2(number2 NUMBER) IS

BEGIN

proc1(number2); -- calls proc1

END;

PROCEDURE proc1(number1 NUMBER) IS

BEGIN

proc2 (number1); -- calls proc2

END;

BEGIN

NULL;

Using PL/SQL Subprograms

8-5

Passing Parameters to PL/SQL Subprograms

END;

Passing Parameters to PL/SQL Subprograms

This section explains how to pass information in and out of PL/SQL subprograms using parameters:

■

Actual Versus Formal Subprogram Parameters

Using Positional, Named, or Mixed Notation for Subprogram Parameters

Specifying Subprogram Parameter Modes

Using Default Values for Subprogram Parameters

Actual Versus Formal Subprogram Parameters

Subprograms pass information using parameters:

■

The variables declared in a subprogram specification and referenced in the subprogram body are formal parameters.

The variables or expressions passed from the calling subprogram are actual parameters.

A good programming practice is to use different names for actual and formal parameters.

When you call a procedure, the actual parameters are evaluated and the results are assigned to the corresponding formal parameters. If necessary, before assigning the value of an actual parameter to a formal parameter, PL/SQL converts the datatype of the value. For example, if you pass a number when the procedure expects a string,

PL/SQL converts the parameter so that the procedure receives a string.

The actual parameter and its corresponding formal parameter must have compatible datatypes. For instance, PL/SQL cannot convert between the

DATE

and

NUMBER datatypes, or convert a string to a number if the string contains extra characters such as dollar signs.

The procedure in Example 8–4

declares two formal parameters named emp_id

and amount

and the procedure call specifies actual parameters emp_num

and bonus

Example 8–4 Formal Parameters and Actual Parameters

DECLARE

emp_num NUMBER(6) := 120;

bonus NUMBER(6) := 100;

merit NUMBER(4) := 50;

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER) IS

BEGIN

UPDATE employees SET salary = salary + amount WHERE employee_id = emp_id;

END raise_salary;

BEGIN

raise_salary(emp_num, bonus); -- procedure call specifies actual parameters

raise_salary(emp_num, merit + bonus); -- expressions can be used as parameters

END;

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Passing Parameters to PL/SQL Subprograms

Using Positional, Named, or Mixed Notation for Subprogram Parameters

When calling a subprogram, you can write the actual parameters using either:

■

Positional notation. You specify the same parameters in the same order as they are declared in the procedure.

This notation is compact, but if you specify the parameters (especially literals) in the wrong order, the bug can be hard to detect. You must change your code if the procedure's parameter list changes.

Named notation. You specify the name of each parameter along with its value. An arrow (

) serves as the association operator. The order of the parameters is not significant.

This notation is more verbose, but makes your code easier to read and maintain.

You can sometimes avoid changing your code if the procedure's parameter list changes, for example if the parameters are reordered or a new optional parameter is added. Named notation is a good practice to use for any code that calls someone else's API, or defines an API for someone else to use.

■

Mixed notation. You specify the first parameters with positional notation, then switch to named notation for the last parameters.

You can use this notation to call procedures that have some required parameters, followed by some optional parameters.

Example 8–5

shows equivalent procedure calls using positional, named, and mixed notation.

Example 8–5 Subprogram Calls Using Positional, Named, and Mixed Notation

DECLARE

emp_num NUMBER(6) := 120;

bonus NUMBER(6) := 50;

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER) IS

BEGIN

UPDATE employees SET salary = salary + amount WHERE employee_id = emp_id;

END raise_salary;

BEGIN

raise_salary(emp_num, bonus); -- positional procedure call for actual parameters

raise_salary(amount => bonus, emp_id => emp_num); -- named parameters

raise_salary(emp_num, amount => bonus); -- mixed parameters

END;

Specifying Subprogram Parameter Modes

You use parameter modes to define the behavior of formal parameters. The three parameter modes are

(the default),

OUT

, and

IN OUT

Any parameter mode can be used with any subprogram. Avoid using the

OUT

and

OUT

modes with functions. To have a function return multiple values is a poor programming practice. Also, functions should be free from side effects, which change the values of variables not local to the subprogram.

Using the IN Mode

parameter lets you pass values to the subprogram being called. Inside the subprogram, an

parameter acts like a constant. It cannot be assigned a value.

Using PL/SQL Subprograms

8-7

Passing Parameters to PL/SQL Subprograms

You can pass a constant, literal, initialized variable, or expression as an IN parameter.

parameters can be initialized to default values, which are used if those parameters

are omitted from the subprogram call. For more information, see "Using Default

Values for Subprogram Parameters" on page 8-9.

Using the OUT Mode

OUT

parameter returns a value to the caller of a subprogram. Inside the subprogram, an

OUT

parameter acts like a variable. You can change its value, and reference the value after assigning it:

Example 8–6 Using the OUT Mode

DECLARE

emp_num NUMBER(6) := 120;

bonus NUMBER(6) := 50;

emp_last_name VARCHAR2(25);

PROCEDURE raise_salary (emp_id IN NUMBER, amount IN NUMBER,

emp_name OUT VARCHAR2) IS

BEGIN

UPDATE employees SET salary = salary + amount WHERE employee_id = emp_id;

SELECT last_name INTO emp_name FROM employees WHERE employee_id = emp_id;

END raise_salary;

BEGIN

raise_salary(emp_num, bonus, emp_last_name);

DBMS_OUTPUT.PUT_LINE('Salary has been updated for: ' || emp_last_name);

END;

You must pass a variable, not a constant or an expression, to an

OUT

parameter. Its previous value is lost unless you specify the

NOCOPY

keyword or the subprogram exits with an unhandled exception. See

"Using Default Values for Subprogram Parameters" on page 8-9.

Like variables,

OUT

formal parameters are initialized to

NULL

. The datatype of an

OUT formal parameter cannot be a subtype defined as

NOT NULL

, such as the built-in subtypes

NATURALN

and

POSITIVEN

. Otherwise, when you call the subprogram,

PL/SQL raises

VALUE_ERROR

Before exiting a subprogram, assign values to all

OUT

formal parameters. Otherwise, the corresponding actual parameters will be null. If you exit successfully, PL/SQL assigns values to the actual parameters. If you exit with an unhandled exception,

PL/SQL does not assign values to the actual parameters.

Using the IN OUT Mode

IN OUT

parameter passes initial values to a subprogram and returns updated values to the caller. It can be assigned a value and its value can be read. Typically, an

IN OUT

parameter is a string buffer or numeric accumulator, that is read inside the subprogram and then updated.

The actual parameter that corresponds to an

IN OUT

formal parameter must be a variable; it cannot be a constant or an expression.

If you exit a subprogram successfully, PL/SQL assigns values to the actual parameters.

If you exit with an unhandled exception, PL/SQL does not assign values to the actual parameters.

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Passing Parameters to PL/SQL Subprograms

Summary of Subprogram Parameter Modes

Table 8–1

summarizes all you need to know about the parameter modes.

Table 8–1 Parameter Modes

IN OUT IN OUT

The default

Passes values to a subprogram

Must be specified Must be specified

Returns values to the caller Passes initial values to a subprogram and returns updated values to the caller

Formal parameter acts like an uninitialized variable

Formal parameter acts like an initialized variable

Formal parameter acts like a constant

Formal parameter cannot be assigned a value

Formal parameter must be assigned a value

Actual parameter can be a constant, initialized variable, literal, or expression

Actual parameter must be a variable

Formal parameter should be assigned a value

Actual parameter must be a variable

Actual parameter is passed by reference (a pointer to the value is passed in)

Actual parameter is passed by value (a copy of the value is passed out) unless

NOCOPY

is specified

Actual parameter is passed by value (a copy of the value is passed in and out) unless

NOCOPY

is specified

Using Default Values for Subprogram Parameters

By initializing

parameters to default values, you can pass different numbers of actual parameters to a subprogram, accepting the default values for any parameters you omit. You can also add new formal parameters without having to change every call to the subprogram.

If a parameter is omitted, the default value of its corresponding formal parameter is used. You cannot skip a formal parameter by leaving out its actual parameter. To omit the first parameter and specify the second, use named notation.

You cannot assign a null to an uninitialized formal parameter by leaving out its actual parameter. You must pass the null explicitly, or you can specify a default value of

NULL

in the declaration.

Example 8–7

illustrates the use of default values for subprogram parameters.

Example 8–7 Procedure with Default Parameter Values

DECLARE

emp_num NUMBER(6) := 120;

bonus NUMBER(6);

merit NUMBER(4);

PROCEDURE raise_salary (emp_id IN NUMBER, amount IN NUMBER DEFAULT 100,

extra IN NUMBER DEFAULT 50) IS

BEGIN

UPDATE employees SET salary = salary + amount + extra

WHERE employee_id = emp_id;

END raise_salary;

BEGIN

raise_salary(120); -- same as raise_salary(120, 100, 50)

raise_salary(emp_num, extra => 25); -- same as raise_salary(120, 100, 25)

END;

Using PL/SQL Subprograms

8-9

Overloading Subprogram Names

PL/SQL lets you overload subprogram names and type methods. You can use the same name for several different subprograms as long as their formal parameters differ in number, order, or datatype family. For an example of an overloaded procedure in a package, see

Example 9–3 on page 9-6.

Example 8–8

shows how you can define two subprograms with the same name. The procedures initialize different types of collections. Because the processing in these two procedures is the same, it is logical to give them the same name.

You can place the two overloaded initialize

procedures in the same block, subprogram, package, or object type. PL/SQL determines which procedure to call by checking their formal parameters. The version of initialize

that PL/SQL uses depends on whether you call the procedure with a

DateTabTyp

NumTabTyp parameter.

Example 8–8 Overloading a Subprogram Name

DECLARE

TYPE DateTabTyp IS TABLE OF DATE INDEX BY PLS_INTEGER;

TYPE NumTabTyp IS TABLE OF NUMBER INDEX BY PLS_INTEGER;

hiredate_tab DateTabTyp;

sal_tab NumTabTyp;

PROCEDURE initialize (tab OUT DateTabTyp, n INTEGER) IS

BEGIN

FOR i IN 1..n LOOP

tab(i) := SYSDATE;

END LOOP;

END initialize;

PROCEDURE initialize (tab OUT NumTabTyp, n INTEGER) IS

BEGIN

FOR i IN 1..n LOOP

tab(i) := 0.0;

END LOOP;

END initialize;

BEGIN

initialize(hiredate_tab, 50); -- calls first (DateTabTyp) version

initialize(sal_tab, 100); -- calls second (NumTabTyp) version

END;

Guidelines for Overloading with Numeric Types

You can overload two subprograms if their formal parameters differ only in numeric datatype. This technique might be useful in writing mathematical application programming interfaces (APIs), where several versions of a function could use the same name, each accepting a different numeric type. For example, a function accepting

BINARY_FLOAT

might be faster, while a function accepting

BINARY_DOUBLE

might provide more precision.

To avoid problems or unexpected results passing parameters to such overloaded subprograms:

■

Make sure to test that the expected version of a subprogram is called for each set of expected parameters. For example, if you have overloaded functions that accept

BINARY_FLOAT

and

BINARY_DOUBLE

, which is called if you pass a

VARCHAR2 literal such as '5.0'?

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Overloading Subprogram Names

■

Qualify numeric literals and use conversion functions to make clear what the intended parameter types are. For example, use literals such as

5.0f

(for

BINARY_FLOAT

5.0d

(for

BINARY_DOUBLE

), or conversion functions such as

TO_BINARY_FLOAT()

TO_BINARY_DOUBLE()

, and

TO_NUMBER()

PL/SQL looks for matching numeric parameters starting with

PLS_INTEGER

BINARY_INTEGER

, then

NUMBER

, then

BINARY_FLOAT

, then

BINARY_DOUBLE

. The first overloaded subprogram that matches the supplied parameters is used. A

VARCHAR2

value can match a

NUMBER

BINARY_FLOAT

, or

BINARY_DOUBLE parameter.

For example, consider the

SQRT

function, which takes a single parameter. There are overloaded versions that accept a

NUMBER

, a

BINARY_FLOAT

, or a

BINARY_DOUBLE parameter. If you pass a

PLS_INTEGER

parameter, the first matching overload (using the order given in the preceding paragraph) is the one with a

NUMBER

parameter, which is likely to be the slowest. To use one of the faster versions, use the

TO_BINARY_FLOAT

TO_BINARY_DOUBLE

functions to convert the parameter to the right datatype.

For another example, consider the

ATAN2

function, which takes two parameters of the same type. If you pass two parameters of the same type, you can predict which overloaded version is used through the same rules as before. If you pass parameters of different types, for example one

PLS_INTEGER

and one

BINARY_FLOAT

, PL/SQL tries to find a match where both parameters use the higher type. In this case, that is the version of

ATAN2

that takes two

BINARY_FLOAT

parameters; the

PLS_INTEGER parameter is converted upwards.

The preference for converting upwards holds in more complicated situations. For example, you might have a complex function that takes two parameters of different types. One overloaded version might take a

PLS_INTEGER

and a

BINARY_FLOAT parameter. Another overloaded version might take a

NUMBER

and a

BINARY_DOUBLE parameter. What happens if you call this procedure name and pass two

NUMBER parameters? PL/SQL looks upward first to find the overloaded version where the second parameter is

BINARY_FLOAT

. Because this parameter is a closer match than the

BINARY_DOUBLE

parameter in the other overload, PL/SQL then looks downward and converts the first

NUMBER

parameter to

PLS_INTEGER

Restrictions on Overloading

Only local or packaged subprograms, or type methods, can be overloaded. You cannot overload standalone subprograms.

You cannot overload two subprograms if their formal parameters differ only in name or parameter mode. For example, you cannot overload the following two procedures:

Example 8–9 Restrictions on Overloading PL/SQL Procedures

DECLARE

PROCEDURE balance (acct_no IN INTEGER) IS

BEGIN NULL; END;

PROCEDURE balance (acct_no OUT INTEGER) IS

BEGIN NULL; END;

BEGIN

DBMS_OUTPUT.PUT_LINE('The following procedure call raises an error.');

-- balance(100); raises an error because the procedure declaration is not unique

END;

Using PL/SQL Subprograms

8-11

How Subprogram Calls Are Resolved

You cannot overload subprograms whose parameters differ only in subtype. For example, you cannot overload procedures where one accepts an

INTEGER

parameter and the other accepts a

REAL

parameter, even though

INTEGER

and

REAL

are both subtypes of

NUMBER

and so are in the same family.

You cannot overload two functions that differ only in the datatype of the return value, even if the types are in different families. For example, you cannot overload two functions where one returns

BOOLEAN

and the other returns

INTEGER

How Subprogram Calls Are Resolved

Figure 8–1

shows how the PL/SQL compiler resolves subprogram calls. When the compiler encounters a procedure or function call, it tries to find a declaration that matches the call. The compiler searches first in the current scope and then, if necessary, in successive enclosing scopes. The compiler looks more closely when it finds one or more subprogram declarations in which the subprogram name matches the name of the called subprogram.

To resolve a call among possibly like-named subprograms at the same level of scope, the compiler must find an exact match between the actual and formal parameters.

They must match in number, order, and datatype (unless some formal parameters were assigned default values). If no match is found or if multiple matches are found, the compiler generates a semantic error.

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How Subprogram Calls Are Resolved

Figure 8–1 How the PL/SQL Compiler Resolves Calls

encounter subprogram call compare name of called subprogram with names of any subprograms declared in current scope go to enclosing scope match(es) found?

Yes compare actual parameter list in subprogram call with formal parameter list in subprogram declaration(s)

Yes enclosing scope?

No match(es) found?

Yes multiple matches?

Yes

No resolve call generate semantic error

Example 8–10 calls the enclosing procedure

swap

from the function balance

, generating an error because neither declaration of swap

within the current scope matches the procedure call.

Example 8–10 Resolving PL/SQL Procedure Names

DECLARE

PROCEDURE swap (n1 NUMBER, n2 NUMBER) IS

num1 NUMBER;

num2 NUMBER;

FUNCTION balance (bal NUMBER) RETURN NUMBER IS

x NUMBER := 10;

PROCEDURE swap (d1 DATE, d2 DATE) IS BEGIN NULL; END;

PROCEDURE swap (b1 BOOLEAN, b2 BOOLEAN) IS BEGIN NULL; END;

BEGIN

DBMS_OUTPUT.PUT_LINE('The following raises an error');

-- swap(num1, num2); wrong number or types of arguments in call to 'SWAP'

RETURN x;

END balance;

Using PL/SQL Subprograms

8-13

How Subprogram Calls Are Resolved

BEGIN NULL;END swap;

BEGIN

NULL;

END;

How Overloading Works with Inheritance

The overloading algorithm allows substituting a subtype value for a formal parameter that is a supertype. This capability is known as substitutability. If more than one instance of an overloaded procedure matches the procedure call, the following rules apply to determine which procedure is called:

If the only difference in the signatures of the overloaded procedures is that some parameters are object types from the same supertype-subtype hierarchy, the closest match is used. The closest match is one where all the parameters are at least as close as any other overloaded instance, as determined by the depth of inheritance between the subtype and supertype, and at least one parameter is closer.

A semantic error occurs when two overloaded instances match, and some argument types are closer in one overloaded procedure to the actual arguments than in any other instance.

A semantic error also occurs if some parameters are different in their position within the object type hierarchy, and other parameters are of different datatypes so that an implicit conversion would be necessary.

For example, create a type hierarchy with three levels and then declare two overloaded instances of a function, where the only difference in argument types is their position in this type hierarchy, as shown in

Example 8–11

. We declare a variable of type final_t

, then call the overloaded function. The instance of the function that is executed is the one that accepts a sub_t

parameter, because that type is closer to final_t

in the hierarchy than super_t

is.

Example 8–11 Resolving PL/SQL Functions With Inheritance

CREATE OR REPLACE TYPE super_t AS OBJECT

(n NUMBER) NOT final;

CREATE OR REPLACE TYPE sub_t UNDER super_t

(n2 NUMBER) NOT final;

CREATE OR REPLACE TYPE final_t UNDER sub_t

(n3 NUMBER);

CREATE OR REPLACE PACKAGE p IS

FUNCTION func (arg super_t) RETURN NUMBER;

FUNCTION func (arg sub_t) RETURN NUMBER;

END;

CREATE OR REPLACE PACKAGE BODY p IS

FUNCTION func (arg super_t) RETURN NUMBER IS BEGIN RETURN 1; END;

FUNCTION func (arg sub_t) RETURN NUMBER IS BEGIN RETURN 2; END;

END;

DECLARE

v final_t := final_t(1,2,3);

BEGIN

DBMS_OUTPUT.PUT_LINE(p.func(v)); -- prints 2

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Oracle Database PL/SQL User’s Guide and Reference

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

END;

Example 8–11

, the choice of which instance to call is made at compile time. In

Example 8–12 , this choice is made dynamically. We declare

as an instance of super_t

, but because we assign a value of sub_t

to it, the appropriate instance of the function is called. This feature is known as dynamic dispatch.

Example 8–12 Resolving PL/SQL Functions With Inheritance Dynamically

CREATE TYPE super_t AS OBJECT

(n NUMBER, MEMBER FUNCTION func RETURN NUMBER) NOT final;

CREATE TYPE BODY super_t AS

MEMBER FUNCTION func RETURN NUMBER IS BEGIN RETURN 1; END; END;

CREATE OR REPLACE TYPE sub_t UNDER super_t

(n2 NUMBER,

OVERRIDING MEMBER FUNCTION func RETURN NUMBER) NOT final;

CREATE TYPE BODY sub_t AS

OVERRIDING MEMBER FUNCTION func RETURN NUMBER IS BEGIN RETURN 2; END; END;

CREATE OR REPLACE TYPE final_t UNDER sub_t

(n3 NUMBER);

DECLARE

v super_t := final_t(1,2,3);

BEGIN

DBMS_OUTPUT.PUT_LINE(v.func); -- prints 2

END;

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

By default, stored procedures and SQL methods execute with the privileges of their owner, not their current user. Such definer's rights subprograms are bound to the schema in which they reside, allowing you to refer to objects in the same schema without qualifying their names. For example, if schemas

and

both have a table called departments

, a procedure owned by

can refer to departments

rather than

HR.departments

. If user

calls

's procedure, the procedure still accesses the departments

table owned by

If you compile the same procedure in both schemas, you can define the schema name as a variable in SQL*Plus and refer to the table like

&schema..departments

. The code is portable, but if you change it, you must recompile it in each schema.

A more maintainable way is to use the

AUTHID

clause, which makes stored procedures and SQL methods execute with the privileges and schema context of the calling user.

You can create one instance of the procedure, and many users can call it to access their own data.

Such invoker's rights subprograms are not bound to a particular schema. The following version of procedure create_dept

executes with the privileges of the calling user and inserts rows into that user's departments

table:

Using PL/SQL Subprograms

8-15

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

Example 8–13 Specifying Invoker's Rights With a Procedure

CREATE OR REPLACE PROCEDURE create_dept (

v_deptno NUMBER,

v_dname VARCHAR2,

v_mgr NUMBER,

v_loc NUMBER)

AUTHID CURRENT_USER AS

BEGIN

INSERT INTO departments VALUES (v_deptno, v_dname, v_mgr, v_loc);

END;

CALL create_dept(44, 'Information Technology', 200, 1700);

Advantages of Invoker's Rights

Invoker's rights subprograms let you reuse code and centralize application logic. They are especially useful in applications that store data using identical tables in different schemas. All the schemas in one instance can call procedures owned by a central schema. You can even have schemas in different instances call centralized procedures using a database link.

Consider a company that uses a stored procedure to analyze sales. If the company has several schemas, each with a similar

SALES

table, normally it would also need several copies of the stored procedure, one in each schema.

To solve the problem, the company installs an invoker's rights version of the stored procedure in a central schema. Now, all the other schemas can call the same procedure, which queries the appropriate to

SALES

table in each case.

You can restrict access to sensitive data by calling from an invoker's rights subprogram to a definer's rights subprogram that queries or updates the table containing the sensitive data. Although multiple users can call the invoker's rights subprogram, they do not have direct access to the sensitive data.

Specifying the Privileges for a Subprogram with the AUTHID Clause

To implement invoker's rights, use the

AUTHID

clause, which specifies whether a subprogram executes with the privileges of its owner or its current user. It also specifies whether external references (that is, references to objects outside the subprogram) are resolved in the schema of the owner or the current user.

The

AUTHID

clause is allowed only in the header of a standalone subprogram, a package spec, or an object type spec. In the

CREATE FUNCTION

CREATE

PROCEDURE

CREATE PACKAGE

, or

CREATE TYPE

statement, you can include either

AUTHID CURRENT_USER

AUTHID DEFINER

immediately before the

AS keyword that begins the declaration section.

DEFINER

is the default option. In a package or object type, the

AUTHID

clause applies to all subprograms.

Most supplied PL/SQL packages (such as

DBMS_LOB

DBMS_PIPE

DBMS_ROWID

DBMS_SQL

, and

UTL_REF

) are invoker's rights packages.

Who Is the Current User During Subprogram Execution?

In a sequence of calls, whenever control is inside an invoker's rights subprogram, the current user is the session user. When a definer's rights subprogram is called, the

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Oracle Database PL/SQL User’s Guide and Reference

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause) owner of that subprogram becomes the current user. The current user might change as new subprograms are called or as subprograms exit.

To verify who the current user is at any time, you can check the

USER_USERS

data dictionary view. Inside an invoker's rights subprogram, the value from this view might be different from the value of the

USER

built-in function, which always returns the name of the session user.

How External References Are Resolved in Invoker's Rights Subprograms

If you specify

AUTHID CURRENT_USER

, the privileges of the current user are checked at run time, and external references are resolved in the schema of the current user.

However, this applies only to external references in:

■

SELECT

INSERT

UPDATE

, and

DELETE

data manipulation statements

The

LOCK TABLE

transaction control statement

OPEN

and

OPEN-FOR

cursor control statements

EXECUTE IMMEDIATE

and

OPEN-FOR-USING

dynamic SQL statements

■

SQL statements parsed using

DBMS_SQL.PARSE()

For all other statements, the privileges of the owner are checked at compile time, and external references are resolved in the schema of the owner. For example, the assignment statement in

Example 8–14 refers to the packaged function

num_above_salary

in the emp_actions

package in

Example 1–13 on page 1-14.

This external reference is resolved in the schema of the owner of procedure above_salary

Example 8–14 Resolving External References in an Invoker's Rights Subprogram

CREATE PROCEDURE above_salary (emp_id IN NUMBER)

AUTHID CURRENT_USER AS

emps NUMBER;

BEGIN

emps := emp_actions.num_above_salary(emp_id);

DBMS_OUTPUT.PUT_LINE( 'Number of employees with higher salary: ' ||

TO_CHAR(emps));

END;

CALL above_salary(120);

The Need for Template Objects in Invoker's Rights Subprograms

The PL/SQL compiler must resolve all references to tables and other objects at compile time. The owner of an invoker's rights subprogram must have objects in the same schema with the right names and columns, even if they do not contain any data. At run time, the corresponding objects in the caller's schema must have matching definitions. Otherwise, you get an error or unexpected results, such as ignoring table columns that exist in the caller's schema but not in the schema that contains the subprogram.

Overriding Default Name Resolution in Invoker's Rights Subprograms

Occasionally, you might want an unqualified name to refer to some particular schema, not the schema of the caller. In the same schema as the invoker's rights subprogram, create a public synonym for the table, procedure, function, or other object using the

CREATE SYNONYM

statement:

Using PL/SQL Subprograms

8-17

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

CREATE PUBLIC SYNONYM emp FOR hr.employees;

When the invoker's rights subprogram refers to this name, it will match the synonym in its own schema, which resolves to the object in the specified schema. This technique does not work if the calling schema already has a schema object or private synonym with the same name. In that case, the invoker's rights subprogram must fully qualify the reference.

Granting Privileges on Invoker's Rights Subprograms

To call a subprogram directly, users must have the

EXECUTE

privilege on that subprogram. By granting the privilege, you allow a user to:

■

Call the subprogram directly

Compile functions and procedures that call the subprogram

For external references resolved in the current user's schema (such as those in DML statements), the current user must have the privileges needed to access schema objects referenced by the subprogram. For all other external references (such as function calls), the owner's privileges are checked at compile time, and no run-time check is done.

A definer's rights subprogram operates under the security domain of its owner, no matter who is executing it. The owner must have the privileges needed to access schema objects referenced by the subprogram.

You can write a program consisting of multiple subprograms, some with definer's rights and others with invoker's rights. Then, you can use the

EXECUTE

privilege to restrict program entry points. That way, users of an entry-point subprogram can execute the other subprograms indirectly but not directly.

Granting Privileges on an Invoker's Rights Subprogram: Example

Suppose user

UTIL

grants the

EXECUTE

privilege on subprogram

FFT

to user

APP

GRANT EXECUTE ON util.fft TO app;

Now, user

APP

can compile functions and procedures that call subprogram

FFT

. At

run time, no privilege checks on the calls are done. As Figure 8–2

shows, user

UTIL need not grant the

EXECUTE

privilege to every user who might call

FFT

indirectly.

Since subprogram util.fft

is called directly only from invoker's rights subprogram app.entry

, user util

must grant the

EXECUTE

privilege only to user

APP

. When

UTIL.FFT

is executed, its current user could be

APP

SCOTT

, or

BLAKE

even though

SCOTT

and

BLAKE

were not granted the

EXECUTE

privilege.

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Oracle Database PL/SQL User’s Guide and Reference

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

Figure 8–2 Indirect Calls to an Invoker's Rights Subprogram

Schema

SCOTT proc1

Schema

UTIL

Schema

APP entry

(IR)

Schema

BLAKE fft proc2

Using Roles with Invoker's Rights Subprograms

The use of roles in a subprogram depends on whether it executes with definer's rights or invoker's rights. Within a definer's rights subprogram, all roles are disabled. Roles are not used for privilege checking, and you cannot set roles.

Within an invoker's rights subprogram, roles are enabled (unless the subprogram was called directly or indirectly by a definer's rights subprogram). Roles are used for privilege checking, and you can use native dynamic SQL to set roles for the session.

However, you cannot use roles to grant privileges on template objects because roles apply at run time, not at compile time.

Using Views and Database Triggers with Invoker's Rights Subprograms

For invoker's rights subprograms executed within a view expression, the schema that created the view, not the schema that is querying the view, is considered to be the current user. This rule also applies to database triggers.

Using Database Links with Invoker's Rights Subprograms

You can create a database link to use invoker's rights:

CREATE DATABASE LINK link_name CONNECT TO CURRENT_USER

USING connect_string;

A current-user link lets you connect to a remote database as another user, with that user's privileges. To connect, Oracle uses the username of the current user (who must be a global user). Suppose an invoker's rights subprogram owned by user

OE references the following database link. If global user

calls the subprogram, it connects to the Dallas database as user

, who is the current user.

CREATE DATABASE LINK dallas CONNECT TO CURRENT_USER USING

...

If it were a definer's rights subprogram, the current user would be

, and the subprogram would connect to the Dallas database as global user

Using PL/SQL Subprograms

8-19

Using Invoker's Rights Versus Definer's Rights (AUTHID Clause)

Using Object Types with Invoker's Rights Subprograms

To define object types for use in any schema, specify the

AUTHID CURRENT_USER clause. For information on object types, see Oracle Database Application Developer's

Guide - Object-Relational Features.

Suppose user

creates the following object type:

Example 8–15 Creating an Object Type With AUTHID CURRENT USER

CREATE TYPE person_typ AUTHID CURRENT_USER AS OBJECT (

person_id NUMBER,

person_name VARCHAR2(30),

person_job VARCHAR2(10),

STATIC PROCEDURE new_person_typ (

person_id NUMBER, person_name VARCHAR2, person_job VARCHAR2,

schema_name VARCHAR2, table_name VARCHAR2),

MEMBER PROCEDURE change_job (SELF IN OUT NOCOPY person_typ, new_job VARCHAR2)

);

CREATE TYPE BODY person_typ AS

STATIC PROCEDURE new_person_typ (

person_id NUMBER, person_name VARCHAR2, person_job VARCHAR2,

schema_name VARCHAR2, table_name VARCHAR2) IS

sql_stmt VARCHAR2(200);

BEGIN

sql_stmt := 'INSERT INTO ' || schema_name || '.'

|| table_name || ' VALUES (HR.person_typ(:1, :2, :3))';

EXECUTE IMMEDIATE sql_stmt USING person_id, person_name, person_job;

END;

MEMBER PROCEDURE change_job (SELF IN OUT NOCOPY person_typ, new_job VARCHAR2) IS

BEGIN

person_job := new_job;

END;

Then, user

grants the

EXECUTE

privilege on object type person_typ

to user

GRANT EXECUTE ON person_typ TO OE;

Finally, user

creates an object table to store objects of type person_typ

, then calls procedure new_person_typ

to populate the table:

CONNECT oe/oe;

CREATE TABLE person_tab OF hr.person_typ;

BEGIN

hr.person_typ.new_person_typ(1001, 'Jane Smith', 'CLERK', 'oe', 'person_tab');

hr.person_typ.new_person_typ(1002, 'Joe Perkins', 'SALES','oe', 'person_tab');

hr.person_typ.new_person_typ(1003, 'Robert Lange', 'DEV','oe', 'person_tab');

END;

The calls succeed because the procedure executes with the privileges of its current user

(

), not its owner (

For subtypes in an object type hierarchy, the following rules apply:

■

If a subtype does not explicitly specify an

AUTHID

clause, it inherits the

AUTHID

of its supertype.

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Oracle Database PL/SQL User’s Guide and Reference

Using Recursion with PL/SQL

■

If a subtype does specify an

AUTHID

clause, its

AUTHID

must match the

AUTHID

of its supertype. Also, if the

AUTHID

DEFINER

, both the supertype and subtype must have been created in the same schema.

Calling Invoker's Rights Instance Methods

An invoker's rights instance method executes with the privileges of the invoker, not the creator of the instance. Suppose that person_typ

is an invoker's rights object type as created in

Example 8–15 , and that user

creates p1

, an object of type person_typ

. If user

calls instance method change_job

to operate on object p1

, the current user of the method is

, not

, as shown in

Example 8–16 .

Example 8–16 Calling an Invoker's Rights Instance Methods

-- oe creates a procedure that calls change_job

CREATE PROCEDURE reassign (p IN OUT NOCOPY hr.person_typ, new_job VARCHAR2) AS

BEGIN

p.change_job(new_job); -- executes with the privileges of oe

END;

-- OE grants EXECUTE to HR on procedure reassign

GRANT EXECUTE ON reassign to HR;

CONNECT hr/hr

-- user hr passes a person_typ object to the procedure reassign

DECLARE

p1 person_typ;

BEGIN

p1 := person_typ(1004, 'June Washburn', 'SALES');

oe.reassign(p1, 'CLERK'); -- current user is oe, not hr

END;

Using Recursion with PL/SQL

Recursion is a powerful technique for simplifying the design of algorithms. Basically, recursion means self-reference. In a recursive mathematical sequence, each term is derived by applying a formula to preceding terms. The Fibonacci sequence (0, 1, 1, 2, 3,

5, 8, 13, 21, ...), is an example. Each term in the sequence (after the second) is the sum of the two terms that immediately precede it.

In a recursive definition, something is defined as simpler versions of itself. Consider the definition of n factorial (n!), the product of all integers from 1 to n: n! = n * (n - 1)!

What Is a Recursive Subprogram?

A recursive subprogram is one that calls itself. Each recursive call creates a new instance of any items declared in the subprogram, including parameters, variables, cursors, and exceptions. Likewise, new instances of SQL statements are created at each level in the recursive descent.

Be careful where you place a recursive call. If you place it inside a cursor

FOR

loop or between

OPEN

and

statements, another cursor is opened at each call, which might exceed the limit set by the Oracle initialization parameter

OPEN_CURSORS

Using PL/SQL Subprograms

8-21

Calling External Subprograms

There must be at least two paths through a recursive subprogram: one that leads to the recursive call and one that does not. At least one path must lead to a terminating condition. Otherwise, the recursion would go on until PL/SQL runs out of memory and raises the predefined exception

STORAGE_ERROR

Calling External Subprograms

Although PL/SQL is a powerful, flexible language, some tasks are more easily done in another language. Low-level languages such as C are very fast. Widely used languages such as Java have reusable libraries for common design patterns.

You can use PL/SQL call specs to invoke external subprograms written in other languages, making their capabilities and libraries available from PL/SQL. For example, you can call Java stored procedures from any PL/SQL block, subprogram, or package. For more information about Java stored procedures, see Oracle Database Java

Developer's Guide.

If the following Java class is stored in the database, it can be called as shown in

Example 8–17 .

import java.sql.*; import oracle.jdbc.driver.*; public class Adjuster { public static void raiseSalary (int empNo, float percent) throws SQLException {

Connection conn = new OracleDriver().defaultConnection();

String sql = "UPDATE employees SET salary = salary * ?

WHERE employee_id = ?"; try {

PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setFloat(1, (1 + percent / 100)); pstmt.setInt(2, empNo); pstmt.executeUpdate(); pstmt.close();

} catch (SQLException e)

{System.err.println(e.getMessage());}

}

The class

Adjuster

has one method, which raises the salary of an employee by a given percentage. Because raiseSalary

is a void

method, you publish it as a procedure using the call specification shown in

Example 8–17 and then can call the

procedure raise_salary

from an anonymous PL/SQL block.

Example 8–17 Calling an External Procedure From PL/SQL

CREATE OR REPLACE PROCEDURE raise_salary (empid NUMBER, pct NUMBER)

AS LANGUAGE JAVA

NAME 'Adjuster.raiseSalary(int, float)';

DECLARE

emp_id NUMBER := 120;

percent NUMBER := 10;

BEGIN

-- get values for emp_id and percent

raise_salary(emp_id, percent); -- call external subprogram

END;

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Oracle Database PL/SQL User’s Guide and Reference

Controlling Side Effects of PL/SQL Subprograms

Java call specs cannot be declared as nested procedures, but can be specified in object type specifications, object type bodies, PL/SQL package specifications, PL/SQL package bodies, and as top level PL/SQL procedures and functions.

Example 8–18 shows a call to a Java function from a PL/SQL procedure.

Example 8–18 Calling a Java Function From PL/SQL

-- the following nested Java call spec is not valid, throws PLS-00999

-- CREATE PROCEDURE sleep (milli_seconds in number) IS

-- PROCEDURE java_sleep (milli_seconds IN NUMBER) AS ...

-- first, create the Java call spec, then call from a PL/SQL procedure

CREATE PROCEDURE java_sleep (milli_seconds IN NUMBER)

AS LANGUAGE JAVA NAME 'java.lang.Thread.sleep(long)';

CREATE PROCEDURE sleep (milli_seconds in number) IS

-- the following nested PROCEDURE spec is not legal

-- PROCEDURE java_sleep (milli_seconds IN NUMBER)

-- AS LANGUAGE JAVA NAME 'java.lang.Thread.sleep(long)';

BEGIN

DBMS_OUTPUT.PUT_LINE(DBMS_UTILITY.get_time());

java_sleep (milli_seconds);

DBMS_OUTPUT.PUT_LINE(DBMS_UTILITY.get_time());

END;

External C subprograms are used to interface with embedded systems, solve engineering problems, analyze data, or control real-time devices and processes.

External C subprograms extend the functionality of the database server, and move computation-bound programs from client to server, where they execute faster. For more information about external C subprograms, see Oracle Database Application

Developer's Guide - Fundamentals.

Controlling Side Effects of PL/SQL Subprograms

To be callable from SQL statements, a stored function (and any subprograms called by that function) must obey certain purity rules, which are meant to control side effects:

■

When called from a

SELECT

statement or a parallelized

INSERT

UPDATE

, or

DELETE

statement, the function cannot modify any database tables.

When called from an

INSERT

UPDATE

, or

DELETE

statement, the function cannot query or modify any database tables modified by that statement.

■

When called from a

SELECT

INSERT

UPDATE

, or

DELETE

statement, the function cannot execute SQL transaction control statements (such as

COMMIT

), session control statements (such as

SET ROLE

), or system control statements (such as

ALTER SYSTEM

). Also, it cannot execute DDL statements (such as

CREATE

) because they are followed by an automatic commit.

If any SQL statement inside the function body violates a rule, you get an error at run time (when the statement is parsed).

To check for violations of the rules, you can use the pragma (compiler directive)

RESTRICT_REFERENCES

. The pragma asserts that a function does not read or write database tables or package variables. For example, the following pragma asserts that

Using PL/SQL Subprograms

8-23

Understanding Subprogram Parameter Aliasing packaged function credit_ok

writes no database state (

WNDS

) and reads no package state (

RNPS

CREATE PACKAGE loans AS

FUNCTION credit_ok RETURN BOOLEAN;

PRAGMA RESTRICT_REFERENCES (credit_ok, WNDS, RNPS);

END loans;

A static

INSERT

UPDATE

, or

DELETE

statement always violates

WNDS

. It also violates

RNDS

(reads no database state) if it reads any columns. A dynamic

INSERT

UPDATE

, or

DELETE

statement always violates

WNDS

and

RNDS

For syntax details, see "RESTRICT_REFERENCES Pragma" on page 13-98. For more

information about the purity rules, see Oracle Database Application Developer's Guide -

Fundamentals.

Understanding Subprogram Parameter Aliasing

To optimize a subprogram call, the PL/SQL compiler can choose between two methods of parameter passing. With the by-value method, the value of an actual parameter is passed to the subprogram. With the by-reference method, only a pointer to the value is passed; the actual and formal parameters reference the same item.

The

NOCOPY

compiler hint increases the possibility of aliasing (that is, having two different names refer to the same memory location). This can occur when a global variable appears as an actual parameter in a subprogram call and then is referenced within the subprogram. The result is indeterminate because it depends on the method of parameter passing chosen by the compiler.

Example 8–19 , procedure

ADD_ENTRY

refers to varray

LEXICON

both as a parameter and as a global variable. When

ADD_ENTRY

is called, the identifiers

WORD_LIST

and

LEXICON

point to the same varray.

Example 8–19 Aliasing from Passing Global Variable with NOCOPY Hint

DECLARE

TYPE Definition IS RECORD (

word VARCHAR2(20),

meaning VARCHAR2(200));

TYPE Dictionary IS VARRAY(2000) OF Definition;

lexicon Dictionary := Dictionary();

PROCEDURE add_entry (word_list IN OUT NOCOPY Dictionary) IS

BEGIN

word_list(1).word := 'aardvark';

lexicon(1).word := 'aardwolf';

END;

BEGIN

lexicon.EXTEND;

add_entry(lexicon);

DBMS_OUTPUT.PUT_LINE(lexicon(1).word);

END;

The program prints aardwolf

if the compiler obeys the

NOCOPY

hint. The assignment to

WORD_LIST

is done immediately through a pointer, then is overwritten by the assignment to

LEXICON

The program prints aardvark

if the

NOCOPY

hint is omitted, or if the compiler does not obey the hint. The assignment to

WORD_LIST

uses an internal copy of the varray,

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Oracle Database PL/SQL User’s Guide and Reference

Understanding Subprogram Parameter Aliasing which is copied back to the actual parameter (overwriting the contents of

LEXICON

) when the procedure ends.

Aliasing can also occur when the same actual parameter appears more than once in a subprogram call. In

Example 8–20

, n2

is an

IN OUT

parameter, so the value of the actual parameter is not updated until the procedure exits. That is why the first

PUT_LINE

prints 10 (the initial value of n

) and the third

PUT_LINE

prints 20.

However, n3

is a

NOCOPY

parameter, so the value of the actual parameter is updated immediately. That is why the second

PUT_LINE

prints 30.

Example 8–20 Aliasing Passing Same Parameter Multiple Times

DECLARE

n NUMBER := 10;

PROCEDURE do_something (

n1 IN NUMBER,

n2 IN OUT NUMBER,

n3 IN OUT NOCOPY NUMBER) IS

BEGIN

n2 := 20;

DBMS_OUTPUT.put_line(n1); -- prints 10

n3 := 30;

DBMS_OUTPUT.put_line(n1); -- prints 30

END;

BEGIN

do_something(n, n, n);

DBMS_OUTPUT.put_line(n); -- prints 20

END;

Because they are pointers, cursor variables also increase the possibility of aliasing. In

Example 8–21 , after the assignment,

emp_cv2

is an alias of emp_cv1

; both point to the same query work area. The first fetch from emp_cv2

fetches the third row, not the first, because the first two rows were already fetched from emp_cv1

. The second fetch from emp_cv2

fails because emp_cv1

is closed.

Example 8–21 Aliasing from Assigning Cursor Variables to Same Work Area

DECLARE

TYPE EmpCurTyp IS REF CURSOR;

c1 EmpCurTyp;

c2 EmpCurTyp;

PROCEDURE get_emp_data (emp_cv1 IN OUT EmpCurTyp, emp_cv2 IN OUT EmpCurTyp) IS

emp_rec employees%ROWTYPE;

BEGIN

OPEN emp_cv1 FOR SELECT * FROM employees;

emp_cv2 := emp_cv1;

FETCH emp_cv1 INTO emp_rec; -- fetches first row

FETCH emp_cv1 INTO emp_rec; -- fetches second row

FETCH emp_cv2 INTO emp_rec; -- fetches third row

CLOSE emp_cv1;

DBMS_OUTPUT.put_line('The following raises an invalid cursor');

-- FETCH emp_cv2 INTO emp_rec; raises invalid cursor when get_emp_data is called

END;

BEGIN

get_emp_data(c1, c2);

END;

Using PL/SQL Subprograms

8-25

Understanding Subprogram Parameter Aliasing

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Oracle Database PL/SQL User’s Guide and Reference

Using PL/SQL Packages

This chapter shows how to bundle related PL/SQL code and data into a package. The package might include a set of procedures that forms an API, or a pool of type definitions and variable declarations. The package is compiled and stored in the database, where its contents can be shared by many applications.

This chapter contains these topics:

■

What Is a PL/SQL Package?

■

Advantages of PL/SQL Packages

Understanding The Package Specification

Understanding The Package Body

Some Examples of Package Features

■

How Package STANDARD Defines the PL/SQL Environment

Overview of Product-Specific Packages

Guidelines for Writing Packages

Separating Cursor Specs and Bodies with Packages

What Is a PL/SQL Package?

A package is a schema object that groups logically related PL/SQL types, variables, and subprograms. Packages usually have two parts, a specification (spec) and a body; sometimes the body is unnecessary. The specification is the interface to the package. It declares the types, variables, constants, exceptions, cursors, and subprograms that can be referenced from outside the package. The body defines the queries for the cursors and the code for the subprograms.

You can think of the spec as an interface and of the body as a black box. You can debug, enhance, or replace a package body without changing the package spec.

To create package specs, use the SQL statement

CREATE PACKAGE

. A

CREATE

PACKAGE BODY

statement defines the package body. For information on the

CREATE

PACKAGE

SQL statement, see Oracle Database SQL Reference. For information on the

CREATE PACKAGE BODY

SQL statement, see Oracle Database SQL Reference.

The spec holds public declarations, which are visible to stored procedures and other code outside the package. You must declare subprograms at the end of the spec after all other items (except pragmas that name a specific function; such pragmas must follow the function spec).

Using PL/SQL Packages

9-1

What Is a PL/SQL Package?

The body holds implementation details and private declarations, which are hidden from code outside the package. Following the declarative part of the package body is the optional initialization part, which holds statements that initialize package variables and do any other one-time setup steps.

The

AUTHID

clause determines whether all the packaged subprograms execute with the privileges of their definer (the default) or invoker, and whether their unqualified references to schema objects are resolved in the schema of the definer or invoker. For

more information, see "Using Invoker's Rights Versus Definer's Rights (AUTHID

Clause)" on page 8-15.

A call spec lets you map a package subprogram to a Java method or external C function. The call spec maps the Java or C name, parameter types, and return type to their SQL counterparts. To learn how to write Java call specs, see Oracle Database Java

Developer's Guide. To learn how to write C call specs, see Oracle Database Application

Developer's Guide - Fundamentals.

For information about PL/SQL packages provided with the Oracle database, see

Oracle Database PL/SQL Packages and Types Reference.

What Goes In a PL/SQL Package?

The following is contained in a PL/SQL package:

■

Get

and

Set

methods for the package variables, if you want to avoid letting other procedures read and write them directly.

Cursor declarations with the text of SQL queries. Reusing exactly the same query text in multiple locations is faster than retyping the same query each time with slight differences. It is also easier to maintain if you need to change a query that is used in many places.

Declarations for exceptions. Typically, you need to be able to reference these from different procedures, so that you can handle exceptions within called subprograms.

Declarations for procedures and functions that call each other. You do not need to worry about compilation order for packaged procedures and functions, making them more convenient than standalone stored procedures and functions when they call back and forth to each other.

■

Declarations for overloaded procedures and functions. You can create multiple variations of a procedure or function, using the same names but different sets of parameters.

Variables that you want to remain available between procedure calls in the same session. You can treat variables in a package like global variables.

■

Type declarations for PL/SQL collection types. To pass a collection as a parameter between stored procedures or functions, you must declare the type in a package so that both the calling and called subprogram can refer to it.

For additional information, see "Package Declaration" on page 13-85. For an examples

of a PL/SQL packages, see

Example 1–13, "Creating a Package and Package Body" on page 1-14 and

Example 9–3 on page 9-6. Only the declarations in the package spec are

visible and accessible to applications. Implementation details in the package body are hidden and inaccessible. You can change the body (implementation) without having to recompile calling programs.

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Oracle Database PL/SQL User’s Guide and Reference

Understanding The Package Specification

Advantages of PL/SQL Packages

Packages have a long history in software engineering, offering important features for reliable, maintainable, reusable code, often in team development efforts for large systems.

Modularity

Packages let you encapsulate logically related types, items, and subprograms in a named PL/SQL module. Each package is easy to understand, and the interfaces between packages are simple, clear, and well defined. This aids application development.

Easier Application Design

When designing an application, all you need initially is the interface information in the package specs. You can code and compile a spec without its body. Then, stored subprograms that reference the package can be compiled as well. You need not define the package bodies fully until you are ready to complete the application.

Information Hiding

With packages, you can specify which types, items, and subprograms are public

(visible and accessible) or private (hidden and inaccessible). For example, if a package contains four subprograms, three might be public and one private. The package hides the implementation of the private subprogram so that only the package (not your application) is affected if the implementation changes. This simplifies maintenance and enhancement. Also, by hiding implementation details from users, you protect the integrity of the package.

Added Functionality

Packaged public variables and cursors persist for the duration of a session. They can be shared by all subprograms that execute in the environment. They let you maintain data across transactions without storing it in the database.

Better Performance

When you call a packaged subprogram for the first time, the whole package is loaded into memory. Later calls to related subprograms in the package require no disk I/O.

Packages stop cascading dependencies and avoid unnecessary recompiling. For example, if you change the body of a packaged function, Oracle does not recompile other subprograms that call the function; these subprograms only depend on the parameters and return value that are declared in the spec, so they are only recompiled if the spec changes.

Understanding The Package Specification

The package specification contains public declarations. The declared items are accessible from anywhere in the package and to any other subprograms in the same

schema. Figure 9–1

illustrates the scoping.

Using PL/SQL Packages

9-3

Understanding The Package Specification

Figure 9–1 Package Scope

package spec package body procedure function procedure schema package spec package body function function procedure other objects

The spec lists the package resources available to applications. All the information your application needs to use the resources is in the spec. For example, the following declaration shows that the function named factorial

takes one argument of type

INTEGER

and returns a value of type

INTEGER

FUNCTION factorial (n INTEGER) RETURN INTEGER; -- returns n!

That is all the information you need to call the function. You need not consider its underlying implementation (whether it is iterative or recursive for example).

If a spec declares only types, constants, variables, exceptions, and call specs, the package body is unnecessary. Only subprograms and cursors have an underlying implementation. In

Example 9–1

, the package needs no body because it declares types, exceptions, and variables, but no subprograms or cursors. Such packages let you define global variables, usable by stored procedures and functions and triggers, that persist throughout a session.

Example 9–1 A Simple Package Specification Without a Body

CREATE PACKAGE trans_data AS -- bodiless package

TYPE TimeRec IS RECORD (

minutes SMALLINT,

hours SMALLINT);

TYPE TransRec IS RECORD (

category VARCHAR2(10),

account INT,

amount REAL,

time_of TimeRec);

minimum_balance CONSTANT REAL := 10.00;

number_processed INT;

insufficient_funds EXCEPTION;

END trans_data;

Referencing Package Contents

To reference the types, items, subprograms, and call specs declared within a package spec, use dot notation: package_name.type_name

package_name.item_name

package_name.subprogram_name

package_name.call_spec_name

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Oracle Database PL/SQL User’s Guide and Reference

Understanding The Package Body

You can reference package contents from database triggers, stored subprograms, 3GL application programs, and various Oracle tools. For example, you can call package procedures as shown in

Example 1–14, "Calling a Procedure in a Package" on page 1-15 or

Example 9–3 on page 9-6.

The following example calls the hire_employee

procedure from an anonymous block in a Pro*C program. The actual parameters emp_id

, emp_lname

, and emp_ fname

are host variables.

EXEC SQL EXECUTE

BEGIN emp_actions.hire_employee(:emp_id,:emp_lname,:emp_fname, ...);

Restrictions

You cannot reference remote packaged variables, either directly or indirectly. For example, you cannot call the a procedure through a database link if the procedure refers to a packaged variable.

Inside a package, you cannot reference host variables.

Understanding The Package Body

The package body contains the implementation of every cursor and subprogram declared in the package spec. Subprograms defined in a package body are accessible outside the package only if their specs also appear in the package spec. If a subprogram spec is not included in the package spec, that subprogram can only be called by other subprograms in the same package. A package body must be in the same schema as the package spec.

To match subprogram specs and bodies, PL/SQL does a token-by-token comparison of their headers. Except for white space, the headers must match word for word.

Otherwise, PL/SQL raises an exception, as

Example 9–2

shows.

Example 9–2 Matching Package Specifications and Bodies

CREATE PACKAGE emp_bonus AS

PROCEDURE calc_bonus (date_hired employees.hire_date%TYPE);

END emp_bonus;

CREATE PACKAGE BODY emp_bonus AS

-- the following parameter declaration raises an exception

-- because 'DATE' does not match employees.hire_date%TYPE

-- PROCEDURE calc_bonus (

date_hired DATE

) IS

-- the following is correct because there is an exact match

PROCEDURE calc_bonus (

date_hired employees.hire_date%TYPE

) IS

BEGIN

DBMS_OUTPUT.PUT_LINE('Employees hired on ' || date_hired || ' get bonus.');

END;

END emp_bonus;

The package body can also contain private declarations, which define types and items necessary for the internal workings of the package. The scope of these declarations is local to the package body. Therefore, the declared types and items are inaccessible except from within the package body. Unlike a package spec, the declarative part of a package body can contain subprogram bodies.

Using PL/SQL Packages

9-5

Some Examples of Package Features

Following the declarative part of a package body is the optional initialization part, which typically holds statements that initialize some of the variables previously declared in the package.

The initialization part of a package plays a minor role because, unlike subprograms, a package cannot be called or passed parameters. As a result, the initialization part of a package is run only once, the first time you reference the package.

Remember, if a package spec declares only types, constants, variables, exceptions, and call specs, the package body is unnecessary. However, the body can still be used to initialize items declared in the package spec.

Some Examples of Package Features

Consider the following package, named emp_admin

. The package specification declares the following types, items, and subprograms:

■

Type

EmpRecTyp

Cursor desc_salary

Exception invalid_salary

Functions hire_employee

and nth_highest_salary

■

Procedures fire_employee

and raise_salary

After writing the package, you can develop applications that reference its types, call its subprograms, use its cursor, and raise its exception. When you create the package, it is stored in an Oracle database for use by any application that has execute privilege on the package.

Example 9–3 Creating the emp_admin Package

-- create the audit table to track changes

CREATE TABLE emp_audit(date_of_action DATE, user_id VARCHAR2(20),

package_name VARCHAR2(30));

CREATE OR REPLACE PACKAGE emp_admin AS

-- Declare externally visible types, cursor, exception

TYPE EmpRecTyp IS RECORD (emp_id NUMBER, sal NUMBER);

CURSOR desc_salary RETURN EmpRecTyp;

invalid_salary EXCEPTION;

-- Declare externally callable subprograms

FUNCTION hire_employee (last_name VARCHAR2, first_name VARCHAR2,

email VARCHAR2, phone_number VARCHAR2, job_id VARCHAR2, salary NUMBER,

commission_pct NUMBER, manager_id NUMBER, department_id NUMBER)

RETURN NUMBER;

PROCEDURE fire_employee (emp_id NUMBER); -- overloaded subprogram

PROCEDURE fire_employee (emp_email VARCHAR2); -- overloaded subprogram

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER);

FUNCTION nth_highest_salary (n NUMBER) RETURN EmpRecTyp;

END emp_admin;

CREATE OR REPLACE PACKAGE BODY emp_admin AS

number_hired NUMBER; -- visible only in this package

-- Fully define cursor specified in package

CURSOR desc_salary RETURN EmpRecTyp IS

SELECT employee_id, salary FROM employees ORDER BY salary DESC;

-- Fully define subprograms specified in package

FUNCTION hire_employee (last_name VARCHAR2, first_name VARCHAR2,

email VARCHAR2, phone_number VARCHAR2, job_id VARCHAR2, salary NUMBER,

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Oracle Database PL/SQL User’s Guide and Reference

Some Examples of Package Features

commission_pct NUMBER, manager_id NUMBER, department_id NUMBER)

RETURN NUMBER IS

new_emp_id NUMBER;

BEGIN

SELECT employees_seq.NEXTVAL INTO new_emp_id FROM dual;

INSERT INTO employees VALUES (new_emp_id, last_name, first_name, email,

phone_number, SYSDATE, job_id, salary, commission_pct, manager_id,

department_id);

number_hired := number_hired + 1;

DBMS_OUTPUT.PUT_LINE('The number of employees hired is '

|| TO_CHAR(number_hired) );

RETURN new_emp_id;

END hire_employee;

PROCEDURE fire_employee (emp_id NUMBER) IS

BEGIN

DELETE FROM employees WHERE employee_id = emp_id;

END fire_employee;

PROCEDURE fire_employee (emp_email VARCHAR2) IS

BEGIN

DELETE FROM employees WHERE email = emp_email;

END fire_employee;

-- Define local function, available only inside package

FUNCTION sal_ok (jobid VARCHAR2, sal NUMBER) RETURN BOOLEAN IS

min_sal NUMBER;

max_sal NUMBER;

BEGIN

SELECT MIN(salary), MAX(salary) INTO min_sal, max_sal FROM employees

WHERE job_id = jobid;

RETURN (sal >= min_sal) AND (sal <= max_sal);

END sal_ok;

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER) IS

sal NUMBER(8,2);

jobid VARCHAR2(10);

BEGIN

SELECT job_id, salary INTO jobid, sal FROM employees

WHERE employee_id = emp_id;

IF sal_ok(jobid, sal + amount) THEN

UPDATE employees SET salary = salary + amount WHERE employee_id = emp_id;

ELSE

RAISE invalid_salary;

END IF;

EXCEPTION -- exception-handling part starts here

WHEN invalid_salary THEN

DBMS_OUTPUT.PUT_LINE('The salary is out of the specified range.');

END raise_salary;

FUNCTION nth_highest_salary (n NUMBER) RETURN EmpRecTyp IS

emp_rec EmpRecTyp;

BEGIN

OPEN desc_salary;

FOR i IN 1..n LOOP

FETCH desc_salary INTO emp_rec;

END LOOP;

CLOSE desc_salary;

RETURN emp_rec;

END nth_highest_salary;

BEGIN -- initialization part starts here

INSERT INTO emp_audit VALUES (SYSDATE, USER, 'EMP_ADMIN');

number_hired := 0;

END emp_admin;

Using PL/SQL Packages

9-7

How Package STANDARD Defines the PL/SQL Environment

-- calling the package procedures

DECLARE

new_emp_id NUMBER(6);

BEGIN

new_emp_id := emp_admin.hire_employee('Belden', 'Enrique', 'EBELDEN',

'555.111.2222', 'ST_CLERK', 2500, .1, 101, 110);

DBMS_OUTPUT.PUT_LINE('The new employee id is ' || TO_CHAR(new_emp_id) );

EMP_ADMIN.raise_salary(new_emp_id, 100);

DBMS_OUTPUT.PUT_LINE('The 10th highest salary is '||

TO_CHAR(emp_admin.nth_highest_salary(10).sal) || ', belonging to employee: '

|| TO_CHAR(emp_admin.nth_highest_salary(10).emp_id) );

emp_admin.fire_employee(new_emp_id);

-- you could also delete the newly added employee as follows:

-- emp_admin.fire_employee('EBELDEN');

END;

Remember, the initialization part of a package is run just once, the first time you reference the package. In the last example, only one row is inserted into the database table emp_audit

, and the variable number_hired

is initialized only once.

Every time the procedure hire_employee

is called, the variable number_hired

is updated. However, the count kept by number_hired

is session specific. That is, the count reflects the number of new employees processed by one user, not the number processed by all users.

PL/SQL allows two or more packaged subprograms to have the same name. This option is useful when you want a subprogram to accept similar sets of parameters that have different datatypes. For example, the emp_admin

package in

Example 9–3

defines two procedures named fire_employee

. The first procedure accepts a number, while the second procedure accepts string. Each procedure handles the data

appropriately. For the rules that apply to overloaded subprograms, see "Overloading

Subprogram Names" on page 8-10.

Private Versus Public Items in Packages

In the package emp_admin

, the package body declares a variable named number_ hired

, which is initialized to zero. Items declared in the body are restricted to use within the package. PL/SQL code outside the package cannot reference the variable number_hired

. Such items are called private.

Items declared in the spec of emp_admin

, such as the exception invalid_salary

, are visible outside the package. Any PL/SQL code can reference the exception invalid_salary

. Such items are called public.

To maintain items throughout a session or across transactions, place them in the declarative part of the package body. For example, the value of number_hired

is kept between calls to hire_employee

within the same session. The value is lost when the session ends.

To make the items public, place them in the package specification. For example, emp_ rec

declared in the spec of the package is available for general use.

How Package STANDARD Defines the PL/SQL Environment

A package named

STANDARD

defines the PL/SQL environment. The package spec globally declares types, exceptions, and subprograms, which are available automatically to PL/SQL programs. For example, package

STANDARD

declares function

ABS

, which returns the absolute value of its argument, as follows:

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Oracle Database PL/SQL User’s Guide and Reference

Overview of Product-Specific Packages

FUNCTION ABS (n NUMBER) RETURN NUMBER;

The contents of package

STANDARD

are directly visible to applications. You do not need to qualify references to its contents by prefixing the package name. For example, you might call

ABS

from a database trigger, stored subprogram, Oracle tool, or 3GL application, as follows: abs_diff := ABS(x - y);

If you declare your own version of

ABS

, your local declaration overrides the global declaration. You can still call the built-in function by specifying its full name: abs_diff := STANDARD.ABS(x - y);

Most built-in functions are overloaded. For example, package

STANDARD

contains the following declarations:

FUNCTION TO_CHAR (right DATE) RETURN VARCHAR2;

FUNCTION TO_CHAR (left NUMBER) RETURN VARCHAR2;

FUNCTION TO_CHAR (left DATE, right VARCHAR2) RETURN VARCHAR2;

FUNCTION TO_CHAR (left NUMBER, right VARCHAR2) RETURN VARCHAR2;

PL/SQL resolves a call to

TO_CHAR

by matching the number and datatypes of the formal and actual parameters.

Overview of Product-Specific Packages

Oracle and various Oracle tools are supplied with product-specific packages that define application programming interfaces (APIs) you can call from PL/SQL, SQL,

Java, or other programming environments. Here we mention a few of the more widely used ones. For more information, see Oracle Database PL/SQL Packages and Types

Reference.

About the DBMS_ALERT Package

Package

DBMS_ALERT

lets you use database triggers to alert an application when specific database values change. The alerts are transaction based and asynchronous

(that is, they operate independently of any timing mechanism). For example, a company might use this package to update the value of its investment portfolio as new stock and bond quotes arrive.

About the DBMS_OUTPUT Package

Package

DBMS_OUTPUT

enables you to display output from PL/SQL blocks, subprograms, packages, and triggers. The package is especially useful for displaying

PL/SQL debugging information. The procedure

PUT_LINE

outputs information to a buffer that can be read by another trigger, procedure, or package. You display the information by calling the procedure

GET_LINE

or by setting

SERVEROUTPUT ON

SQL*Plus.

Example 9–4 shows how to display output from a PL/SQL block.

Example 9–4 Using PUT_LINE in the DBMS_OUTPUT Package

REM set server output to ON to display output from DBMS_OUTPUT

SET SERVEROUTPUT ON

BEGIN

DBMS_OUTPUT.PUT_LINE('These are the tables that ' || USER || ' owns:');

FOR item IN (SELECT table_name FROM user_tables)

LOOP

DBMS_OUTPUT.PUT_LINE(item.table_name);

Using PL/SQL Packages

9-9

Guidelines for Writing Packages

END LOOP;

END;

About the DBMS_PIPE Package

Package

DBMS_PIPE

allows different sessions to communicate over named pipes. (A

pipe is an area of memory used by one process to pass information to another.) You can use the procedures

PACK_MESSAGE

and

SEND_MESSAGE

to pack a message into a pipe, then send it to another session in the same instance or to a waiting application such as a UNIX program.

At the other end of the pipe, you can use the procedures

RECEIVE_MESSAGE

and

UNPACK_MESSAGE

to receive and unpack (read) the message. Named pipes are useful in many ways. For example, you can write a C program to collect data, then send it through pipes to stored procedures in an Oracle database.

About the HTF and HTP Packages

Packages

HTF

and

HTP

allow your PL/SQL programs to generate HTML tags.

About the UTL_FILE Package

Package

UTL_FILE

lets PL/SQL programs read and write operating system (OS) text files. It provides a restricted version of standard OS stream file I/O, including open, put, get, and close operations.

When you want to read or write a text file, you call the function

FOPEN

, which returns a file handle for use in subsequent procedure calls. For example, the procedure

PUT_

LINE

writes a text string and line terminator to an open file, and the procedure

GET_

LINE

reads a line of text from an open file into an output buffer.

About the UTL_HTTP Package

Package

UTL_HTTP

allows your PL/SQL programs to make hypertext transfer protocol (HTTP) callouts. It can retrieve data from the Internet or call Oracle Web

Server cartridges. The package has two entry points, each of which accepts a URL

(uniform resource locator) string, contacts the specified site, and returns the requested data, which is usually in hypertext markup language (HTML) format.

About the UTL_SMTP Package

Package

UTL_SMTP

allows your PL/SQL programs to send electronic mails (emails) over Simple Mail Transfer Protocol (SMTP). The package provides interfaces to the

SMTP commands for an email client to dispatch emails to a SMTP server.

Guidelines for Writing Packages

When writing packages, keep them general so they can be reused in future applications. Become familiar with the Oracle-supplied packages, and avoid writing packages that duplicate features already provided by Oracle.

Design and define package specs before the package bodies. Place in a spec only those things that must be visible to calling programs. That way, other developers cannot build unsafe dependencies on your implementation details.

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Separating Cursor Specs and Bodies with Packages

To reduce the need for recompiling when code is changed, place as few items as possible in a package spec. Changes to a package body do not require recompiling calling procedures. Changes to a package spec require Oracle to recompile every stored subprogram that references the package.

Separating Cursor Specs and Bodies with Packages

You can separate a cursor specification (spec for short) from its body for placement in a package. That way, you can change the cursor body without having to change the cursor spec. For information on the cursor syntax, see

"Cursor Declaration" on page 13-33.

Example 9–5 , you use the

%ROWTYPE

attribute to provide a record type that represents a row in the database table employees

Example 9–5 Separating Cursor Specifications With Packages

CREATE PACKAGE emp_stuff AS

CURSOR c1 RETURN employees%ROWTYPE; -- declare cursor spec

END emp_stuff;

CREATE PACKAGE BODY emp_stuff AS

CURSOR c1 RETURN employees%ROWTYPE IS

SELECT * FROM employees WHERE salary > 2500; -- define cursor body

END emp_stuff;

The cursor spec has no

SELECT

statement because the

RETURN

clause specifies the datatype of the return value. However, the cursor body must have a

SELECT

statement and the same

RETURN

clause as the cursor spec. Also, the number and datatypes of items in the

SELECT

list and the

RETURN

clause must match.

Packaged cursors increase flexibility. For example, you can change the cursor body in the last example, without having to change the cursor spec.

From a PL/SQL block or subprogram, you use dot notation to reference a packaged cursor, as the following example shows:

DECLARE

emp_rec employees%ROWTYPE;

BEGIN

OPEN emp_stuff.c1;

LOOP

FETCH emp_stuff.c1 INTO emp_rec;

-- do processing here ...

EXIT WHEN emp_stuff.c1%NOTFOUND;

END LOOP;

CLOSE emp_stuff.c1;

END;

The scope of a packaged cursor is not limited to a PL/SQL block. When you open a packaged cursor, it remains open until you close it or you disconnect from the session.

Using PL/SQL Packages

9-11

Separating Cursor Specs and Bodies with Packages

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Oracle Database PL/SQL User’s Guide and Reference

Handling PL/SQL Errors

Run-time errors arise from design faults, coding mistakes, hardware failures, and many other sources. Although you cannot anticipate all possible errors, you can plan to handle certain kinds of errors meaningful to your PL/SQL program.

With many programming languages, unless you disable error checking, a run-time error such as stack overflow or division by zero stops normal processing and returns control to the operating system. With PL/SQL, a mechanism called exception handling lets you bulletproof your program so that it can continue operating in the presence of errors.

This chapter contains these topics:

■

Overview of PL/SQL Runtime Error Handling

■

Advantages of PL/SQL Exceptions

Summary of Predefined PL/SQL Exceptions

■

Defining Your Own PL/SQL Exceptions

How PL/SQL Exceptions Are Raised

How PL/SQL Exceptions Propagate

Reraising a PL/SQL Exception

Handling Raised PL/SQL Exceptions

Overview of PL/SQL Compile-Time Warnings

Overview of PL/SQL Runtime Error Handling

In PL/SQL, an error condition is called an exception. Exceptions can be internally defined (by the runtime system) or user defined. Examples of internally defined exceptions include division by zero

and out of memory

. Some common internal exceptions have predefined names, such as

ZERO_DIVIDE

and

STORAGE_ERROR

. The other internal exceptions can be given names.

You can define exceptions of your own in the declarative part of any PL/SQL block, subprogram, or package. For example, you might define an exception named insufficient_funds

to flag overdrawn bank accounts. Unlike internal exceptions, user-defined exceptions must be given names.

When an error occurs, an exception is raised. That is, normal execution stops and control transfers to the exception-handling part of your PL/SQL block or subprogram.

Internal exceptions are raised implicitly (automatically) by the run-time system.

User-defined exceptions must be raised explicitly by

RAISE

statements, which can also raise predefined exceptions.

Handling PL/SQL Errors

10-1

Overview of PL/SQL Runtime Error Handling

To handle raised exceptions, you write separate routines called exception handlers.

After an exception handler runs, the current block stops executing and the enclosing block resumes with the next statement. If there is no enclosing block, control returns to the host environment. For information on managing errors when using

BULK

COLLECT

, see

"Handling FORALL Exceptions with the %BULK_EXCEPTIONS

Attribute" on page 11-14.

Example 10–1 calculates a price-to-earnings ratio for a company. If the company has

zero earnings, the division operation raises the predefined exception

ZERO_DIVIDE

, the execution of the block is interrupted, and control is transferred to the exception handlers. The optional

OTHERS

handler catches all exceptions that the block does not name specifically.

Example 10–1 Runtime Error Handling

DECLARE

stock_price NUMBER := 9.73;

net_earnings NUMBER := 0;

pe_ratio NUMBER;

BEGIN

-- Calculation might cause division-by-zero error.

pe_ratio := stock_price / net_earnings;

DBMS_OUTPUT.PUT_LINE('Price/earnings ratio = ' || pe_ratio);

EXCEPTION -- exception handlers begin

-- Only one of the WHEN blocks is executed.

WHEN ZERO_DIVIDE THEN -- handles 'division by zero' error

DBMS_OUTPUT.PUT_LINE('Company must have had zero earnings.');

pe_ratio := NULL;

WHEN OTHERS THEN -- handles all other errors

DBMS_OUTPUT.PUT_LINE('Some other kind of error occurred.');

pe_ratio := NULL;

END; -- exception handlers and block end here

The last example illustrates exception handling. With some better error checking, we could have avoided the exception entirely, by substituting a null for the answer if the denominator was zero, as shown in the following example.

DECLARE

stock_price NUMBER := 9.73;

net_earnings NUMBER := 0;

pe_ratio NUMBER;

BEGIN

pe_ratio :=

CASE net_earnings

WHEN 0 THEN NULL

ELSE stock_price / net_earnings

end;

END;

Guidelines for Avoiding and Handling PL/SQL Errors and Exceptions

Because reliability is crucial for database programs, use both error checking and exception handling to ensure your program can handle all possibilities:

■

Add exception handlers whenever there is any possibility of an error occurring.

Errors are especially likely during arithmetic calculations, string manipulation, and database operations. Errors could also occur at other times, for example if a

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Oracle Database PL/SQL User’s Guide and Reference

Advantages of PL/SQL Exceptions

■

■ hardware failure with disk storage or memory causes a problem that has nothing to do with your code; but your code still needs to take corrective action.

Add error-checking code whenever you can predict that an error might occur if your code gets bad input data. Expect that at some time, your code will be passed incorrect or null parameters, that your queries will return no rows or more rows than you expect.

Make your programs robust enough to work even if the database is not in the state you expect. For example, perhaps a table you query will have columns added or deleted, or their types changed. You can avoid such problems by declaring individual variables with

%TYPE

qualifiers, and declaring records to hold query results with

%ROWTYPE

qualifiers.

Handle named exceptions whenever possible, instead of using WHEN OTHERS in exception handlers. Learn the names and causes of the predefined exceptions. If your database operations might cause particular ORA- errors, associate names with these errors so you can write handlers for them. (You will learn how to do that later in this chapter.)

Test your code with different combinations of bad data to see what potential errors arise.

Write out debugging information in your exception handlers. You might store such information in a separate table. If so, do it by making a call to a procedure declared with the

PRAGMA AUTONOMOUS_TRANSACTION

, so that you can commit your debugging information, even if you roll back the work that the main procedure was doing.

Carefully consider whether each exception handler should commit the transaction, roll it back, or let it continue. Remember, no matter how severe the error is, you want to leave the database in a consistent state and avoid storing any bad data.

Advantages of PL/SQL Exceptions

Using exceptions for error handling has several advantages. With exceptions, you can reliably handle potential errors from many statements with a single exception handler:

Example 10–2 Managing Multiple Errors With a Single Exception Handler

DECLARE

emp_column VARCHAR2(30) := 'last_name';

table_name VARCHAR2(30) := 'emp';

temp_var VARCHAR2(30);

BEGIN

temp_var := emp_column;

SELECT COLUMN_NAME INTO temp_var FROM USER_TAB_COLS

WHERE TABLE_NAME = 'EMPLOYEES' AND COLUMN_NAME = UPPER(emp_column);

-- processing here

temp_var := table_name;

SELECT OBJECT_NAME INTO temp_var FROM USER_OBJECTS

WHERE OBJECT_NAME = UPPER(table_name) AND OBJECT_TYPE = 'TABLE';

-- processing here

EXCEPTION

WHEN NO_DATA_FOUND THEN -- catches all 'no data found' errors

DBMS_OUTPUT.PUT_LINE ('No Data found for SELECT on ' || temp_var);

END;

Handling PL/SQL Errors

10-3

Summary of Predefined PL/SQL Exceptions

Instead of checking for an error at every point it might occur, just add an exception handler to your PL/SQL block. If the exception is ever raised in that block (or any sub-block), you can be sure it will be handled.

Sometimes the error is not immediately obvious, and could not be detected until later when you perform calculations using bad data. Again, a single exception handler can trap all division-by-zero errors, bad array subscripts, and so on.

If you need to check for errors at a specific spot, you can enclose a single statement or a group of statements inside its own

BEGIN-END

block with its own exception handler. You can make the checking as general or as precise as you like.

Isolating error-handling routines makes the rest of the program easier to read and understand.

Summary of Predefined PL/SQL Exceptions

An internal exception is raised automatically if your PL/SQL program violates an

Oracle rule or exceeds a system-dependent limit. PL/SQL predefines some common

Oracle errors as exceptions. For example, PL/SQL raises the predefined exception

NO_DATA_FOUND

if a

SELECT INTO

statement returns no rows.

You can use the pragma

EXCEPTION_INIT

to associate exception names with other

Oracle error codes that you can anticipate. To handle unexpected Oracle errors, you can use the

OTHERS

handler. Within this handler, you can call the functions

SQLCODE and

SQLERRM

to return the Oracle error code and message text. Once you know the error code, you can use it with pragma

EXCEPTION_INIT

and write a handler specifically for that error.

PL/SQL declares predefined exceptions globally in package

STANDARD

. You need not declare them yourself. You can write handlers for predefined exceptions using the names in the following table:

Exception

ACCESS_INTO_NULL

CASE_NOT_FOUND

COLLECTION_IS_NULL

CURSOR_ALREADY_OPEN

DUP_VAL_ON_INDEX

INVALID_CURSOR

INVALID_NUMBER

ORA Error SQLCODE Raise When ...

06530

06592

06531

06511

00001

01001

01722

-6530

-6592

-6531

-6511

-1

-1001

-1722

A program attempts to assign values to the attributes of an uninitialized object

None of the choices in the

WHEN

clauses of a

CASE statement is selected, and there is no

ELSE

clause.

A program attempts to apply collection methods other than

EXISTS

to an uninitialized nested table or varray, or the program attempts to assign values to the elements of an uninitialized nested table or varray.

A program attempts to open an already open cursor. A cursor must be closed before it can be reopened. A cursor

FOR

loop automatically opens the cursor to which it refers, so your program cannot open that cursor inside the loop.

A program attempts to store duplicate values in a column that is constrained by a unique index.

A program attempts a cursor operation that is not allowed, such as closing an unopened cursor. n a SQL statement, the conversion of a character string into a number fails because the string does not represent a valid number. (In procedural statements,

VALUE_ERROR

is raised.) This exception is also raised when the

LIMIT

-clause expression in a bulk

FETCH statement does not evaluate to a positive number.

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Defining Your Own PL/SQL Exceptions

Exception

LOGIN_DENIED

NO_DATA_FOUND

NOT_LOGGED_ON

PROGRAM_ERROR

ROWTYPE_MISMATCH

SELF_IS_NULL

STORAGE_ERROR

SUBSCRIPT_BEYOND_COUNT

SUBSCRIPT_OUTSIDE_LIMIT

SYS_INVALID_ROWID

TIMEOUT_ON_RESOURCE

TOO_MANY_ROWS

VALUE_ERROR

ZERO_DIVIDE

ORA Error SQLCODE Raise When ...

01017

01403

01012

06501

06504

30625

06500

06533

06532

01410

00051

01422

06502

01476

-1017

+100

-1012

-6501

-6504

-30625

-6500

-6533

-6532

-1410

-51

-1422

-6502

-1476

A program attempts to log on to Oracle with an invalid username or password.

SELECT INTO

statement returns no rows, or your program references a deleted element in a nested table or an uninitialized element in an index-by table.

Because this exception is used internally by some SQL functions to signal completion, you should not rely on this exception being propagated if you raise it within a function that is called as part of a query.

A program issues a database call without being connected to Oracle.

PL/SQL has an internal problem.

The host cursor variable and PL/SQL cursor variable involved in an assignment have incompatible return types. When an open host cursor variable is passed to a stored subprogram, the return types of the actual and formal parameters must be compatible.

A program attempts to call a

MEMBER

method, but the instance of the object type has not been initialized. The built-in parameter

SELF

points to the object, and is always the first parameter passed to a

MEMBER

method.

PL/SQL runs out of memory or memory has been corrupted.

A program references a nested table or varray element using an index number larger than the number of elements in the collection.

A program references a nested table or varray element using an index number (-1 for example) that is outside the legal range.

The conversion of a character string into a universal rowid fails because the character string does not represent a valid rowid.

A time out occurs while Oracle is waiting for a resource.

SELECT INTO

statement returns more than one row.

An arithmetic, conversion, truncation, or size-constraint error occurs. For example, when your program selects a column value into a character variable, if the value is longer than the declared length of the variable, PL/SQL aborts the assignment and raises

VALUE_ERROR

. In procedural statements,

VALUE_ERROR

is raised if the conversion of a character string into a number fails. (In SQL statements,

INVALID_NUMBER

is raised.)

A program attempts to divide a number by zero.

Defining Your Own PL/SQL Exceptions

PL/SQL lets you define exceptions of your own. Unlike predefined exceptions, user-defined exceptions must be declared and must be raised explicitly by

RAISE statements.

Handling PL/SQL Errors

10-5

Defining Your Own PL/SQL Exceptions

Declaring PL/SQL Exceptions

Exceptions can be declared only in the declarative part of a PL/SQL block, subprogram, or package. You declare an exception by introducing its name, followed by the keyword

EXCEPTION

. In the following example, you declare an exception named past_due

DECLARE

past_due EXCEPTION;

Exception and variable declarations are similar. But remember, an exception is an error condition, not a data item. Unlike variables, exceptions cannot appear in assignment statements or SQL statements. However, the same scope rules apply to variables and exceptions.

Scope Rules for PL/SQL Exceptions

You cannot declare an exception twice in the same block. You can, however, declare the same exception in two different blocks.

Exceptions declared in a block are considered local to that block and global to all its sub-blocks. Because a block can reference only local or global exceptions, enclosing blocks cannot reference exceptions declared in a sub-block.

If you redeclare a global exception in a sub-block, the local declaration prevails. The sub-block cannot reference the global exception, unless the exception is declared in a labeled block and you qualify its name with the block label: block_label.exception_name

Example 10–3 illustrates the scope rules:

Example 10–3 Scope of PL/SQL Exceptions

DECLARE

past_due EXCEPTION;

acct_num NUMBER;

BEGIN

DECLARE ---------- sub-block begins

past_due EXCEPTION; -- this declaration prevails

acct_num NUMBER;

due_date DATE := SYSDATE - 1;

todays_date DATE := SYSDATE;

BEGIN

IF due_date < todays_date THEN

RAISE past_due; -- this is not handled

END IF;

END; ------------- sub-block ends

EXCEPTION

WHEN past_due THEN -- does not handle raised exception

DBMS_OUTPUT.PUT_LINE('Handling PAST_DUE exception.');

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('Could not recognize PAST_DUE_EXCEPTION in this scope.');

END;

The enclosing block does not handle the raised exception because the declaration of past_due

in the sub-block prevails. Though they share the same name, the two past_due

exceptions are different, just as the two acct_num

variables share the same name but are different variables. Thus, the

RAISE

statement and the

WHEN

clause refer

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Defining Your Own PL/SQL Exceptions to different exceptions. To have the enclosing block handle the raised exception, you must remove its declaration from the sub-block or define an

OTHERS

handler.

Associating a PL/SQL Exception with a Number: Pragma EXCEPTION_INIT

To handle error conditions (typically

ORA-

messages) that have no predefined name, you must use the

OTHERS

handler or the pragma

EXCEPTION_INIT

. A pragma is a compiler directive that is processed at compile time, not at run time.

In PL/SQL, the pragma

EXCEPTION_INIT

tells the compiler to associate an exception name with an Oracle error number. That lets you refer to any internal exception by name and to write a specific handler for it. When you see an error stack, or sequence of error messages, the one on top is the one that you can trap and handle.

You code the pragma

EXCEPTION_INIT

in the declarative part of a PL/SQL block, subprogram, or package using the syntax

PRAGMA EXCEPTION_INIT(exception_name, -Oracle_error_number); where exception_name

is the name of a previously declared exception and the number is a negative value corresponding to an

ORA-

error number. The pragma must appear somewhere after the exception declaration in the same declarative section, as

shown in Example 10–4 .

Example 10–4 Using PRAGMA EXCEPTION_INIT

DECLARE

deadlock_detected EXCEPTION;

PRAGMA EXCEPTION_INIT(deadlock_detected, -60);

BEGIN

NULL; -- Some operation that causes an ORA-00060 error

EXCEPTION

WHEN deadlock_detected THEN

NULL; -- handle the error

END;

Defining Your Own Error Messages: Procedure RAISE_APPLICATION_ERROR

The procedure

RAISE_APPLICATION_ERROR

lets you issue user-defined

ORA-

error messages from stored subprograms. That way, you can report errors to your application and avoid returning unhandled exceptions.

To call

RAISE_APPLICATION_ERROR

, use the syntax raise_application_error( error_number, message[, {TRUE | FALSE}]); where error_number

is a negative integer in the range -20000 .. -20999 and message is a character string up to 2048 bytes long. If the optional third parameter is

TRUE

, the error is placed on the stack of previous errors. If the parameter is

FALSE

(the default), the error replaces all previous errors.

RAISE_APPLICATION_ERROR

is part of package

DBMS_STANDARD

, and as with package

STANDARD

, you do not need to qualify references to it.

An application can call raise_application_error

only from an executing stored subprogram (or method). When called, raise_application_error

ends the subprogram and returns a user-defined error number and message to the application.

The error number and message can be trapped like any Oracle error.

Handling PL/SQL Errors

10-7

Defining Your Own PL/SQL Exceptions

Example 10–5 , you call

raise_application_error

if an error condition of your choosing happens (in this case, if the current schema owns less than 1000 tables):

Example 10–5 Raising an Application Error With raise_application_error

DECLARE

num_tables NUMBER;

BEGIN

SELECT COUNT(*) INTO num_tables FROM USER_TABLES;

IF num_tables < 1000 THEN

/* Issue your own error code (ORA-20101) with your own error message.

Note that you do not need to qualify raise_application_error with

DBMS_STANDARD */

raise_application_error(-20101, 'Expecting at least 1000 tables');

ELSE

NULL; -- Do the rest of the processing (for the non-error case).

END IF;

END;

The calling application gets a PL/SQL exception, which it can process using the error-reporting functions

SQLCODE

and

SQLERRM

in an

OTHERS

handler. Also, it can use the pragma

EXCEPTION_INIT

to map specific error numbers returned by raise_application_error

to exceptions of its own, as the following Pro*C example shows:

EXEC SQL EXECUTE

/* Execute embedded PL/SQL block using host variables v_emp_id and v_amount, which were assigned values in the host environment. */

DECLARE null_salary EXCEPTION;

/* Map error number returned by raise_application_error to user-defined exception. */

PRAGMA EXCEPTION_INIT(null_salary, -20101);

BEGIN raise_salary(:v_emp_id, :v_amount);

EXCEPTION

WHEN null_salary THEN

INSERT INTO emp_audit VALUES (:v_emp_id, ...);

END;

END-EXEC;

This technique allows the calling application to handle error conditions in specific exception handlers.

Redeclaring Predefined Exceptions

Remember, PL/SQL declares predefined exceptions globally in package

STANDARD

, so you need not declare them yourself. Redeclaring predefined exceptions is error prone because your local declaration overrides the global declaration. For example, if you declare an exception named invalid_number

and then PL/SQL raises the predefined exception

INVALID_NUMBER

internally, a handler written for

INVALID_NUMBER

will not catch the internal exception. In such cases, you must use dot notation to specify the predefined exception, as follows:

EXCEPTION

WHEN invalid_number OR STANDARD.INVALID_NUMBER THEN

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Oracle Database PL/SQL User’s Guide and Reference

How PL/SQL Exceptions Propagate

END;

-- handle the error

How PL/SQL Exceptions Are Raised

Internal exceptions are raised implicitly by the run-time system, as are user-defined exceptions that you have associated with an Oracle error number using

EXCEPTION_INIT

. However, other user-defined exceptions must be raised explicitly by

RAISE

statements.

Raising Exceptions with the RAISE Statement

PL/SQL blocks and subprograms should raise an exception only when an error makes it undesirable or impossible to finish processing. You can place

RAISE

statements for a

given exception anywhere within the scope of that exception. In Example 10–6 , you

alert your PL/SQL block to a user-defined exception named out_of_stock

Example 10–6 Using RAISE to Force a User-Defined Exception

DECLARE

out_of_stock EXCEPTION;

number_on_hand NUMBER := 0;

BEGIN

IF number_on_hand < 1 THEN

RAISE out_of_stock; -- raise an exception that we defined

END IF;

EXCEPTION

WHEN out_of_stock THEN

-- handle the error

DBMS_OUTPUT.PUT_LINE('Encountered out-of-stock error.');

END;

You can also raise a predefined exception explicitly. That way, an exception handler

written for the predefined exception can process other errors, as Example 10–7 shows:

Example 10–7 Using RAISE to Force a Pre-Defined Exception

DECLARE

acct_type INTEGER := 7;

BEGIN

IF acct_type NOT IN (1, 2, 3) THEN

RAISE INVALID_NUMBER; -- raise predefined exception

END IF;

EXCEPTION

WHEN INVALID_NUMBER THEN

DBMS_OUTPUT.PUT_LINE('HANDLING INVALID INPUT BY ROLLING BACK.');

ROLLBACK;

END;

How PL/SQL Exceptions Propagate

When an exception is raised, if PL/SQL cannot find a handler for it in the current block or subprogram, the exception propagates. That is, the exception reproduces itself in successive enclosing blocks until a handler is found or there are no more blocks to search. If no handler is found, PL/SQL returns an unhandled exception error to the host environment.

Handling PL/SQL Errors

10-9

How PL/SQL Exceptions Propagate

Exceptions cannot propagate across remote procedure calls done through database links. A PL/SQL block cannot catch an exception raised by a remote subprogram. For

a workaround, see "Defining Your Own Error Messages: Procedure

RAISE_APPLICATION_ERROR" on page 10-7.

Figure 10–1 , Figure 10–2 , and

Figure 10–3 illustrate the basic propagation rules.

Figure 10–1 Propagation Rules: Example 1

BEGIN

IF X = 1 THEN

RAISE A;

ELSIF X = 2 THEN

RAISE B;

ELSE

RAISE C;

END IF;

...

EXCEPTION

WHEN A THEN

...

END;

Exception A is handled locally, then execution resumes in the enclosing block

EXCEPTION

WHEN B THEN

...

END;

Figure 10–2 Propagation Rules: Example 2

BEGIN

IF X = 1 THEN

RAISE A;

ELSIF X = 2 THEN

RAISE B;

ELSE

RAISE C;

END IF;

...

EXCEPTION

WHEN A THEN

...

END;

Exception B propagates to the first enclosing block with an appropriate handler

EXCEPTION

WHEN B THEN

...

END;

Exception B is handled, then control passes to the host environment

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Reraising a PL/SQL Exception

Figure 10–3 Propagation Rules: Example 3

BEGIN

IF X = 1 THEN

RAISE A;

ELSIF X = 2 THEN

RAISE B;

ELSE

RAISE C;

END IF;

...

EXCEPTION

WHEN A THEN

...

END;

EXCEPTION

WHEN B THEN

...

END;

Exception C has no handler, so an unhandled exception is returned to the host environment

An exception can propagate beyond its scope, that is, beyond the block in which it was declared, as shown in

Example 10–8 .

Example 10–8 Scope of an Exception

BEGIN

DECLARE ---------- sub-block begins

past_due EXCEPTION;

due_date DATE := trunc(SYSDATE) - 1;

todays_date DATE := trunc(SYSDATE);

BEGIN

IF due_date < todays_date THEN

RAISE past_due;

END IF;

END; ------------- sub-block ends

EXCEPTION

WHEN OTHERS THEN

ROLLBACK;

END;

Because the block that declares the exception past_due

has no handler for it, the exception propagates to the enclosing block. But the enclosing block cannot reference the name

PAST_DUE

, because the scope where it was declared no longer exists. Once the exception name is lost, only an

OTHERS

handler can catch the exception. If there is no handler for a user-defined exception, the calling application gets this error:

ORA-06510: PL/SQL: unhandled user-defined exception

Reraising a PL/SQL Exception

Sometimes, you want to reraise an exception, that is, handle it locally, then pass it to an enclosing block. For example, you might want to roll back a transaction in the current block, then log the error in an enclosing block.

To reraise an exception, use a

RAISE

statement without an exception name, which is allowed only in an exception handler:

Handling PL/SQL Errors

10-11

Handling Raised PL/SQL Exceptions

Example 10–9 Reraising a PL/SQL Exception

DECLARE

salary_too_high EXCEPTION;

current_salary NUMBER := 20000;

max_salary NUMBER := 10000;

erroneous_salary NUMBER;

BEGIN

BEGIN ---------- sub-block begins

IF current_salary > max_salary THEN

RAISE salary_too_high; -- raise the exception

END IF;

EXCEPTION

WHEN salary_too_high THEN

-- first step in handling the error

DBMS_OUTPUT.PUT_LINE('Salary ' || erroneous_salary || ' is out of range.');

DBMS_OUTPUT.PUT_LINE('Maximum salary is ' || max_salary || '.');

RAISE; -- reraise the current exception

END; ------------ sub-block ends

EXCEPTION

WHEN salary_too_high THEN

-- handle the error more thoroughly

erroneous_salary := current_salary;

current_salary := max_salary;

DBMS_OUTPUT.PUT_LINE('Revising salary from ' || erroneous_salary ||

' to ' || current_salary || '.');

END;

Handling Raised PL/SQL Exceptions

When an exception is raised, normal execution of your PL/SQL block or subprogram stops and control transfers to its exception-handling part, which is formatted as follows:

EXCEPTION

WHEN exception1 THEN -- handler for exception1 sequence_of_statements1

WHEN exception2 THEN -- another handler for exception2 sequence_of_statements2

...

WHEN OTHERS THEN -- optional handler for all other errors sequence_of_statements3

END;

To catch raised exceptions, you write exception handlers. Each handler consists of a

WHEN

clause, which specifies an exception, followed by a sequence of statements to be executed when that exception is raised. These statements complete execution of the block or subprogram; control does not return to where the exception was raised. In other words, you cannot resume processing where you left off.

The optional

OTHERS

exception handler, which is always the last handler in a block or subprogram, acts as the handler for all exceptions not named specifically. Thus, a block or subprogram can have only one

OTHERS

handler. Use of the

OTHERS

handler guarantees that no exception will go unhandled.

If you want two or more exceptions to execute the same sequence of statements, list the exception names in the

WHEN

clause, separating them by the keyword

, as follows:

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Handling Raised PL/SQL Exceptions

EXCEPTION

WHEN over_limit OR under_limit OR VALUE_ERROR THEN

-- handle the error

If any of the exceptions in the list is raised, the associated sequence of statements is executed. The keyword

OTHERS

cannot appear in the list of exception names; it must appear by itself. You can have any number of exception handlers, and each handler can associate a list of exceptions with a sequence of statements. However, an exception name can appear only once in the exception-handling part of a PL/SQL block or subprogram.

The usual scoping rules for PL/SQL variables apply, so you can reference local and global variables in an exception handler. However, when an exception is raised inside a cursor

FOR

loop, the cursor is closed implicitly before the handler is invoked.

Therefore, the values of explicit cursor attributes are not available in the handler.

Exceptions Raised in Declarations

Exceptions can be raised in declarations by faulty initialization expressions. For example, the following declaration raises an exception because the constant credit_limit

cannot store numbers larger than 999:

Example 10–10 Raising an Exception in a Declaration

DECLARE

credit_limit CONSTANT NUMBER(3) := 5000; -- raises an error

BEGIN

NULL;

EXCEPTION

WHEN OTHERS THEN

-- Cannot catch the exception. This handler is never called.

DBMS_OUTPUT.PUT_LINE('Can''t handle an exception in a declaration.');

END;

Handlers in the current block cannot catch the raised exception because an exception raised in a declaration propagates immediately to the enclosing block.

Handling Exceptions Raised in Handlers

When an exception occurs within an exception handler, that same handler cannot catch the exception. An exception raised inside a handler propagates immediately to the enclosing block, which is searched to find a handler for this new exception. From there on, the exception propagates normally. For example:

EXCEPTION

WHEN INVALID_NUMBER THEN

INSERT INTO ... -- might raise DUP_VAL_ON_INDEX

WHEN DUP_VAL_ON_INDEX THEN ... -- cannot catch the exception

END;

Branching to or from an Exception Handler

GOTO

statement can branch from an exception handler into an enclosing block.

GOTO

statement cannot branch into an exception handler, or from an exception handler into the current block.

Handling PL/SQL Errors

10-13

Handling Raised PL/SQL Exceptions

Retrieving the Error Code and Error Message: SQLCODE and SQLERRM

In an exception handler, you can use the built-in functions

SQLCODE

and

SQLERRM

to find out which error occurred and to get the associated error message. For internal exceptions,

SQLCODE

returns the number of the Oracle error. The number that

SQLCODE

returns is negative unless the Oracle error is no data found

, in which case

SQLCODE

returns +100.

SQLERRM

returns the corresponding error message. The message begins with the Oracle error code.

For user-defined exceptions,

SQLCODE

returns +1 and

SQLERRM

returns the message

User-Defined Exception

unless you used the pragma

EXCEPTION_INIT

to associate the exception name with an Oracle error number, in which case

SQLCODE returns that error number and

SQLERRM

returns the corresponding error message. The maximum length of an Oracle error message is 512 characters including the error code, nested messages, and message inserts such as table and column names.

If no exception has been raised,

SQLCODE

returns zero and

SQLERRM

returns the message:

ORA-0000: normal, successful completion

You can pass an error number to

SQLERRM

, in which case

SQLERRM

returns the message associated with that error number. Make sure you pass negative error numbers to

SQLERRM

Passing a positive number to

SQLERRM

always returns the message user-defined exception

unless you pass

+100

, in which case

SQLERRM

returns the message no data found

. Passing a zero to

SQLERRM

always returns the message normal, successful completion

You cannot use

SQLCODE

SQLERRM

directly in a SQL statement. Instead, you must assign their values to local variables, then use the variables in the SQL statement, as

shown in Example 10–11 .

Example 10–11 Displaying SQLCODE and SQLERRM

CREATE TABLE errors (code NUMBER, message VARCHAR2(64), happened TIMESTAMP);

DECLARE

name employees.last_name%TYPE;

v_code NUMBER;

v_errm VARCHAR2(64);

BEGIN

SELECT last_name INTO name FROM employees WHERE employee_id = -1;

EXCEPTION

WHEN OTHERS THEN

v_code := SQLCODE;

v_errm := SUBSTR(SQLERRM, 1 , 64);

DBMS_OUTPUT.PUT_LINE('Error code ' || v_code || ': ' || v_errm);

-- Normally we would call another procedure, declared with PRAGMA

-- AUTONOMOUS_TRANSACTION, to insert information about errors.

INSERT INTO errors VALUES (v_code, v_errm, SYSTIMESTAMP);

END;

The string function

SUBSTR

ensures that a

VALUE_ERROR

exception (for truncation) is not raised when you assign the value of

SQLERRM

to err_msg

. The functions

SQLCODE

and

SQLERRM

are especially useful in the

OTHERS

exception handler because they tell you which internal exception was raised.

When using pragma

RESTRICT_REFERENCES

to assert the purity of a stored function, you cannot specify the constraints

WNPS

and

RNPS

if the function calls

SQLCODE

SQLERRM

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Handling Raised PL/SQL Exceptions

Catching Unhandled Exceptions

Remember, if it cannot find a handler for a raised exception, PL/SQL returns an unhandled exception error to the host environment, which determines the outcome.

For example, in the Oracle Precompilers environment, any database changes made by a failed SQL statement or PL/SQL block are rolled back.

Unhandled exceptions can also affect subprograms. If you exit a subprogram successfully, PL/SQL assigns values to

OUT

parameters. However, if you exit with an unhandled exception, PL/SQL does not assign values to

OUT

parameters (unless they are

NOCOPY

parameters). Also, if a stored subprogram fails with an unhandled exception, PL/SQL does not roll back database work done by the subprogram.

You can avoid unhandled exceptions by coding an

OTHERS

handler at the topmost level of every PL/SQL program.

Tips for Handling PL/SQL Errors

In this section, you learn techniques that increase flexibility.

Continuing after an Exception Is Raised

An exception handler lets you recover from an otherwise fatal error before exiting a block. But when the handler completes, the block is terminated. You cannot return to the current block from an exception handler. In the following example, if the

SELECT

INTO

statement raises

ZERO_DIVIDE

, you cannot resume with the

INSERT

statement:

CREATE TABLE employees_temp AS

SELECT employee_id, salary, commission_pct FROM employees;

DECLARE

sal_calc NUMBER(8,2);

BEGIN

INSERT INTO employees_temp VALUES (301, 2500, 0);

SELECT salary / commission_pct INTO sal_calc FROM employees_temp

WHERE employee_id = 301;

INSERT INTO employees_temp VALUES (302, sal_calc/100, .1);

EXCEPTION

WHEN ZERO_DIVIDE THEN

NULL;

END;

You can still handle an exception for a statement, then continue with the next statement. Place the statement in its own sub-block with its own exception handlers. If an error occurs in the sub-block, a local handler can catch the exception. When the sub-block ends, the enclosing block continues to execute at the point where the sub-block ends, as shown in

Example 10–12 .

Example 10–12 Continuing After an Exception

DECLARE

sal_calc NUMBER(8,2);

BEGIN

INSERT INTO employees_temp VALUES (303, 2500, 0);

BEGIN -- sub-block begins

SELECT salary / commission_pct INTO sal_calc FROM employees_temp

WHERE employee_id = 301;

EXCEPTION

WHEN ZERO_DIVIDE THEN

Handling PL/SQL Errors

10-15

Handling Raised PL/SQL Exceptions

sal_calc := 2500;

END; -- sub-block ends

INSERT INTO employees_temp VALUES (304, sal_calc/100, .1);

EXCEPTION

WHEN ZERO_DIVIDE THEN

NULL;

END;

In this example, if the

SELECT INTO

statement raises a

ZERO_DIVIDE

exception, the local handler catches it and sets sal_calc

to 2500. Execution of the handler is complete, so the sub-block terminates, and execution continues with the

INSERT statement. See also

Example 5–38, "Collection Exceptions" on page 5-27.

You can also perform a sequence of DML operations where some might fail, and process the exceptions only after the entire operation is complete, as described in

"Handling FORALL Exceptions with the %BULK_EXCEPTIONS Attribute" on page 11-14.

Retrying a Transaction

After an exception is raised, rather than abandon your transaction, you might want to retry it. The technique is:

Encase the transaction in a sub-block.

Place the sub-block inside a loop that repeats the transaction.

Before starting the transaction, mark a savepoint. If the transaction succeeds, commit, then exit from the loop. If the transaction fails, control transfers to the exception handler, where you roll back to the savepoint undoing any changes, then try to fix the problem.

Example 10–13 , the

INSERT

statement might raise an exception because of a duplicate value in a unique column. In that case, we change the value that needs to be unique and continue with the next loop iteration. If the INSERT succeeds, we exit from the loop immediately. With this technique, you should use a

FOR

WHILE

loop to limit the number of attempts.

Example 10–13 Retrying a Transaction After an Exception

CREATE TABLE results ( res_name VARCHAR(20), res_answer VARCHAR2(3) );

CREATE UNIQUE INDEX res_name_ix ON results (res_name);

INSERT INTO results VALUES ('SMYTHE', 'YES');

INSERT INTO results VALUES ('JONES', 'NO');

DECLARE

name VARCHAR2(20) := 'SMYTHE';

answer VARCHAR2(3) := 'NO';

suffix NUMBER := 1;

BEGIN

FOR i IN 1..5 LOOP -- try 5 times

BEGIN -- sub-block begins

SAVEPOINT start_transaction; -- mark a savepoint

/* Remove rows from a table of survey results. */

DELETE FROM results WHERE res_answer = 'NO';

/* Add a survey respondent's name and answers. */

INSERT INTO results VALUES (name, answer);

-- raises DUP_VAL_ON_INDEX if two respondents have the same name

COMMIT;

EXIT;

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Oracle Database PL/SQL User’s Guide and Reference

Overview of PL/SQL Compile-Time Warnings

EXCEPTION

WHEN DUP_VAL_ON_INDEX THEN

ROLLBACK TO start_transaction; -- undo changes

suffix := suffix + 1; -- try to fix problem

name := name || TO_CHAR(suffix);

END; -- sub-block ends

END LOOP;

END;

Using Locator Variables to Identify Exception Locations

Using one exception handler for a sequence of statements, such as

INSERT

DELETE

, or

UPDATE

statements, can mask the statement that caused an error. If you need to know which statement failed, you can use a locator variable

Example 10–14 Using a Locator Variable to Identify the Location of an Exception

CREATE OR REPLACE PROCEDURE loc_var AS

stmt_no NUMBER;

name VARCHAR2(100);

BEGIN

stmt_no := 1; -- designates 1st SELECT statement

SELECT table_name INTO name FROM user_tables WHERE table_name LIKE 'ABC%';

stmt_no := 2; -- designates 2nd SELECT statement

SELECT table_name INTO name FROM user_tables WHERE table_name LIKE 'XYZ%';

EXCEPTION

WHEN NO_DATA_FOUND THEN

DBMS_OUTPUT.PUT_LINE('Table name not found in query ' || stmt_no);

END;

CALL loc_var();

Overview of PL/SQL Compile-Time Warnings

To make your programs more robust and avoid problems at run time, you can turn on checking for certain warning conditions. These conditions are not serious enough to produce an error and keep you from compiling a subprogram. They might point out something in the subprogram that produces an undefined result or might create a performance problem.

To work with PL/SQL warning messages, you use the

PLSQL_WARNINGS initialization parameter, the

DBMS_WARNING

package, and the

USER/DBA/ALL_PLSQL_OBJECT_SETTINGS

views.

PL/SQL Warning Categories

PL/SQL warning messages are divided into categories, so that you can suppress or display groups of similar warnings during compilation. The categories are:

■

SEVERE

: Messages for conditions that might cause unexpected behavior or wrong results, such as aliasing problems with parameters.

PERFORMANCE

: Messages for conditions that might cause performance problems, such as passing a

VARCHAR2

value to a

NUMBER

column in an

INSERT

statement.

Handling PL/SQL Errors

10-17

Overview of PL/SQL Compile-Time Warnings

■

INFORMATIONAL

: Messages for conditions that do not have an effect on performance or correctness, but that you might want to change to make the code more maintainable, such as unreachable code that can never be executed.

The keyword

All

is a shorthand way to refer to all warning messages.

You can also treat particular messages as errors instead of warnings. For example, if you know that the warning message

PLW-05003

represents a serious problem in your code, including

'ERROR:05003'

in the

PLSQL_WARNINGS

setting makes that condition trigger an error message (

PLS_05003

) instead of a warning message. An error message causes the compilation to fail.

Controlling PL/SQL Warning Messages

To let the database issue warning messages during PL/SQL compilation, you set the initialization parameter

PLSQL_WARNINGS

. You can enable and disable entire categories of warnings (

ALL

SEVERE

INFORMATIONAL

PERFORMANCE

), enable and disable specific message numbers, and make the database treat certain warnings as compilation errors so that those conditions must be corrected.

This parameter can be set at the system level or the session level. You can also set it for a single compilation by including it as part of the

ALTER PROCEDURE

...

COMPILE statement. You might turn on all warnings during development, turn off all warnings when deploying for production, or turn on some warnings when working on a particular subprogram where you are concerned with some aspect, such as unnecessary code or performance.

Example 10–15 Controlling the Display of PL/SQL Warnings

-- To focus on one aspect

ALTER SESSION SET PLSQL_WARNINGS='ENABLE:PERFORMANCE';

-- Recompile with extra checking

ALTER PROCEDURE loc_var COMPILE PLSQL_WARNINGS='ENABLE:PERFORMANCE'

REUSE SETTINGS;

-- To turn off all warnings

ALTER SESSION SET PLSQL_WARNINGS='DISABLE:ALL';

-- Display 'severe' warnings, don't want 'performance' warnings, and

-- want PLW-06002 warnings to produce errors that halt compilation

ALTER SESSION SET PLSQL_WARNINGS='ENABLE:SEVERE', 'DISABLE:PERFORMANCE',

'ERROR:06002';

-- For debugging during development

ALTER SESSION SET PLSQL_WARNINGS='ENABLE:ALL';

Warning messages can be issued during compilation of PL/SQL subprograms; anonymous blocks do not produce any warnings.

The settings for the

PLSQL_WARNINGS

parameter are stored along with each compiled subprogram. If you recompile the subprogram with a

CREATE OR REPLACE statement, the current settings for that session are used. If you recompile the subprogram with an

ALTER

...

COMPILE

statement, the current session setting might be used, or the original setting that was stored with the subprogram, depending on whether you include the

REUSE SETTINGS

clause in the statement. For more information, see

ALTER FUNCTION

ALTER PACKAGE

, and

ALTER PROCEDURE

Oracle Database SQL Reference.

To see any warnings generated during compilation, you use the SQL*Plus

SHOW

ERRORS

command or query the

USER_ERRORS

data dictionary view. PL/SQL warning messages all use the prefix

PLW

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Oracle Database PL/SQL User’s Guide and Reference

Overview of PL/SQL Compile-Time Warnings

Using the DBMS_WARNING Package

If you are writing a development environment that compiles PL/SQL subprograms, you can control PL/SQL warning messages by calling subprograms in the

DBMS_WARNING

package. You might also use this package when compiling a complex application, made up of several nested SQL*Plus scripts, where different warning settings apply to different subprograms. You can save the current state of the

PLSQL_WARNINGS

parameter with one call to the package, change the parameter to compile a particular set of subprograms, then restore the original parameter value.

For example,

Example 10–16

is a procedure with unnecessary code that could be removed. It could represent a mistake, or it could be intentionally hidden by a debug flag, so you might or might not want a warning message for it.

Example 10–16 Using the DBMS_WARNING Package to Display Warnings

-- When warnings disabled, the following procedure compiles with no warnings

CREATE OR REPLACE PROCEDURE unreachable_code AS

x CONSTANT BOOLEAN := TRUE;

BEGIN

IF x THEN

DBMS_OUTPUT.PUT_LINE('TRUE');

ELSE

DBMS_OUTPUT.PUT_LINE('FALSE');

END IF;

END unreachable_code;

-- enable all warning messages for this session

CALL DBMS_WARNING.set_warning_setting_string('ENABLE:ALL' ,'SESSION');

-- Check the current warning setting

SELECT DBMS_WARNING.get_warning_setting_string() FROM DUAL;

-- Recompile the procedure and a warning about unreachable code displays

ALTER PROCEDURE unreachable_code COMPILE;

SHOW ERRORS;

Example 10–16 , you could have used the following

ALTER PROCEDURE

without the call to

DBMS_WARNINGS.set_warning_setting_string

ALTER PROCEDURE unreachable_code COMPILE

PLSQL_WARNINGS = 'ENABLE:ALL' REUSE SETTINGS;

For more information, see

ALTER PROCEDURE

in Oracle Database SQL Reference,

DBMS_WARNING

package in Oracle Database PL/SQL Packages and Types Reference, and

PLW- messages in Oracle Database Error Messages

Handling PL/SQL Errors

10-19

Overview of PL/SQL Compile-Time Warnings

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Oracle Database PL/SQL User’s Guide and Reference

Tuning PL/SQL Applications for Performance

This chapter shows you how to write efficient PL/SQL code, and speed up existing code.

This chapter contains these topics:

■

Initialization Parameters for PL/SQL Compilation

■

How PL/SQL Optimizes Your Programs

Guidelines for Avoiding PL/SQL Performance Problems

Profiling and Tracing PL/SQL Programs

Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

■

Writing Computation-Intensive Programs in PL/SQL

Tuning Dynamic SQL with EXECUTE IMMEDIATE and Cursor Variables

Tuning PL/SQL Procedure Calls with the NOCOPY Compiler Hint

Compiling PL/SQL Code for Native Execution

Setting Up Transformations with Pipelined Functions

Initialization Parameters for PL/SQL Compilation

There are several Oracle initialization parameters that are used in the compilation of

PL/SQL units. These designated PL/SQL compiler parameters include

Tuning PL/SQL Applications for Performance

11-1

How PL/SQL Optimizes Your Programs

PLSQL_CCFLAGS

PLSQL_CODE_TYPE

PLSQL_DEBUG

PLSQL_NATIVE_LIBRARY_DIR

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT

PLSQL_OPTIMIZE_LEVEL

PLSQL_WARNINGS

, and

NLS_LENGTH_SEMANTICS

. For information about these initialization parameters, see Oracle Database Reference.

The values at the time of compilation of the

PLSQL_CCFLAGS

PLSQL_CODE_TYPE

PLSQL_DEBUG

PLSQL_OPTIMIZE_LEVEL

PLSQL_WARNINGS

, and

NLS_LENGTH_SEMANTICS

initialization parameters are stored with the unit's metadata. You can view information about the settings of these parameters with the

ALL_PLSQL_OBJECT_SETTINGS

view. For information, see Oracle Database Reference.

You can specify

REUSE SETTINGS

with the SQL

ALTER

statement to preserve the values stored in a unit's metadata. For information of the use of the PL/SQL compiler parameters with the

ALTER

statement, see the

ALTER FUNCTION

ALTER PACKAGE

ALTER PROCEDURE

, and

ALTER SESSION

statements in the Oracle Database SQL

Reference.

How PL/SQL Optimizes Your Programs

In Oracle releases prior to 10g, the PL/SQL compiler translated your code to machine code without applying many changes for performance. Now, PL/SQL uses an optimizing compiler that can rearrange code for better performance.

You do not need to do anything to get the benefits of this new optimizer. It is enabled by default. In rare cases, if the overhead of the optimizer makes compilation of very large applications take too long, you might lower the optimization by setting the initialization parameter

PLSQL_OPTIMIZE_LEVEL=1

instead of its default value 2. In even rarer cases, you might see a change in exception behavior, either an exception that is not raised at all, or one that is raised earlier than expected. Setting

PLSQL_OPTIMIZE_LEVEL=0

prevents the code from being rearranged at all. For information on the

PLSQL_OPTIMIZE_LEVEL

initialization parameter, see Oracle

Database Reference.

You can view information about the optimization level and other PLSQL compiler settings for your environment with the

ALL_PLSQL_OBJECT_SETTINGS

view. For information, see Oracle Database Reference.

When to Tune PL/SQL Code

The information in this chapter is especially valuable if you are responsible for:

■

Programs that do a lot of mathematical calculations. You will want to investigate the datatypes

PLS_INTEGER

BINARY_FLOAT

, and

BINARY_DOUBLE

Functions that are called from PL/SQL queries, where the functions might be executed millions of times. You will want to look at all performance features to make the function as efficient as possible, and perhaps a function-based index to precompute the results for each row and save on query time.

Programs that spend a lot of time processing

INSERT

UPDATE

, or

DELETE statements, or looping through query results. You will want to investigate the

FORALL

statement for issuing DML, and the

BULK COLLECT INTO

and

RETURNING BULK COLLECT INTO

clauses for queries.

Older code that does not take advantage of recent PL/SQL language features.

With the many performance improvements in Oracle Database 10g, any code from earlier releases is a candidate for tuning.

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Oracle Database PL/SQL User’s Guide and Reference

Guidelines for Avoiding PL/SQL Performance Problems

■

Any program that spends a lot of time doing PL/SQL processing, as opposed to issuing DDL statements like

CREATE TABLE

that are just passed directly to SQL.

You will want to investigate native compilation. Because many built-in database features use PL/SQL, you can apply this tuning feature to an entire database to improve performance in many areas, not just your own code.

Before starting any tuning effort, benchmark the current system and measure how long particular subprograms take. PL/SQL in Oracle Database 10g includes many automatic optimizations, so you might see performance improvements without doing any tuning.

Guidelines for Avoiding PL/SQL Performance Problems

When a PL/SQL-based application performs poorly, it is often due to badly written

SQL statements, poor programming practices, inattention to PL/SQL basics, or misuse of shared memory.

Avoiding CPU Overhead in PL/SQL Code

This sections discusses how you can avoid excessive CPU overhead in the PL/SQL code.

Make SQL Statements as Efficient as Possible

PL/SQL programs look relatively simple because most of the work is done by SQL statements. Slow SQL statements are the main reason for slow execution.

If SQL statements are slowing down your program:

■

Make sure you have appropriate indexes. There are different kinds of indexes for different situations. Your index strategy might be different depending on the sizes of various tables in a query, the distribution of data in each query, and the columns used in the

WHERE

clauses.

Make sure you have up-to-date statistics on all the tables, using the subprograms in the

DBMS_STATS

package.

■

Analyze the execution plans and performance of the SQL statements, using:

■

EXPLAIN PLAN

statement

■

SQL Trace facility with

TKPROF

utility

Rewrite the SQL statements if necessary. For example, query hints can avoid problems such as unnecessary full-table scans.

For more information about these methods, see Oracle Database Performance Tuning

Guide.

Some PL/SQL features also help improve the performance of SQL statements:

■

If you are running SQL statements inside a PL/SQL loop, look at the

FORALL statement as a way to replace loops of

INSERT

UPDATE

, and

DELETE

statements.

If you are looping through the result set of a query, look at the

BULK COLLECT clause of the

SELECT INTO

statement as a way to bring the entire result set into memory in a single operation.

Make Function Calls as Efficient as Possible

Badly written subprograms (for example, a slow sort or search function) can harm performance. Avoid unnecessary calls to subprograms, and optimize their code:

Tuning PL/SQL Applications for Performance

11-3

Guidelines for Avoiding PL/SQL Performance Problems

■

If a function is called within a SQL query, you can cache the function value for each row by creating a function-based index on the table in the query. The

CREATE

INDEX

statement might take a while, but queries can be much faster.

If a column is passed to a function within an SQL query, the query cannot use regular indexes on that column, and the function might be called for every row in a (potentially very large) table. Consider nesting the query so that the inner query filters the results to a small number of rows, and the outer query calls the function

only a few times as shown in Example 11–1 .

Example 11–1 Nesting a Query to Improve Performance

BEGIN

-- Inefficient, calls function for every row

FOR item IN (SELECT DISTINCT(SQRT(department_id)) col_alias FROM employees)

LOOP

DBMS_OUTPUT.PUT_LINE(item.col_alias);

END LOOP;

-- Efficient, only calls function once for each distinct value.

FOR item IN

( SELECT SQRT(department_id) col_alias FROM

( SELECT DISTINCT department_id FROM employees)

)

LOOP

DBMS_OUTPUT.PUT_LINE(item.col_alias);

END LOOP;

END;

If you use

OUT

IN OUT

parameters, PL/SQL adds some performance overhead to ensure correct behavior in case of exceptions (assigning a value to the

OUT

parameter, then exiting the subprogram because of an unhandled exception, so that the

OUT parameter keeps its original value).

If your program does not depend on

OUT

parameters keeping their values in such situations, you can add the

NOCOPY

keyword to the parameter declarations, so the parameters are declared

OUT NOCOPY

IN OUT NOCOPY

This technique can give significant speedup if you are passing back large amounts of data in

OUT

parameters, such as collections, big

VARCHAR2

values, or LOBs.

This technique also applies to member methods of object types. If these methods modify attributes of the object type, all the attributes are copied when the method ends. To avoid this overhead, you can explicitly declare the first parameter of the member method as

SELF IN OUT NOCOPY

, instead of relying on PL/SQL's implicit declaration

SELF IN OUT

. For information about design considerations for object methods, see Oracle Database Application Developer's Guide - Object-Relational Features.

■

Make Loops as Efficient as Possible

Because PL/SQL applications are often built around loops, it is important to optimize the loop itself and the code inside the loop:

To issue a series of DML statements, replace loop constructs with

FORALL statements.

To loop through a result set and store the values, use the

BULK COLLECT

clause on the query to bring the query results into memory in one operation.

If you have to loop through a result set more than once, or issue other queries as you loop through a result set, you can probably enhance the original query to give

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Oracle Database PL/SQL User’s Guide and Reference

Guidelines for Avoiding PL/SQL Performance Problems

■ you exactly the results you want. Some query operators to explore include

UNION

INTERSECT

MINUS

, and

CONNECT BY

You can also nest one query inside another (known as a subselect) to do the filtering and sorting in multiple stages. For example, instead of calling a PL/SQL function in the inner

WHERE

clause (which might call the function once for each row of the table), you can filter the result set to a small set of rows in the inner query, and call the function in the outer query.

Do Not Duplicate Built-in String Functions

PL/SQL provides many highly optimized string functions such as

REPLACE

TRANSLATE

SUBSTR

INSTR

RPAD

, and

LTRIM

. The built-in functions use low-level code that is more efficient than regular PL/SQL.

If you use PL/SQL string functions to search for regular expressions, consider using the built-in regular expression functions, such as

REGEXP_SUBSTR

■

You can search for regular expressions using the SQL operator

REGEXP_LIKE

. See

Example 6–10 on page 6-10.

■

You can test or manipulate strings using the built-in functions

REGEXP_INSTR

REGEXP_REPLACE

, and

REGEXP_SUBSTR

Oracle's regular expression features use characters like '.', '*', '^', and '$' that you might be familiar with from UNIX or Perl programming. For multi-language programming, there are also extensions such as '[:lower:]' to match a lowercase letter, instead of '[a-z]' which does not match lowercase accented letters.

Reorder Conditional Tests to Put the Least Expensive First

PL/SQL stops evaluating a logical expression as soon as the result can be determined.

This functionality is known as short-circuit evaluation. See

"Short-Circuit Evaluation" on page 2-21.

When evaluating multiple conditions separated by

AND

, put the least expensive ones first. For example, check the values of PL/SQL variables before testing function return values, because PL/SQL might be able to skip calling the functions.

Minimize Datatype Conversions

At run time, PL/SQL converts between different datatypes automatically. For example, assigning a

PLS_INTEGER

variable to a

NUMBER

variable results in a conversion because their internal representations are different.

Whenever possible, choose datatypes carefully to minimize implicit conversions. Use literals of the appropriate types, such as character literals in character expressions and decimal numbers in number expressions.

Minimizing conversions might mean changing the types of your variables, or even working backward and designing your tables with different datatypes. Or, you might convert data once, such as from an

INTEGER

column to a

PLS_INTEGER

variable, and use the PL/SQL type consistently after that. Note that the conversion from an

INTEGER

to a

PLS_INTEGER

datatype could actually improve performance because of

Tuning PL/SQL Applications for Performance

11-5

Guidelines for Avoiding PL/SQL Performance Problems the use of more efficient hardware arithmetic. See

"Use PLS_INTEGER for Integer

Arithmetic" on page 11-6.

Use PLS_INTEGER for Integer Arithmetic

When you need to declare a local integer variable, use the datatype

PLS_INTEGER

, which is the most efficient integer type.

PLS_INTEGER

values require less storage than

INTEGER

NUMBER

values, and

PLS_INTEGER

operations use hardware arithmetic.

Note that the

BINARY_INTEGER

datatype is identical to

PLS_INTEGER

The datatype

NUMBER

and its subtypes are represented in a special internal format, designed for portability and arbitrary scale and precision, not performance. Even the subtype

INTEGER

is treated as a floating-point number with nothing after the decimal point. Operations on

NUMBER

INTEGER

variables require calls to library routines.

Avoid constrained subtypes such as

INTEGER

NATURAL

NATURALN

POSITIVE

POSITIVEN

, and

SIGNTYPE

in performance-critical code. Variables of these types require extra checking at run time, each time they are used in a calculation.

Use BINARY_FLOAT and BINARY_DOUBLE for Floating-Point Arithmetic

The datatype

NUMBER

and its subtypes are represented in a special internal format, designed for portability and arbitrary scale and precision, not performance.

Operations on

NUMBER

INTEGER

variables require calls to library routines.

The

BINARY_FLOAT

and

BINARY_DOUBLE

types can use native hardware arithmetic instructions, and are more efficient for number-crunching applications such as scientific processing. They also require less space in the database.

These types do not always represent fractional values precisely, and handle rounding differently than the

NUMBER

types. These types are less suitable for financial code where accuracy is critical.

Avoiding Memory Overhead in PL/SQL Code

This sections discusses how you can avoid excessive memory overhead in the PL/SQL code.

Be Generous When Declaring Sizes for VARCHAR2 Variables

You might need to allocate large

VARCHAR2

variables when you are not sure how big an expression result will be. You can actually conserve memory by declaring

VARCHAR2

variables with large sizes, such as 32000, rather than estimating just a little on the high side, such as by specifying 256 or 1000. PL/SQL has an optimization that makes it easy to avoid overflow problems and still conserve memory. Specify a size of more than 4000 characters for the

VARCHAR2

variable; PL/SQL waits until you assign the variable, then only allocates as much storage as needed.

Group Related Subprograms into Packages

When you call a packaged subprogram for the first time, the whole package is loaded into the shared memory pool. Subsequent calls to related subprograms in the package require no disk I/O, and your code executes faster. If the package is aged out of memory, it must be reloaded if you reference it again.

You can improve performance by sizing the shared memory pool correctly. Make sure it is large enough to hold all frequently used packages but not so large that memory is wasted.

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Oracle Database PL/SQL User’s Guide and Reference

Profiling and Tracing PL/SQL Programs

Pin Packages in the Shared Memory Pool

You can pin frequently accessed packages in the shared memory pool, using the supplied package

DBMS_SHARED_POOL

. When a package is pinned, it is not aged out by the least recently used (LRU) algorithm that Oracle normally uses. The package remains in memory no matter how full the pool gets or how frequently you access the package.

For more information on the

DBMS_SHARED_POOL

package, see Oracle Database

PL/SQL Packages and Types Reference.

Improve Your Code to Avoid Compiler Warnings

The PL/SQL compiler issues warnings about things that do not make a program incorrect, but might lead to poor performance. If you receive such a warning, and the performance of this code is important, follow the suggestions in the warning and change the code to be more efficient.

Profiling and Tracing PL/SQL Programs

As you develop larger and larger PL/SQL applications, it becomes more difficult to isolate performance problems. PL/SQL provides a Profiler API to profile run-time behavior and to help you identify performance bottlenecks. PL/SQL also provides a

Trace API for tracing the execution of programs on the server. You can use Trace to trace the execution by subprogram or exception.

Using The Profiler API: Package DBMS_PROFILER

The Profiler API is implemented as PL/SQL package

DBMS_PROFILER

, which provides services for gathering and saving run-time statistics. The information is stored in database tables, which you can query later. For example, you can learn how much time was spent executing each PL/SQL line and subprogram.

To use the Profiler, you start the profiling session, run your application long enough to get adequate code coverage, flush the collected data to the database, then stop the profiling session.

The Profiler traces the execution of your program, computing the time spent at each line and in each subprogram. You can use the collected data to improve performance.

For instance, you might focus on subprograms that run slowly. For information about the

DBMS_PROFILER

subprograms, see Oracle Database PL/SQL Packages and Types

Reference.

After you have collected data with the Profiler, you can do the following:

■

Analyze the Collected Performance Data

■

Determine why more time was spent executing certain code segments or accessing certain data structures. Find the problem areas by querying the performance data.

Focus on the subprograms and packages that use up the most execution time, inspecting possible performance bottlenecks such as SQL statements, loops, and recursive functions.

Use Trace Data to Improve Performance

Use the results of your analysis to rework slow algorithms. For example, due to an exponential growth in data, you might need to replace a linear search with a binary search. Also, look for inefficiencies caused by inappropriate data structures, and, if necessary, replace those data structures.

Tuning PL/SQL Applications for Performance

11-7

Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

Using The Trace API: Package DBMS_TRACE

With large, complex applications, it becomes difficult to keep track of calls between subprograms. By tracing your code with the Trace API, you can see the order in which subprograms execute. The Trace API is implemented as PL/SQL package

DBMS_TRACE

, which provides services for tracing execution by subprogram or exception.

To use Trace, you start the tracing session, run your application, then stop the tracing session. As the program executes, trace data is collected and stored in database tables.

For information about the

DBMS_TRACE

subprograms, see Oracle Database PL/SQL

Packages and Types Reference.

Controlling the Trace

Tracing large applications can produce huge amounts of data that are difficult to manage. Before starting Trace, you can optionally limit the volume of data collected by selecting specific subprograms for trace data collection.

In addition, you can choose a tracing level. For example, you can choose to trace all subprograms and exceptions, or you can choose to trace selected subprograms and exceptions.

Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

PL/SQL sends SQL statements such as DML and queries to the SQL engine for execution, and SQL returns the result data to PL/SQL. You can minimize the performance overhead of this communication between PL/SQL and SQL by using the

PL/SQL language features known collectively as bulk SQL. The

FORALL

statement sends

INSERT

UPDATE

, or

DELETE

statements in batches, rather than one at a time.

The

BULK COLLECT

clause brings back batches of results from SQL. If the DML statement affects four or more database rows, the use of bulk SQL can improve performance considerably.

The assigning of values to PL/SQL variables in SQL statements is called binding.

PL/SQL binding operations fall into three categories:

■ in-bind

: When a PL/SQL variable or host variable is stored in the database by an

INSERT

UPDATE

statement.

■

■ out-bind

: When a database value is assigned to a PL/SQL variable or a host variable by the

RETURNING

clause of an

INSERT

UPDATE

, or

DELETE

statement.

define

: When a database value is assigned to a PL/SQL variable or a host variable by a

SELECT

FETCH

statement.

Bulk SQL uses PL/SQL collections, such as varrays or nested tables, to pass large amounts of data back and forth in a single operation. This process is known as bulk binding. If the collection has 20 elements, bulk binding lets you perform the equivalent of 20

SELECT

INSERT

UPDATE

, or

DELETE

statements using a single operation.

Queries can pass back any number of results, without requiring a

FETCH

statement for each row.

To speed up

INSERT

UPDATE

, and

DELETE

statements, enclose the SQL statement within a PL/SQL

FORALL

statement instead of a loop construct.

To speed up

SELECT

statements, include the

BULK COLLECT INTO

clause in the

SELECT

statement instead of using

INTO

11-8

Oracle Database PL/SQL User’s Guide and Reference

Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

For full details of the syntax and restrictions for these statements, see "FORALL

Statement" on page 13-56 and

"FORALL Statement" on page 13-56.

Using the FORALL Statement

The keyword

FORALL

lets you run multiple DML statements very efficiently. It can only repeat a single DML statement, unlike a general-purpose

FOR

loop. For full syntax and restrictions, see

The SQL statement can reference more than one collection, but

FORALL

only improves performance where the index value is used as a subscript.

Usually, the bounds specify a range of consecutive index numbers. If the index numbers are not consecutive, such as after you delete collection elements, you can use the

INDICES OF

VALUES OF

clause to iterate over just those index values that really exist.

The

INDICES OF

clause iterates over all of the index values in the specified collection, or only those between a lower and upper bound.

The

VALUES OF clause refers to a collection that is indexed by

BINARY_INTEGER

PLS_INTEGER

and whose elements are of type

BINARY_INTEGER

PLS_INTEGER

The

FORALL

statement iterates over the index values specified by the elements of this collection.

The

FORALL

statement in

Example 11–2

sends all three

DELETE

statements to the SQL engine at once.

Example 11–2 Issuing DELETE Statements in a Loop

CREATE TABLE employees_temp AS SELECT * FROM employees;

DECLARE

TYPE NumList IS VARRAY(20) OF NUMBER;

depts NumList := NumList(10, 30, 70); -- department numbers

BEGIN

FORALL i IN depts.FIRST..depts.LAST

DELETE FROM employees_temp WHERE department_id = depts(i);

COMMIT;

END;

Example 11–3 loads some data into PL/SQL collections. Then it inserts the collection

elements into a database table twice: first using a

FOR

loop, then using a

FORALL statement. The

FORALL

version is much faster.

Example 11–3 Issuing INSERT Statements in a Loop

CREATE TABLE parts1 (pnum INTEGER, pname VARCHAR2(15));

CREATE TABLE parts2 (pnum INTEGER, pname VARCHAR2(15));

DECLARE

TYPE NumTab IS TABLE OF parts1.pnum%TYPE INDEX BY PLS_INTEGER;

TYPE NameTab IS TABLE OF parts1.pname%TYPE INDEX BY PLS_INTEGER;

pnums NumTab;

pnames NameTab;

iterations CONSTANT PLS_INTEGER := 500;

t1 INTEGER;

t2 INTEGER;

t3 INTEGER;

BEGIN

FOR j IN 1..iterations LOOP -- load index-by tables

pnums(j) := j;

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pnames(j) := 'Part No. ' || TO_CHAR(j);

END LOOP;

t1 := DBMS_UTILITY.get_time;

FOR i IN 1..iterations LOOP -- use FOR loop

INSERT INTO parts1 VALUES (pnums(i), pnames(i));

END LOOP;

t2 := DBMS_UTILITY.get_time;

FORALL i IN 1..iterations -- use FORALL statement

INSERT INTO parts2 VALUES (pnums(i), pnames(i));

t3 := DBMS_UTILITY.get_time;

DBMS_OUTPUT.PUT_LINE('Execution Time (secs)');

DBMS_OUTPUT.PUT_LINE('---------------------');

DBMS_OUTPUT.PUT_LINE('FOR loop: ' || TO_CHAR((t2 - t1)/100));

DBMS_OUTPUT.PUT_LINE('FORALL: ' || TO_CHAR((t3 - t2)/100));

COMMIT;

END;

Executing this block should show that the loop using

FORALL

is much faster.

The bounds of the

FORALL

loop can apply to part of a collection, not necessarily all the elements, as shown in

Example 11–4

Example 11–4 Using FORALL with Part of a Collection

CREATE TABLE employees_temp AS SELECT * FROM employees;

DECLARE

TYPE NumList IS VARRAY(10) OF NUMBER;

depts NumList := NumList(5,10,20,30,50,55,57,60,70,75);

BEGIN

FORALL j IN 4..7 -- use only part of varray

DELETE FROM employees_temp WHERE department_id = depts(j);

COMMIT;

END;

You might need to delete some elements from a collection before using the collection in a

FORALL

statement. The

INDICES OF

clause processes sparse collections by iterating through only the remaining elements.

You might also want to leave the original collection alone, but process only some elements, process the elements in a different order, or process some elements more than once. Instead of copying the entire elements into new collections, which might use up substantial amounts of memory, the

VALUES OF

clause lets you set up simple collections whose elements serve as pointers to elements in the original collection.

Example 11–5 creates a collection holding some arbitrary data, a set of table names.

Deleting some of the elements makes it a sparse collection that would not work in a default

FORALL

statement. The program uses a

FORALL

statement with the

INDICES

clause to insert the data into a table. It then sets up two more collections, pointing to certain elements from the original collection. The program stores each set of names in a different database table using

FORALL

statements with the

VALUES OF

clause.

Example 11–5 Using FORALL with Non-Consecutive Index Values

-- Create empty tables to hold order details

CREATE TABLE valid_orders (cust_name VARCHAR2(32), amount NUMBER(10,2));

CREATE TABLE big_orders AS SELECT * FROM valid_orders WHERE 1 = 0;

CREATE TABLE rejected_orders AS SELECT * FROM valid_orders WHERE 1 = 0;

DECLARE

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-- Make collections to hold a set of customer names and order amounts.

SUBTYPE cust_name IS valid_orders.cust_name%TYPE;

TYPE cust_typ IS TABLe OF cust_name;

cust_tab cust_typ;

SUBTYPE order_amount IS valid_orders.amount%TYPE;

TYPE amount_typ IS TABLE OF NUMBER;

amount_tab amount_typ;

-- Make other collections to point into the CUST_TAB collection.

TYPE index_pointer_t IS TABLE OF PLS_INTEGER;

big_order_tab index_pointer_t := index_pointer_t();

rejected_order_tab index_pointer_t := index_pointer_t();

PROCEDURE setup_data IS BEGIN

-- Set up sample order data, including some invalid orders and some 'big' orders.

cust_tab := cust_typ('Company1','Company2','Company3','Company4','Company5');

amount_tab := amount_typ(5000.01, 0, 150.25, 4000.00, NULL);

END;

BEGIN

setup_data();

DBMS_OUTPUT.PUT_LINE('--- Original order data ---');

FOR i IN 1..cust_tab.LAST LOOP

DBMS_OUTPUT.PUT_LINE('Customer #' || i || ', ' || cust_tab(i) || ': $' ||

amount_tab(i));

END LOOP;

-- Delete invalid orders (where amount is null or 0).

FOR i IN 1..cust_tab.LAST LOOP

IF amount_tab(i) is null or amount_tab(i) = 0 THEN

cust_tab.delete(i);

amount_tab.delete(i);

END IF;

END LOOP;

DBMS_OUTPUT.PUT_LINE('--- Data with invalid orders deleted ---');

FOR i IN 1..cust_tab.LAST LOOP

IF cust_tab.EXISTS(i) THEN

DBMS_OUTPUT.PUT_LINE('Customer #' || i || ', ' || cust_tab(i) || ': $' ||

amount_tab(i));

END IF;

END LOOP;

-- Because the subscripts of the collections are not consecutive, use

-- FORALL...INDICES OF to iterate through the actual subscripts,

-- rather than 1..COUNT

FORALL i IN INDICES OF cust_tab

INSERT INTO valid_orders(cust_name, amount)

VALUES(cust_tab(i), amount_tab(i));

-- Now process the order data differently

-- Extract 2 subsets and store each subset in a different table

setup_data(); -- Initialize the CUST_TAB and AMOUNT_TAB collections again.

FOR i IN cust_tab.FIRST .. cust_tab.LAST LOOP

IF amount_tab(i) IS NULL OR amount_tab(i) = 0 THEN

rejected_order_tab.EXTEND; -- Add a new element to this collection

-- Record the subscript from the original collection

rejected_order_tab(rejected_order_tab.LAST) := i;

END IF;

IF amount_tab(i) > 2000 THEN

big_order_tab.EXTEND; -- Add a new element to this collection

-- Record the subscript from the original collection

big_order_tab(big_order_tab.LAST) := i;

END IF;

END LOOP;

-- Now it's easy to run one DML statement on one subset of elements,

-- and another DML statement on a different subset.

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FORALL i IN VALUES OF rejected_order_tab

INSERT INTO rejected_orders VALUES (cust_tab(i), amount_tab(i));

FORALL i IN VALUES OF big_order_tab

INSERT INTO big_orders VALUES (cust_tab(i), amount_tab(i));

COMMIT;

END;

-- Verify that the correct order details were stored

SELECT cust_name "Customer", amount "Valid order amount" FROM valid_orders;

SELECT cust_name "Customer", amount "Big order amount" FROM big_orders;

SELECT cust_name "Customer", amount "Rejected order amount" FROM rejected_orders;

How FORALL Affects Rollbacks

In a

FORALL

statement, if any execution of the SQL statement raises an unhandled exception, all database changes made during previous executions are rolled back.

However, if a raised exception is caught and handled, changes are rolled back to an implicit savepoint marked before each execution of the SQL statement. Changes made during previous executions are not rolled back. For example, suppose you create a database table that stores department numbers and job titles, as shown in

Example 11–6 . Then, you change the job titles so that they are longer. The second

UPDATE

fails because the new value is too long for the column. Because we handle the exception, the first

UPDATE

is not rolled back and we can commit that change.

Example 11–6 Using Rollbacks With FORALL

CREATE TABLE emp_temp (deptno NUMBER(2), job VARCHAR2(18));

DECLARE

TYPE NumList IS TABLE OF NUMBER;

depts NumList := NumList(10, 20, 30);

BEGIN

INSERT INTO emp_temp VALUES(10, 'Clerk');

-- Lengthening this job title causes an exception

INSERT INTO emp_temp VALUES(20, 'Bookkeeper');

INSERT INTO emp_temp VALUES(30, 'Analyst');

COMMIT;

FORALL j IN depts.FIRST..depts.LAST -- Run 3 UPDATE statements.

UPDATE emp_temp SET job = job || ' (Senior)' WHERE deptno = depts(j);

-- raises a "value too large" exception

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE('Problem in the FORALL statement.');

COMMIT; -- Commit results of successful updates.

END;

Counting Rows Affected by FORALL with the %BULK_ROWCOUNT Attribute

The cursor attributes

SQL%FOUND

SQL%ISOPEN

SQL%NOTFOUND

, and

SQL%ROWCOUNT

, return useful information about the most recently executed DML

statement. For additional description of cursor attributes, see "Implicit Cursors" on page 6-6.

The

SQL

cursor has one composite attribute,

%BULK_ROWCOUNT

, for use with the

FORALL

statement. This attribute works like an associative array:

SQL%BULK_ROWCOUNT(i)

stores the number of rows processed by the i th execution of an

INSERT

UPDATE

DELETE

statement. For example:

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Example 11–7 Using %BULK_ROWCOUNT With the FORALL Statement

CREATE TABLE emp_temp AS SELECT * FROM employees;

DECLARE

TYPE NumList IS TABLE OF NUMBER;

depts NumList := NumList(30, 50, 60);

BEGIN

FORALL j IN depts.FIRST..depts.LAST

DELETE FROM emp_temp WHERE department_id = depts(j);

-- How many rows were affected by each DELETE statement?

FOR i IN depts.FIRST..depts.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Iteration #' || i || ' deleted ' ||

SQL%BULK_ROWCOUNT(i) || ' rows.');

END LOOP;

END;

The

FORALL

statement and

%BULK_ROWCOUNT

attribute use the same subscripts. For example, if

FORALL

uses the range

5..10

, so does

%BULK_ROWCOUNT

. If the

FORALL statement uses the

INDICES OF

clause to process a sparse collection,

%BULK_ROWCOUNT

has corresponding sparse subscripts. If the

FORALL

statement uses the

VALUES OF

clause to process a subset of elements,

%BULK_ROWCOUNT

has subscripts corresponding to the values of the elements in the index collection. If the index collection contains duplicate elements, so that some DML statements are issued multiple times using the same subscript, then the corresponding elements of

%BULK_ROWCOUNT

represent the sum of all rows affected by the DML statement using that subscript. For examples on how to interpret

%BULK_ROWCOUNT

when using the

INDICES OF

and

VALUES OF

clauses, see the PL/SQL sample programs at http://www.oracle.com/technology/sample_code/tech/pl_sql/

%BULK_ROWCOUNT

is usually equal to 1 for inserts, because a typical insert operation affects only a single row. For the

INSERT ... SELECT

construct,

%BULK_ROWCOUNT might be greater than 1. For example, the

FORALL

statement in Example 11–8

inserts an arbitrary number of rows for each iteration. After each iteration,

%BULK_ROWCOUNT returns the number of items inserted.

Example 11–8 Counting Rows Affected by FORALL With %BULK_ROWCOUNT

CREATE TABLE emp_by_dept AS SELECT employee_id, department_id

FROM employees WHERE 1 = 0;

DECLARE

TYPE dept_tab IS TABLE OF departments.department_id%TYPE;

deptnums dept_tab;

BEGIN

SELECT department_id BULK COLLECT INTO deptnums FROM departments;

FORALL i IN 1..deptnums.COUNT

INSERT INTO emp_by_dept

SELECT employee_id, department_id FROM employees

WHERE department_id = deptnums(i);

FOR i IN 1..deptnums.COUNT LOOP

-- Count how many rows were inserted for each department; that is,

-- how many employees are in each department.

DBMS_OUTPUT.PUT_LINE('Dept '||deptnums(i)||': inserted '||

SQL%BULK_ROWCOUNT(i)||' records');

END LOOP;

DBMS_OUTPUT.PUT_LINE('Total records inserted: ' || SQL%ROWCOUNT);

END;

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Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

You can also use the scalar attributes

%FOUND

%NOTFOUND

, and

%ROWCOUNT

after running a

FORALL

statement. For example,

%ROWCOUNT

returns the total number of rows processed by all executions of the SQL statement.

%FOUND

and

%NOTFOUND

refer only to the last execution of the SQL statement. You can use

%BULK_ROWCOUNT

to infer their values for individual executions. For example, when

%BULK_ROWCOUNT(i)

is zero,

%FOUND

and

%NOTFOUND

are

FALSE

and

TRUE

, respectively.

Handling FORALL Exceptions with the %BULK_EXCEPTIONS Attribute

PL/SQL provides a mechanism to handle exceptions raised during the execution of a

FORALL

statement. This mechanism enables a bulk-bind operation to save information about exceptions and continue processing.

To have a bulk bind complete despite errors, add the keywords

SAVE EXCEPTIONS

to your

FORALL

statement after the bounds, before the DML statement. You should also provide an exception handler to track the exceptions that occurred during the bulk operation.

Example 11–9 shows how you can perform a number of DML operations, without

stopping if some operations encounter errors. In the example,

EXCEPTION_INIT

is used to associate the dml_errors

exception with the

ORA-24381

error. The

ORA-24381

error is raised if any exceptions are caught and saved after a bulk operation.

All exceptions raised during the execution are saved in the cursor attribute

%BULK_EXCEPTIONS

, which stores a collection of records. Each record has two fields:

■

%BULK_EXCEPTIONS(i).ERROR_INDEX

holds the iteration of the

FORALL statement during which the exception was raised.

■

%BULK_EXCEPTIONS(i).ERROR_CODE

holds the corresponding Oracle error code.

The values stored by

%BULK_EXCEPTIONS

always refer to the most recently executed

FORALL

statement. The number of exceptions is saved in

%BULK_EXCEPTIONS.COUNT

. Its subscripts range from 1 to

COUNT

The individual error messages, or any substitution arguments, are not saved, but the error message text can looked up using

ERROR_CODE

with

SQLERRM

as shown in

Example 11–9 .

You might need to work backward to determine which collection element was used in the iteration that caused an exception. For example, if you use the

INDICES OF

clause to process a sparse collection, you must step through the elements one by one to find the one corresponding to

%BULK_EXCEPTIONS(i).ERROR_INDEX

. If you use the

VALUES OF

clause to process a subset of elements, you must find the element in the index collection whose subscript matches

%BULK_EXCEPTIONS(i).ERROR_INDEX

, and then use that element's value as the subscript to find the erroneous element in the original collection. For examples showing how to find the erroneous elements when using the

INDICES OF

and

VALUES OF

clauses, see the PL/SQL sample programs at http://www.oracle.com/technology/tech/pl_sql/

If you omit the keywords

SAVE EXCEPTIONS

, execution of the

FORALL

statement stops when an exception is raised. In that case,

SQL%BULK_EXCEPTIONS.COUNT

returns 1, and

SQL%BULK_EXCEPTIONS

contains just one record. If no exception is raised during execution,

SQL%BULK_EXCEPTIONS.COUNT

returns 0.

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Example 11–9 Bulk Operation That Continues Despite Exceptions

-- create a temporary table for this example

CREATE TABLE emp_temp AS SELECT * FROM employees;

DECLARE

TYPE empid_tab IS TABLE OF employees.employee_id%TYPE;

emp_sr empid_tab;

-- create an exception handler for ORA-24381

errors NUMBER;

dml_errors EXCEPTION;

PRAGMA EXCEPTION_INIT(dml_errors, -24381);

BEGIN

SELECT employee_id BULK COLLECT INTO emp_sr FROM emp_temp

WHERE hire_date < '30-DEC-94';

-- add '_SR' to the job_id of the most senior employees

FORALL i IN emp_sr.FIRST..emp_sr.LAST SAVE EXCEPTIONS

UPDATE emp_temp SET job_id = job_id || '_SR'

WHERE emp_sr(i) = emp_temp.employee_id;

-- If any errors occurred during the FORALL SAVE EXCEPTIONS,

-- a single exception is raised when the statement completes.

EXCEPTION

WHEN dml_errors THEN -- Now we figure out what failed and why.

errors := SQL%BULK_EXCEPTIONS.COUNT;

DBMS_OUTPUT.PUT_LINE('Number of statements that failed: ' || errors);

FOR i IN 1..errors LOOP

DBMS_OUTPUT.PUT_LINE('Error #' || i || ' occurred during '||

'iteration #' || SQL%BULK_EXCEPTIONS(i).ERROR_INDEX);

DBMS_OUTPUT.PUT_LINE('Error message is ' ||

SQLERRM(-SQL%BULK_EXCEPTIONS(i).ERROR_CODE));

END LOOP;

END;

DROP TABLE emp_temp;

The output from the example is similar to:

Number of statements that failed: 2

Error #1 occurred during iteration #7

Error message is ORA-12899: value too large for column

Error #2 occurred during iteration #13

Error message is ORA-12899: value too large for column

Example 11–9

, PL/SQL raises predefined exceptions because updated values were too large to insert into the job_id

column. After the

FORALL

statement,

SQL%BULK_EXCEPTIONS.COUNT

returned 2, and the contents of

SQL%BULK_EXCEPTIONS

were (7,12899) and (13,12899).

To get the Oracle error message (which includes the code), the value of

SQL%BULK_EXCEPTIONS(i).ERROR_CODE

was negated and then passed to the error-reporting function

SQLERRM

, which expects a negative number.

Retrieving Query Results into Collections with the BULK COLLECT Clause

Using the keywords

BULK COLLECT

with a query is a very efficient way to retrieve the result set. Instead of looping through each row, you store the results in one or more collections, in a single operation. You can use these keywords in the

SELECT INTO

and

FETCH INTO

statements, and the

RETURNING INTO

clause.

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Reducing Loop Overhead for DML Statements and Queries with Bulk SQL

With the

BULK COLLECT

clause, all the variables in the

INTO

list must be collections.

The table columns can hold scalar or composite values, including object types.

Example 11–10 loads two entire database columns into nested tables:

Example 11–10 Retrieving Query Results With BULK COLLECT

DECLARE

TYPE NumTab IS TABLE OF employees.employee_id%TYPE;

TYPE NameTab IS TABLE OF employees.last_name%TYPE;

enums NumTab; -- No need to initialize the collections.

names NameTab; -- Values will be filled in by the SELECT INTO.

PROCEDURE print_results IS

BEGIN

IF enums.COUNT = 0 THEN

DBMS_OUTPUT.PUT_LINE('No results!');

ELSE

DBMS_OUTPUT.PUT_LINE('Results:');

FOR i IN enums.FIRST .. enums.LAST

LOOP

DBMS_OUTPUT.PUT_LINE(' Employee #' || enums(i) || ': ' || names(i));

END LOOP;

END IF;

END;

BEGIN

-- Retrieve data for employees with Ids greater than 1000

SELECT employee_id, last_name

BULK COLLECT INTO enums, names FROM employees WHERE employee_id > 1000;

-- The data has all been brought into memory by BULK COLLECT

-- No need to FETCH each row from the result set

print_results();

-- Retrieve approximately 20% of all rows

SELECT employee_id, last_name

BULK COLLECT INTO enums, names FROM employees SAMPLE (20);

print_results();

END;

The collections are initialized automatically. Nested tables and associative arrays are extended to hold as many elements as needed. If you use varrays, all the return values must fit in the varray's declared size. Elements are inserted starting at index 1, overwriting any existing elements.

Because the processing of the

BULK COLLECT INTO

clause is similar to a

FETCH

loop, it does not raise a

NO_DATA_FOUND

exception if no rows match the query. You must check whether the resulting nested table or varray is null, or if the resulting associative array has no elements, as shown in

Example 11–10 .

To prevent the resulting collections from expanding without limit, you can use the

LIMIT

clause to or pseudocolumn

ROWNUM

to limit the number of rows processed. You can also use the

SAMPLE

clause to retrieve a random sample of rows.

Example 11–11 Using the Pseudocolumn ROWNUM to Limit Query Results

DECLARE

TYPE SalList IS TABLE OF employees.salary%TYPE;

sals SalList;

BEGIN

-- Limit the number of rows to 50

SELECT salary BULK COLLECT INTO sals FROM employees

WHERE ROWNUM <= 50;

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-- Retrieve 10% (approximately) of the rows in the table

SELECT salary BULK COLLECT INTO sals FROM employees SAMPLE (10);

END;

You can process very large result sets by fetching a specified number of rows at a time from a cursor, as shown in the following sections.

Examples of Bulk-Fetching from a Cursor

You can fetch from a cursor into one or more collections as shown in Example 11–12 .

Example 11–12 Bulk-Fetching from a Cursor Into One or More Collections

DECLARE

TYPE NameList IS TABLE OF employees.last_name%TYPE;

TYPE SalList IS TABLE OF employees.salary%TYPE;

CURSOR c1 IS SELECT last_name, salary FROM employees WHERE salary > 10000;

names NameList;

sals SalList;

TYPE RecList IS TABLE OF c1%ROWTYPE;

recs RecList;

v_limit PLS_INTEGER := 10;

PROCEDURE print_results IS

BEGIN

IF names IS NULL OR names.COUNT = 0 THEN -- check if collections are empty

DBMS_OUTPUT.PUT_LINE('No results!');

ELSE

DBMS_OUTPUT.PUT_LINE('Results: ');

FOR i IN names.FIRST .. names.LAST

LOOP

DBMS_OUTPUT.PUT_LINE(' Employee ' || names(i) || ': $' || sals(i));

END LOOP;

END IF;

END;

BEGIN

DBMS_OUTPUT.PUT_LINE('--- Processing all results at once ---');

OPEN c1;

FETCH c1 BULK COLLECT INTO names, sals;

CLOSE c1;

print_results();

DBMS_OUTPUT.PUT_LINE('--- Processing ' || v_limit || ' rows at a time ---');

OPEN c1;

LOOP

FETCH c1 BULK COLLECT INTO names, sals LIMIT v_limit;

EXIT WHEN names.COUNT = 0;

print_results();

END LOOP;

CLOSE c1;

DBMS_OUTPUT.PUT_LINE('--- Fetching records rather than columns ---');

OPEN c1;

FETCH c1 BULK COLLECT INTO recs;

FOR i IN recs.FIRST .. recs.LAST

LOOP

-- Now all the columns from the result set come from a single record

DBMS_OUTPUT.PUT_LINE(' Employee ' || recs(i).last_name || ': $'

|| recs(i).salary);

END LOOP;

END;

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Example 11–13 shows how you can fetch from a cursor into a collection of records.

Example 11–13 Bulk-Fetching from a Cursor Into a Collection of Records

DECLARE

TYPE DeptRecTab IS TABLE OF departments%ROWTYPE;

dept_recs DeptRecTab;

CURSOR c1 IS

SELECT department_id, department_name, manager_id, location_id

FROM departments WHERE department_id > 70;

BEGIN

OPEN c1;

FETCH c1 BULK COLLECT INTO dept_recs;

END;

Limiting the Rows for a Bulk FETCH Operation with the LIMIT Clause

The optional

LIMIT

clause, allowed only in bulk

FETCH

statements, limits the number

of rows fetched from the database. In Example 11–14

, with each iteration of the loop, the

FETCH

statement fetches ten rows (or less) into index-by table empids

. The previous values are overwritten. Note the use of empids.COUNT

to determine when to exit the loop.

Example 11–14 Using LIMIT to Control the Number of Rows In a BULK COLLECT

DECLARE

TYPE numtab IS TABLE OF NUMBER INDEX BY PLS_INTEGER;

CURSOR c1 IS SELECT employee_id FROM employees WHERE department_id = 80;

empids numtab;

rows PLS_INTEGER := 10;

BEGIN

OPEN c1;

LOOP -- the following statement fetches 10 rows or less in each iteration

FETCH c1 BULK COLLECT INTO empids LIMIT rows;

EXIT WHEN empids.COUNT = 0;

-- EXIT WHEN c1%NOTFOUND; -- incorrect, can omit some data

DBMS_OUTPUT.PUT_LINE('------- Results from Each Bulk Fetch --------');

FOR i IN 1..empids.COUNT LOOP

DBMS_OUTPUT.PUT_LINE( 'Employee Id: ' || empids(i));

END LOOP;

CLOSE c1;

END;

Retrieving DML Results into a Collection with the RETURNING INTO Clause

You can use the

BULK COLLECT

clause in the

RETURNING INTO

clause of an

INSERT

UPDATE

, or

DELETE

statement:

Example 11–15 Using BULK COLLECT With the RETURNING INTO Clause

CREATE TABLE emp_temp AS SELECT * FROM employees;

DECLARE

TYPE NumList IS TABLE OF employees.employee_id%TYPE;

enums NumList;

TYPE NameList IS TABLE OF employees.last_name%TYPE;

names NameList;

BEGIN

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DELETE FROM emp_temp WHERE department_id = 30

RETURNING employee_id, last_name BULK COLLECT INTO enums, names;

DBMS_OUTPUT.PUT_LINE('Deleted ' || SQL%ROWCOUNT || ' rows:');

FOR i IN enums.FIRST .. enums.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Employee #' || enums(i) || ': ' || names(i));

END LOOP;

END;

Using FORALL and BULK COLLECT Together

You can combine the

BULK COLLECT

clause with a

FORALL

statement. The output collections are built up as the

FORALL

statement iterates.

Example 11–16

, the employee_id

value of each deleted row is stored in the collection e_ids

. The collection depts

has 3 elements, so the

FORALL

statement iterates 3 times. If each

DELETE

issued by the

FORALL

statement deletes 5 rows, then the collection e_ids

, which stores values from the deleted rows, has 15 elements when the statement completes:

Example 11–16 Using FORALL With BULK COLLECT

CREATE TABLE emp_temp AS SELECT * FROM employees;

DECLARE

TYPE NumList IS TABLE OF NUMBER;

depts NumList := NumList(10,20,30);

TYPE enum_t IS TABLE OF employees.employee_id%TYPE;

TYPE dept_t IS TABLE OF employees.department_id%TYPE;

e_ids enum_t;

d_ids dept_t;

BEGIN

FORALL j IN depts.FIRST..depts.LAST

DELETE FROM emp_temp WHERE department_id = depts(j)

RETURNING employee_id, department_id BULK COLLECT INTO e_ids, d_ids;

DBMS_OUTPUT.PUT_LINE('Deleted ' || SQL%ROWCOUNT || ' rows:');

FOR i IN e_ids.FIRST .. e_ids.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Employee #' || e_ids(i) || ' from dept #' || d_ids(i));

END LOOP;

END;

The column values returned by each execution are added to the values returned previously. If you use a

FOR

loop instead of the

FORALL

statement, the set of returned values is overwritten by each

DELETE

statement.

You cannot use the

SELECT

...

BULK COLLECT

statement in a

FORALL

statement.

Using Host Arrays with Bulk Binds

Client-side programs can use anonymous PL/SQL blocks to bulk-bind input and output host arrays. This is the most efficient way to pass collections to and from the database server.

Host arrays are declared in a host environment such as an OCI or a Pro*C program and must be prefixed with a colon to distinguish them from PL/SQL collections. In the following example, an input host array is used in a

DELETE

statement. At run time, the anonymous PL/SQL block is sent to the database server for execution.

Tuning PL/SQL Applications for Performance

11-19

Writing Computation-Intensive Programs in PL/SQL

DECLARE

...

BEGIN

-- assume that values were assigned to the host array

-- and host variables in the host environment

FORALL i IN :lower..:upper

DELETE FROM employees WHERE department_id = :depts(i);

COMMIT;

END;

Writing Computation-Intensive Programs in PL/SQL

The

BINARY_FLOAT

and

BINARY_DOUBLE

datatypes make it practical to write

PL/SQL programs to do number-crunching, for scientific applications involving floating-point calculations. These datatypes behave much like the native floating-point types on many hardware systems, with semantics derived from the IEEE-754 floating-point standard.

The way these datatypes represent decimal data make them less suitable for financial applications, where precise representation of fractional amounts is more important than pure performance.

The

PLS_INTEGER

and

BINARY_INTEGER

datatypes are PL/SQL-only datatypes that are more efficient than the SQL datatypes

NUMBER

INTEGER

for integer arithmetic.

You can use

PLS_INTEGER

BINARY_INTEGER

to write pure PL/SQL code for integer arithmetic, or convert

NUMBER

INTEGER

values to

PLS_INTEGER

BINARY_INTEGER

for manipulation by PL/SQL. Note that the

BINARY_INTEGER datatype is identical to

PLS_INTEGER

. For additional considerations, see

"Change to the BINARY_INTEGER Datatype" on page xxvii.

Within a package, you can write overloaded versions of procedures and functions that accept different numeric parameters. The math routines can be optimized for each kind of parameter (

BINARY_FLOAT

BINARY_DOUBLE

NUMBER

PLS_INTEGER

), avoiding unnecessary conversions.

The built-in math functions such as

SQRT

SIN

COS

, and so on already have fast overloaded versions that accept

BINARY_FLOAT

and

BINARY_DOUBLE

parameters.

You can speed up math-intensive code by passing variables of these types to such functions, and by calling the

TO_BINARY_FLOAT

TO_BINARY_DOUBLE

functions when passing expressions to such functions.

Tuning Dynamic SQL with EXECUTE IMMEDIATE and Cursor Variables

Some programs (a general-purpose report writer for example) must build and process a variety of SQL statements, where the exact text of the statement is unknown until run time. Such statements probably change from execution to execution. They are called dynamic SQL statements.

Formerly, to execute dynamic SQL statements, you had to use the supplied package

DBMS_SQL

. Now, within PL/SQL, you can execute any kind of dynamic SQL statement using an interface called native dynamic SQL. The main PL/SQL features involved are the

EXECUTE IMMEDIATE

statement and cursor variables (also known as

REF CURSOR s).

Native dynamic SQL code is more compact and much faster than calling the

DBMS_SQL

package. The following example declares a cursor variable, then associates it with a dynamic

SELECT

statement:

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Oracle Database PL/SQL User’s Guide and Reference

Tuning PL/SQL Procedure Calls with the NOCOPY Compiler Hint

DECLARE

TYPE EmpCurTyp IS REF CURSOR;

emp_cv EmpCurTyp;

v_ename VARCHAR2(15);

v_sal NUMBER := 1000;

table_name VARCHAR2(30) := 'employees';

BEGIN

OPEN emp_cv FOR 'SELECT last_name, salary FROM ' || table_name ||

' WHERE salary > :s' USING v_sal;

CLOSE emp_cv;

END;

For more information, see

Chapter 7, "Performing SQL Operations with Native

Dynamic SQL" .

Tuning PL/SQL Procedure Calls with the NOCOPY Compiler Hint

By default,

OUT

and

IN OUT

parameters are passed by value. The values of any

OUT

parameters are copied before the subprogram is executed. During subprogram execution, temporary variables hold the output parameter values. If the subprogram exits normally, these values are copied to the actual parameters. If the subprogram exits with an unhandled exception, the original parameters are unchanged.

When the parameters represent large data structures such as collections, records, and instances of object types, this copying slows down execution and uses up memory. In particular, this overhead applies to each call to an object method: temporary copies are made of all the attributes, so that any changes made by the method are only applied if the method exits normally.

To avoid this overhead, you can specify the

NOCOPY

hint, which allows the PL/SQL compiler to pass

OUT

and

IN OUT

parameters by reference. If the subprogram exits normally, the behavior is the same as normal. If the subprogram exits early with an exception, the values of

OUT

and

IN OUT

parameters (or object attributes) might still change. To use this technique, ensure that the subprogram handles all exceptions.

The following example asks the compiler to pass

IN OUT

parameter v_staff

by reference, to avoid copying the varray on entry to and exit from the subprogram:

DECLARE

TYPE Staff IS VARRAY(200) OF Employee;

PROCEDURE reorganize (v_staff IN OUT NOCOPY Staff) IS ...

Example 11–17 loads 25,000 records into a local nested table, which is passed to two

local procedures that do nothing. A call to the procedure that uses

NOCOPY

takes much less time.

Example 11–17 Using NOCOPY With Parameters

DECLARE

TYPE EmpTabTyp IS TABLE OF employees%ROWTYPE;

emp_tab EmpTabTyp := EmpTabTyp(NULL); -- initialize

t1 NUMBER;

t2 NUMBER;

t3 NUMBER;

PROCEDURE get_time (t OUT NUMBER) IS

BEGIN t := DBMS_UTILITY.get_time; END;

PROCEDURE do_nothing1 (tab IN OUT EmpTabTyp) IS

BEGIN NULL; END;

Tuning PL/SQL Applications for Performance

11-21

Compiling PL/SQL Code for Native Execution

PROCEDURE do_nothing2 (tab IN OUT NOCOPY EmpTabTyp) IS

BEGIN NULL; END;

BEGIN

SELECT * INTO emp_tab(1) FROM employees WHERE employee_id = 100;

emp_tab.EXTEND(49999, 1); -- copy element 1 into 2..50000

get_time(t1);

do_nothing1(emp_tab); -- pass IN OUT parameter

get_time(t2);

do_nothing2(emp_tab); -- pass IN OUT NOCOPY parameter

get_time(t3);

DBMS_OUTPUT.PUT_LINE('Call Duration (secs)');

DBMS_OUTPUT.PUT_LINE('--------------------');

DBMS_OUTPUT.PUT_LINE('Just IN OUT: ' || TO_CHAR((t2 - t1)/100.0));

DBMS_OUTPUT.PUT_LINE('With NOCOPY: ' || TO_CHAR((t3 - t2))/100.0);

END;

Restrictions on NOCOPY

The use of

NOCOPY

increases the likelihood of parameter aliasing. For more

information, see "Understanding Subprogram Parameter Aliasing" on page 8-24.

Remember,

NOCOPY

is a hint, not a directive. In the following cases, the PL/SQL compiler ignores the

NOCOPY

hint and uses the by-value parameter-passing method; no error is generated:

■

The actual parameter is an element of an associative array. This restriction does not apply if the parameter is an entire associative array.

■

The actual parameter is constrained, such as by scale or

NOT NULL

. This restriction does not apply to size-constrained character strings. This restriction does not extend to constrained elements or attributes of composite types.

The actual and formal parameters are records, one or both records were declared using

%ROWTYPE

%TYPE

, and constraints on corresponding fields in the records differ.

■

The actual and formal parameters are records, the actual parameter was declared

(implicitly) as the index of a cursor

FOR

loop, and constraints on corresponding fields in the records differ.

Passing the actual parameter requires an implicit datatype conversion.

The subprogram is called through a database link or as an external procedure.

Compiling PL/SQL Code for Native Execution

You can speed up PL/SQL procedures by compiling them into native code residing in shared libraries. The procedures are translated into C code, then compiled with your usual C compiler and linked into the Oracle process.

You can use native compilation with both the supplied Oracle packages, and procedures you write yourself. Procedures compiled this way work in all server environments, such as the shared server configuration (formerly known as multi-threaded server) and Oracle Real Application Clusters.

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Compiling PL/SQL Code for Native Execution

Before You Begin

If you are a first-time user of native PL/SQL compilation, try it first with a test database, before proceeding to a production environment.

Always back up your database before configuring the database for PL/SQL native compilation. If you find that the performance benefit is outweighed by extra compilation time, it might be faster to restore from a backup than to recompile everything in interpreted mode.

Some of the setup steps require DBA authority. You must change the values of some initialization parameters, and create a new directory on the database server, preferably near the data files for the instance. The database server also needs a C compiler; on a cluster, the compiler is needed on each node. Even if you can test out these steps yourself on a development machine, you will generally need to consult with a DBA and enlist their help to use native compilation on a production server.

Note:

The pre-requirements for using native compiled PL/SQL code are documented for each platform in the individual Oracle database installation guides. Check the software requirements section for the certified compilers for native compilation on your platform to ensure that you use a certified compiler.

Determining Whether to Use PL/SQL Native Compilation

PL/SQL native compilation provides the greatest performance gains for computation-intensive procedural operations. Examples of such operations are data warehouse applications, and applications with extensive server-side transformations of data for display. In such cases, expect speed increases of up to 30%.

Because this technique cannot do much to speed up SQL statements called from

PL/SQL, it is most effective for compute-intensive PL/SQL procedures that do not spend most of their time executing SQL. You can test to see how much performance gain you can get by enabling PL/SQL native compilation.

It takes longer to compile program units with native compilation than to use the default interpreted mode. You might turn off native compilation during the busiest parts of the development cycle, where code is being frequently recompiled.

If you have determined that there will be significant performance gains in database operations using PL/SQL native compilation, Oracle Corporation recommends that you compile the entire database using the

NATIVE

setting. Compiling all the PL/SQL code in the database means you see the speedup in your own code, and in calls to all the built-in PL/SQL packages.

If interpreted compilation is required for your environment, you can compile all the

PL/SQL units to

INTERPRETED

. For example, if you import an entire database that

Tuning PL/SQL Applications for Performance

11-23

Compiling PL/SQL Code for Native Execution includes

NATIVE

PL/SQL units into an environment where a C compiler is unavailable.

To convert an entire database to

NATIVE

INTERPRETED

compilation, see

"Modifying the Entire Database for PL/SQL Native or Interpreted Compilation" on page 11-29.

How PL/SQL Native Compilation Works

If you do not use native compilation, each PL/SQL program unit is compiled into an intermediate form, machine-readable code (m-code). The m-code is stored in the database dictionary and interpreted at run time. With PL/SQL native compilation, the

PL/SQL statements are turned into C code that bypasses all the runtime interpretation, giving faster runtime performance.

PLSQL_

initialization parameters set up the environment for PL/SQL native

compilation, as described in "Setting up Initialization Parameters for PL/SQL Native

Compilation" on page 11-25.

PL/SQL uses the command file

$ORACLE_HOME/plsql/spnc_commands

, and the supported operating system C compiler and linker, to compile and link the resulting C code into shared libraries. See

"The spnc_commands File" on page 11-25.

The shared libraries are stored inside the data dictionary, so that they can be backed up automatically and are protected from being deleted. These shared library files are copied to the file system and are loaded and run when the PL/SQL subprogram is invoked. If the files are deleted from the file system while the database is shut down, or if you change the directory that holds the libraries, they are extracted again automatically.

Although PL/SQL program units that just call SQL statements might see little or no speedup, natively compiled PL/SQL is always at least as fast as the corresponding interpreted code. The compiled code makes the same library calls as the interpreted code would, so its behavior is exactly the same.

Dependencies, Invalidation and Revalidation

After the procedures are compiled and turned into shared libraries, they are automatically linked into the Oracle process. You do not need to restart the database, or move the shared libraries to a different location. You can call back and forth between stored procedures, whether they are all interpreted, all compiled for native execution, or a mixture of both.

Recompilation is automatic with invalidated PL/SQL modules. For example, if an object on which a natively compiled PL/SQL subprogram depends changes, the subprogram is invalidated. The next time the same subprogram is called, the database recompiles the subprogram automatically. Because the

PLSQL_CODE_TYPE

setting is stored inside the library unit for each subprogram, the automatic recompilation uses this stored setting for code type.

The stored settings are only used when recompiling as part of revalidation. If a

PL/SQL subprogram is explicitly compiled through the SQL commands

CREATE OR

REPLACE

ALTER...COMPILE

, the current session setting is used. See also

"Initialization Parameters for PL/SQL Compilation" on page 11-1.

The generated shared libraries are stored in the database, in the

SYSTEM

tablespace.

The first time a natively compiled procedure is executed, the corresponding shared library is copied from the database to the directory specified by the initialization parameter

PLSQL_NATIVE_LIBRARY_DIR

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Oracle Database PL/SQL User’s Guide and Reference

Compiling PL/SQL Code for Native Execution

Real Application Clusters and PL/SQL Native Compilation

Because any node might need to compile a PL/SQL subprogram, each node in the cluster needs a C compiler and correct settings and paths in the

$ORACLE_HOME/plsql/spnc_commands

file.

When you use PLSQL native compilation in a Real Application Clusters (RAC) environment, the original copies of the shared library files are stored in the databases, and these files are automatically propagated to all nodes in the cluster. You do not need to do any copying of libraries for this feature to work.

Check that all nodes of a RAC cluster use the same settings for the initialization parameters that control PL/SQL native compilation. Make sure the path specified in

PLSQL_NATIVE_LIBRARY_DIR

where the shared libraries are placed is created identically on all nodes that are part of the cluster.

■

Limitations of Native Compilation

The following are some limitations of native compilation:

Debugging tools for PL/SQL do not handle procedures compiled for native execution.

When many procedures and packages (typically, over 15000) are compiled for native execution, the large number of shared objects in a single directory might affect system performance. See

"Setting Up PL/SQL Native Library

Subdirectories" on page 11-27 for a workaround.

The spnc_commands File

The spnc_commands

file, in the

$ORACLE_HOME/plsql

directory, contains the templates for the commands to compile and link each program. Some special names such as

%(src)

are predefined, and are replaced by the corresponding filename. The variable

$(ORACLE_HOME)

is replaced by the location of the Oracle home directory.

Comment lines start with a

character. The file contains comments that explain all the special notation.

The spnc_commands

file contains a predefined path for the default C compiler, depending on the particular operating system. A specific compiler is supported on each operating system. Only one compiler can be used to compile the PL/SQL modules; do not compile PL/SQL modules in a database with different compilers.

You can view spnc_commands

file to confirm that the command templates are correct. You should not need to change this file unless the system administrator has installed the C compiler in another location or you want to use a different supported C compiler. Additional information can be found in the Oracle database installation guide for your platform and by searching for spnc_commands

on Oracle Metalink at http://metalink.oracle.com

Setting up Initialization Parameters for PL/SQL Native Compilation

This section describes the initialization parameters that are used to set PL/SQL native compilation.

■

PLSQL_NATIVE_LIBRARY_DIR

■

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT

■

PLSQL_CODE_TYPE

To check the settings of these parameters, enter the following in SQL*Plus:

Tuning PL/SQL Applications for Performance

11-25

Compiling PL/SQL Code for Native Execution

SHOW PARAMETERS PLSQL

PLSQL_NATIVE_LIBRARY_DIR Initialization Parameter

This is a required system-level only parameter that specifies the full path and directory name of the location of the shared libraries that contain natively compiled PL/SQL code. The value must be explicit and point to an existing, accessible directory; the path cannot contain a variable such as

ORACLE_HOME

. Use the

ALTER SYSTEM

command or update the initialization file to set the parameter value.

For example, if the path to the PL/SQL native library directory is

/oracle/oradata/db1/natlib

, then the setting in the initialization file is:

PLSQL_NATIVE_LIBRARY_DIR='/oracle/oradata/db1/natlib'

In accordance with optimal flexible architecture (OFA) rules, Oracle Corporation recommends that you create the shared library directory as a subdirectory where the data files are located. For security reasons, only the users oracle

and root

should have write privileges for this directory.

If using a Real Applications Cluster environment, see

"Real Application Clusters and

PL/SQL Native Compilation" on page 11-25. For details about the

PLSQL_NATIVE_LIBRARY_DIR

initialization parameter, see Oracle Database Reference.

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT Initialization Parameter

This is an optional system-level only parameter that specifies the number of subdirectories in the directory that is specified by the parameter

PLSQL_NATIVE_LIBRARY_DIR

. Use the

ALTER SYSTEM

command or update the initialization file to set the parameter value.

For example, if you want to set the parameter for 1,000 subdirectories, then the setting in the initialization parameter file is:

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT=1000;

Set this parameter if the number of natively compiled program units is very large. See

"Setting Up PL/SQL Native Library Subdirectories" on page 11-27.

For details about the

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT

initialization parameter, see Oracle Database Reference.

PLSQL_CODE_TYPE Initialization Parameter

The

PLSQL_CODE_TYPE

initialization parameter determines whether PL/SQL code is natively compiled or interpreted. The default setting is

INTERPRETED

. To enable

PL/SQL native compilation, set the value of

PLSQL_CODE_TYPE

NATIVE

The parameter can be set at the system, session level, or for a specific PL/SQL module.

Use the

ALTER SYSTEM

command,

ALTER SESSION

command, or update the initialization file to set the parameter value. If you compile the whole database as

NATIVE

, Oracle Corporation recommends that you set

PLSQL_CODE_TYPE

at the system level.

The following SQL*Plus syntax sets the parameter at the session level:

ALTER SESSION SET PLSQL_CODE_TYPE='NATIVE';

ALTER SESSION SET PLSQL_CODE_TYPE='INTERPRETED';

You can also use the

PLSQL_CODE_TYPE = NATIVE

clause with the

ALTER

COMPILE

statement for a specific PL/SQL module, as shown in Example 11–18 on page 11-28.

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Oracle Database PL/SQL User’s Guide and Reference

Compiling PL/SQL Code for Native Execution

This affects only the specified module without changing the initialization parameter for the entire session. Note that a package specification and its body do not need to be compiled with the same setting for native compilation.

For details about the

PLSQL_CODE_TYPE

initialization parameter, see Oracle Database

Reference.

Setting Up PL/SQL Native Library Subdirectories

By default, PL/SQL program units are kept in one directory. However, if the number of program units is very large, then the operating system might have difficulty handling a large of files in one directory. To avoid this problem, Oracle Corporation recommends that you spread the PL/SQL program units in subdirectories under the directory specified by the

PLSQL_NATIVE_LIBRARY_DIR

initialization parameter.

If you have an existing database that you will migrate to the new installation, or if you have set up a test database, use the following SQL query to determine how many

PL/SQL program units you are using:

SELECT COUNT (*) from DBA_PLSQL_OBJECT_SETTINGS

If you are going to exclude any units, such as packages, use the previous query with:

WHERE TYPE NOT IN ('TYPE', 'PACKAGE')

If you need to set up PL/SQL native library subdirectories, first create subdirectories sequentially in the form of d0, d1, d2, d3...dx, where x is the total number of directories. Oracle Corporation recommends that you use a script for this task. For example, you might run a PL/SQL block like the following, save its output to a file, then run that file as a shell script:

SPOOL make_dirs

BEGIN

FOR j IN 0..1000 -- change to the number of directories needed

LOOP

DBMS_OUTPUT.PUT_LINE ( 'mkdir d' || TO_CHAR(j) );

END LOOP;

END;

SPOOL OFF

Next, set the

PLSQL_NATIVE_LIBARY_SUBDIR_COUNT

initialization parameter to the number of subdirectories you have created. For example, if you created 1000 subdirectories, you can use SQL*Plus to enter the following SQL statement:

ALTER SYSTEM SET PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT=1000;

See

"PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT Initialization Parameter" on page 11-26.

Setting Up and Testing PL/SQL Native Compilation

To set up and test one or more subprograms through native compilation:

Set up the necessary initialization parameter. See

"Setting up Initialization

Parameters for PL/SQL Native Compilation" on page 11-25.

Compile one or more subprograms, using one of these methods:

■

Use

CREATE OR REPLACE

to create or recompile the subprogram.

Tuning PL/SQL Applications for Performance

11-27

Compiling PL/SQL Code for Native Execution

■

Use the

ALTER PROCEDURE

ALTER FUNCTION

, or

ALTER PACKAGE command with the

COMPILE

option to recompile a specific subprogram or

entire package, as shown in Example 11–18

Drop the subprogram and create it again.

Run one of the SQL*Plus scripts that creates a set of Oracle-supplied packages.

■

Create a database using a preconfigured initialization file with

PLSQL_CODE_TYPE=NATIVE

. During database creation, the utlirp

script is run to compile all the Oracle-supplied packages.

Example 11–18 illustrates the process of altering and testing a procedure using

native compilation. The procedure is immediately available to call, and runs as a shared library directly within the Oracle process. If any errors occur during compilation, you can see them using the

USER_ERRORS

view or the

SHOW

ERRORS

command in SQL*Plus.

Example 11–18 Compiling a PL/SQL Procedure for Native Execution

-- PLSQL_NATIVE_LIBRARY_DIR must be set to an existing, accessible directory

SET SERVEROUTPUT ON FORMAT WRAPPED

CREATE OR REPLACE PROCEDURE hello_native AS

BEGIN

DBMS_OUTPUT.PUT_LINE('Hello world. Today is ' || TO_CHAR(SYSDATE) || '.');

END hello_native;

ALTER PROCEDURE hello_native COMPILE PLSQL_CODE_TYPE=NATIVE REUSE SETTINGS;

SHOW ERRORS

-- check for a file HELLO_NATIVE... in the PLSQL_NATIVE_LIBRARY_DIR directory

CALL hello_native();

To be sure that the process worked, you can query the data dictionary to see that a procedure is compiled for native execution. To check whether an existing procedure is compiled for native execution or not, you can query the

ALL_PLSQL_OBJECT_SETTINGS

view. The

PLSQL_CODE_TYPE

column has a value of

NATIVE

for procedures that are compiled for native execution, and

INTERPRETED

otherwise. For information, see Oracle Database Reference.

For example, to check the status of the procedure hello_native

, use the query in

Example 11–19 .

Example 11–19 Checking plsql_code_type For a Compiled Procedure

SELECT PLSQL_CODE_TYPE FROM USER_PLSQL_OBJECT_SETTINGS

WHERE NAME = 'HELLO_NATIVE';

Setting Up a New Database for PL/SQL Native Compilation

Use the procedures in this section to set up an new database for PL/SQL native compilation. The performance benefits apply to all the built-in PL/SQL packages, which are used for many database operations. If using a Real Applications Cluster

environment, see "Real Application Clusters and PL/SQL Native Compilation" on page 11-25.

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Oracle Database PL/SQL User’s Guide and Reference

Compiling PL/SQL Code for Native Execution

Check that spnc_commands

file has the correct command templates. Contact your system administrator to ensure that you have the required C compiler on your operating system. See

"The spnc_commands File" on page 11-25.

Ensure that the PL/SQL native library directory is created for each Oracle database. See

"PLSQL_NATIVE_LIBRARY_DIR Initialization Parameter" on page 11-26.

■

You must set up PL/SQL libraries for each Oracle database. Shared libraries

(

.so

and

.dll

files) are logically connected to the database. They cannot be shared between databases. If you set up PL/SQL libraries to be shared, the databases will be corrupted.

Create a directory in a secure place, in accordance with OFA rules, to prevent

.so

and

.dll

files from unauthorized access.

Ensure that the compiler executables used for PL/SQL native compilation are writable only by a properly secured user.

■

Ensure that the original copies of the shared libraries are stored inside the database, so they are backed up automatically with the database.

Set up the necessary initialization parameters. See

"Setting up Initialization

Parameters for PL/SQL Native Compilation" on page 11-25.

If you use Database Configuration Assistant, use it to set the initialization parameters required for PL/SQL native compilation. Make sure that you set

PLSQL_NATIVE_LIBRARY_DIR

to an accessible directory and

PLSQL_CODE_TYPE

NATIVE

Modifying the Entire Database for PL/SQL Native or Interpreted Compilation

You can recompile all PL/SQL modules in an existing database to

NATIVE

INTERPRETED

, using the dbmsupgnv.sql

and dbmsupgin.sql

scripts respectively during the process described in this section. Before making the conversion, review

"Determining Whether to Use PL/SQL Native Compilation" on page 11-23.

During the conversion to native compilation,

TYPE

specifications are not recompiled by dbmsupgnv.sql

NATIVE

because these specifications do not contain executable code.

Package specifications seldom contain executable code so the runtime benefits of compiling to NATIVE are not measurable. You can use the

TRUE

command line parameter with the dbmsupgnv.sql

script to exclude package specs from recompilation to

NATIVE

, saving time in the conversion process.

When converting to interpreted compilation, the dbmsupgin.sql

script does not accept any parameters and does not exclude any PL/SQL units.

Note:

The following procedure describes the conversion to native compilation. If you need to recompile all PL/SQL modules to interpreted compilation, make these changes in the steps.

■

Skip the first step.

Set the

PLSQL_CODE_TYPE

initialization parameter to

INTERPRETED

rather than

NATIVE

Substitute dbmsupgin.sql

for the dbmsupgnv

.sql script.

Tuning PL/SQL Applications for Performance

11-29

Compiling PL/SQL Code for Native Execution

Ensure that following are properly configured to support native compilation:

■

A supported C compiler is installed in the database environment and that the spnc_commands

file has the correct command templates for this compiler.

■

The

PLSQL_NATIVE_LIBRARY_DIR

is set. See

"PLSQL_NATIVE_LIBRARY_DIR Initialization Parameter" on page 11-26.

The

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT

is set correctly for the number of natively compiled units after conversion. See

"PLSQL_NATIVE_LIBRARY_DIR Initialization Parameter" on page 11-26 and

"Setting Up PL/SQL Native Library Subdirectories" on page 11-27.

A test PL/SQL unit can be compiled as in Example 11–18 on page 11-28. For

example:

ALTER PROCEDURE my_proc COMPILE PLSQL_CODE_TYPE=NATIVE

REUSE SETTINGS;

Shut down application services, the listener, and the database.

■

Shut down all of the Application services including the Forms Processes, Web

Servers, Reports Servers, and Concurrent Manager Servers. After shutting down all of the Application services, ensure that all of the connections to the database have been terminated.

■

Shut down the TNS listener of the database to ensure that no new connections are made.

Shut down the database in normal or immediate mode as the user

SYS

. See

"Starting Up and Shutting Down" in the Oracle Database Administrator's Guide.

Set

PLSQL_CODE_TYPE

NATIVE

in the initialization parameter file. If the database is using a server parameter file, then set this after the database has started. See

"PLSQL_CODE_TYPE Initialization Parameter" on page 11-26.

The value of

PLSQL_CODE_TYPE

does not affect the conversion of the PL/SQL units in these steps. However, it does affect all subsequently compiled units and it should be explicitly set to the compilation type that you want.

Start up the database in upgrade mode, using the

UPGRADE

option. For information on SQL*Plus

STARTUP

, see the SQL*Plus User's Guide and Reference.

Execute the following code to list the invalid PL/SQL units. You can save the output of the query for future reference with the SQL

SPOOL

command.

Example 11–20 Checking for Invalid PL/SQL Units

REM To save the output of the query to a file:

SPOOL pre_update_invalid.log

SELECT o.OWNER, o.OBJECT_NAME, o.OBJECT_TYPE

FROM DBA_OBJECTS o, DBA_PLSQL_OBJECT_SETTINGS s

WHERE o.OBJECT_NAME = s.NAME AND o.STATUS='INVALID';

REM To stop spooling the output:

SPOOL OFF

If any Oracle supplied units are invalid, try to validate them. For example:

ALTER PACKAGE OLAPSYS.DBMS_AWM COMPILE BODY REUSE SETTINGS;

See

ALTER FUNCTION

ALTER PACKAGE

, and

ALTER PROCEDURE

, in the Oracle

Database SQL Reference.If the units cannot be validated, save the spooled log for future resolution and continue.

Execute the following query to determine how many objects are compiled

NATIVE and

INTERPRETED

. Use the SQL

SPOOL

command if you want to save the output.

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Example 11–21 Checking for PLSQL Compilation Type

SELECT TYPE, PLSQL_CODE_TYPE, COUNT(*) FROM DBA_PLSQL_OBJECT_SETTINGS

WHERE PLSQL_CODE_TYPE IS NOT NULL

GROUP BY TYPE, PLSQL_CODE_TYPE

ORDER BY TYPE, PLSQL_CODE_TYPE;

Any objects with a

NULL plsql_code_type

are special internal objects and can be ignored.

Run the

$ORACLE_HOME/rdbms/admin/dbmsupgnv.sql

script as the user

SYS to update the plsql_code_type

setting to

NATIVE

in the dictionary tables for all

PL/SQL units. This process also invalidates the units. Use

TRUE

with the script to exclude package specifications;

FALSE

to include the package specifications.

This update must be done when the database is in

UPGRADE

mode. The script is guaranteed to complete successfully or rollback all the changes.

Shut down the database and restart in

NORMAL

mode.

Before you run the utlrp.sql

script, Oracle recommends that no other sessions are connected to avoid possible problems. You can ensure this with:

ALTER SYSTEM ENABLE RESTRICTED SESSION;

10.

Run the

$ORACLE_HOME/rdbms/admin/utlrp.sql

script as the user

SYS

. This script recompiles all the PL/SQL modules using a default degree of parellelism.

See the comments in the script for information on setting the degree explicitly.

If for any reason the script is abnormally terminated, rerun the utlrp.sql

script to recompile any remaining invalid PL/SQL modules.

11.

After the compilation completes successfully, verify that there are no new invalid

PL/SQL units using the query in

Example 11–20

. You can spool the output of the query to the post_upgrade_invalid.log

file and compare the contents with the pre_upgrade_invalid.log

file, if it was created previously.

12.

Re-execute the query in

Example 11–21

. If recompiling with dbmsupgnv.sql

, confirm that all PL/SQL units, except

TYPE

specifications and package specifications if excluded, are

NATIVE

. If recompiling with dbmsupgin.sql

, confirm that all PL/SQL units are

INTERPRETED

13.

Disable the restricted session mode for the database, then start the services that you previously shut down. To disable restricted session mode:

ALTER SYSTEM DISABLE RESTRICTED SESSION;

Setting Up Transformations with Pipelined Functions

This section describes how to chain together special kinds of functions known as pipelined table functions. These functions are used in situations such as data warehousing to apply multiple transformations to data.

Tuning PL/SQL Applications for Performance

11-31

Setting Up Transformations with Pipelined Functions

Overview of Pipelined Table Functions

Pipelined table functions are functions that produce a collection of rows (either a nested table or a varray) that can be queried like a physical database table or assigned to a PL/SQL collection variable. You can use a table function in place of the name of a database table in the

FROM

clause of a query or in place of a column name in the

SELECT

list of a query.

A table function can take a collection of rows as input. An input collection parameter can be either a collection type (such as a

VARRAY

or a PL/SQL table) or a

REF

CURSOR

Execution of a table function can be parallelized, and returned rows can be streamed directly to the next process without intermediate staging. Rows from a collection returned by a table function can also be pipelined, that is, iteratively returned as they are produced instead of in a batch after all processing of the table function's input is completed.

Streaming, pipelining, and parallel execution of table functions can improve performance:

■

By enabling multi-threaded, concurrent execution of table functions

By eliminating intermediate staging between processes

■

By improving query response time: With non-pipelined table functions, the entire collection returned by a table function must be constructed and returned to the server before the query can return a single result row. Pipelining enables rows to be returned iteratively, as they are produced. This also reduces the memory that a table function requires, as the object cache does not need to materialize the entire collection.

By iteratively providing result rows from the collection returned by a table function as the rows are produced instead of waiting until the entire collection is staged in tables or memory and then returning the entire collection.

Writing a Pipelined Table Function

You declare a pipelined table function by specifying the

PIPELINED

keyword.

Pipelined functions can be defined at the schema level with

CREATE FUNCTION

or in a package. The

PIPELINED

keyword indicates that the function returns rows iteratively.

The return type of the pipelined table function must be a supported collection type, such as a nested table or a varray. This collection type can be declared at the schema level or inside a package. Inside the function, you return individual elements of the collection type. The elements of the collection type must be supported SQL datatypes, such as

NUMBER

and

VARCHAR2

. PL/SQL datatypes, such as

PLS_INTEGER

and

BOOLEAN

, are not supported as collection elements in a pipelined function.

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Example 11–22 shows how to assign the result of a pipelined table function to a

PL/SQL collection variable and use the function in a

SELECT

statement.

Example 11–22 Assigning the Result of a Table Function

CREATE PACKAGE pkg1 AS

TYPE numset_t IS TABLE OF NUMBER;

FUNCTION f1(x NUMBER) RETURN numset_t PIPELINED;

END pkg1;

CREATE PACKAGE BODY pkg1 AS

-- FUNCTION f1 returns a collection of elements (1,2,3,... x)

FUNCTION f1(x NUMBER) RETURN numset_t PIPELINED IS

BEGIN

FOR i IN 1..x LOOP

PIPE ROW(i);

END LOOP;

RETURN;

END;

END pkg1;

-- pipelined function is used in FROM clause of SELECT statement

SELECT * FROM TABLE(pkg1.f1(5));

Using Pipelined Table Functions for Transformations

A pipelined table function can accept any argument that regular functions accept. A table function that accepts a

REF CURSOR

as an argument can serve as a transformation function. That is, it can use the

REF CURSOR

to fetch the input rows, perform some transformation on them, and then pipeline the results out.

Example 11–23

, the f_trans

function converts a row of the employees

table into two rows.

Example 11–23 Using a Pipelined Table Function For a Transformation

-- Define the ref cursor types and function

CREATE OR REPLACE PACKAGE refcur_pkg IS

TYPE refcur_t IS REF CURSOR RETURN employees%ROWTYPE;

TYPE outrec_typ IS RECORD (

var_num NUMBER(6),

var_char1 VARCHAR2(30),

var_char2 VARCHAR2(30));

TYPE outrecset IS TABLE OF outrec_typ;

FUNCTION f_trans(p refcur_t)

RETURN outrecset PIPELINED;

END refcur_pkg;

CREATE OR REPLACE PACKAGE BODY refcur_pkg IS

FUNCTION f_trans(p refcur_t)

RETURN outrecset PIPELINED IS

out_rec outrec_typ;

in_rec p%ROWTYPE;

BEGIN

LOOP

FETCH p INTO in_rec;

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11-33

Setting Up Transformations with Pipelined Functions

EXIT WHEN p%NOTFOUND;

-- first row

out_rec.var_num := in_rec.employee_id;

out_rec.var_char1 := in_rec.first_name;

out_rec.var_char2 := in_rec.last_name;

PIPE ROW(out_rec);

-- second row

out_rec.var_char1 := in_rec.email;

out_rec.var_char2 := in_rec.phone_number;

PIPE ROW(out_rec);

END LOOP;

CLOSE p;

RETURN;

END;

END refcur_pkg;

-- SELECT query using the f_transc table function

SELECT * FROM TABLE(

refcur_pkg.f_trans(CURSOR(SELECT * FROM employees WHERE department_id = 60)));

In the preceding query, the pipelined table function f_trans

fetches rows from the

CURSOR

subquery

SELECT * FROM employees ...

, performs the transformation, and pipelines the results back to the user as a table. The function produces two output rows (collection elements) for each input row.

Note that when a

CURSOR

subquery is passed from SQL to a

REF CURSOR

function

argument as in Example 11–23

, the referenced cursor is already open when the function begins executing.

Returning Results from Pipelined Table Functions

In PL/SQL, the

PIPE ROW

statement causes a pipelined table function to pipe a row and continue processing. The statement enables a PL/SQL table function to return rows as soon as they are produced. For performance, the PL/SQL runtime system provides the rows to the consumer in batches.

Example 11–23

, the

PIPE ROW(out_rec)

statement pipelines data out of the

PL/SQL table function. out_rec

is a record, and its type matches the type of an element of the output collection.

The

PIPE ROW

statement may be used only in the body of pipelined table functions; an error is raised if it is used anywhere else. The

PIPE ROW

statement can be omitted for a pipelined table function that returns no rows.

A pipelined table function may have a

RETURN

statement that does not return a value.

The

RETURN

statement transfers the control back to the consumer and ensures that the next fetch gets a

NO_DATA_FOUND

exception.

Because table functions pass control back and forth to a calling routine as rows are produced, there is a restriction on combining table functions and

PRAGMA

AUTONOMOUS_TRANSACTION

. If a table function is part of an autonomous transaction, it must

COMMIT

ROLLBACK

before each

PIPE ROW

statement, to avoid an error in the calling subprogram.

Oracle has three special SQL datatypes that enable you to dynamically encapsulate and access type descriptions, data instances, and sets of data instances of any other

SQL type, including object and collection types. You can also use these three special types to create anonymous (that is, unnamed) types, including anonymous collection types. The types are

SYS.ANYTYPE

SYS.ANYDATA

, and

SYS.ANYDATASET

. The

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Setting Up Transformations with Pipelined Functions

SYS.ANYDATA

type can be useful in some situations as a return value from table functions.

Pipelining Data Between PL/SQL Table Functions

With serial execution, results are pipelined from one PL/SQL table function to another using an approach similar to co-routine execution. For example, the following statement pipelines results from function g

to function f

SELECT * FROM TABLE(f(CURSOR(SELECT * FROM TABLE(g()))));

Parallel execution works similarly except that each function executes in a different process (or set of processes).

Optimizing Multiple Calls to Pipelined Table Functions

Multiple invocations of a pipelined table function, either within the same query or in separate queries result in multiple executions of the underlying implementation. By default, there is no buffering or reuse of rows. For example:

SELECT * FROM TABLE(f(...)) t1, TABLE(f(...)) t2

WHERE t1.id = t2.id;

SELECT * FROM TABLE(f());

If the function always produces the same result value for each combination of values passed in, you can declare the function

DETERMINISTIC

, and Oracle automatically buffers rows for it. If the function is not really deterministic, results are unpredictable.

Fetching from the Results of Pipelined Table Functions

PL/SQL cursors and ref cursors can be defined for queries over table functions. For example:

OPEN c FOR SELECT * FROM TABLE(f(...));

Cursors over table functions have the same fetch semantics as ordinary cursors.

REF

CURSOR

assignments based on table functions do not have any special semantics.

However, the SQL optimizer will not optimize across PL/SQL statements. For example:

DECLARE r SYS_REFCURSOR;

BEGIN

OPEN r FOR SELECT *

FROM TABLE(f(CURSOR(SELECT * FROM tab)));

SELECT * BULK COLLECT INTO rec_tab FROM TABLE(g(r));

END;

/ does not execute as well as:

SELECT * FROM TABLE(g(CURSOR(SELECT * FROM

TABLE(f(CURSOR(SELECT * FROM tab))))));

Tuning PL/SQL Applications for Performance

11-35

Setting Up Transformations with Pipelined Functions

This is so even ignoring the overhead associated with executing two SQL statements and assuming that the results can be pipelined between the two statements.

Passing Data with Cursor Variables

You can pass a set of rows to a PL/SQL function in a

REF CURSOR

parameter. For example, this function is declared to accept an argument of the predefined weakly typed

REF CURSOR

type

SYS_REFCURSOR

FUNCTION f(p1 IN SYS_REFCURSOR) RETURN ... ;

Results of a subquery can be passed to a function directly:

SELECT * FROM TABLE(f(CURSOR(SELECT empid FROM tab)));

In the preceding example, the

CURSOR

keyword is required to indicate that the results of a subquery should be passed as a

REF CURSOR

parameter.

A predefined weak

REF CURSOR

type

SYS_REFCURSOR

is also supported. With

SYS_REFCURSOR

, you do not need to first create a

REF CURSOR

type in a package before you can use it.

To use a strong

REF CURSOR

type, you still must create a PL/SQL package and declare a strong

REF CURSOR

type in it. Also, if you are using a strong

REF CURSOR

type as an argument to a table function, then the actual type of the

REF CURSOR

argument must match the column type, or an error is generated. Weak

REF CURSOR

arguments to table functions can only be partitioned using the

PARTITION BY ANY

clause. You cannot use range or hash partitioning for weak

REF CURSOR

arguments.

PL/SQL functions can accept multiple

REF CURSOR

input variables as shown in

Example 11–24 .

Example 11–24 Using Multiple REF CURSOR Input Variables

-- Define the ref cursor types

CREATE PACKAGE refcur_pkg IS

TYPE refcur_t1 IS REF CURSOR RETURN employees%ROWTYPE;

TYPE refcur_t2 IS REF CURSOR RETURN departments%ROWTYPE;

TYPE outrec_typ IS RECORD (

var_num NUMBER(6),

var_char1 VARCHAR2(30),

var_char2 VARCHAR2(30));

TYPE outrecset IS TABLE OF outrec_typ;

FUNCTION g_trans(p1 refcur_t1, p2 refcur_t2)

RETURN outrecset PIPELINED;

END refcur_pkg;

CREATE PACKAGE BODY refcur_pkg IS

FUNCTION g_trans(p1 refcur_t1, p2 refcur_t2)

RETURN outrecset PIPELINED IS

out_rec outrec_typ;

in_rec1 p1%ROWTYPE;

in_rec2 p2%ROWTYPE;

BEGIN

LOOP

FETCH p2 INTO in_rec2;

EXIT WHEN p2%NOTFOUND;

END LOOP;

CLOSE p2;

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LOOP

FETCH p1 INTO in_rec1;

EXIT WHEN p1%NOTFOUND;

-- first row

out_rec.var_num := in_rec1.employee_id;

out_rec.var_char1 := in_rec1.first_name;

out_rec.var_char2 := in_rec1.last_name;

PIPE ROW(out_rec);

-- second row

out_rec.var_num := in_rec2.department_id;

out_rec.var_char1 := in_rec2.department_name;

out_rec.var_char2 := TO_CHAR(in_rec2.location_id);

PIPE ROW(out_rec);

END LOOP;

CLOSE p1;

RETURN;

END;

END refcur_pkg;

-- SELECT query using the g_trans table function

SELECT * FROM TABLE(refcur_pkg.g_trans(

CURSOR(SELECT * FROM employees WHERE department_id = 60),

CURSOR(SELECT * FROM departments WHERE department_id = 60)));

You can pass table function return values to other table functions by creating a

REF

CURSOR

that iterates over the returned data:

SELECT * FROM TABLE(f(CURSOR(SELECT * FROM TABLE(g(...)))));

You can explicitly open a

REF CURSOR

for a query and pass it as a parameter to a table function:

DECLARE r SYS_REFCURSOR; rec ...;

BEGIN

SELECT * INTO rec FROM TABLE(g(r));

END;

OPEN r FOR SELECT * FROM TABLE(f(...));

-- Must return a single row result set.

In this case, the table function closes the cursor when it completes, so your program should not explicitly try to close the cursor.

A table function can compute aggregate results using the input ref cursor.

Example 11–25 computes a weighted average by iterating over a set of input rows.

Example 11–25 Using a Pipelined Table Function as an Aggregate Function

CREATE TABLE gradereport (student VARCHAR2(30), subject VARCHAR2(30),

weight NUMBER, grade NUMBER);

INSERT INTO gradereport VALUES('Mark', 'Physics', 4, 4);

INSERT INTO gradereport VALUES('Mark','Chemistry', 4, 3);

INSERT INTO gradereport VALUES('Mark','Maths', 3, 3);

INSERT INTO gradereport VALUES('Mark','Economics', 3, 4);

CREATE PACKAGE pkg_gpa IS

TYPE gpa IS TABLE OF NUMBER;

FUNCTION weighted_average(input_values SYS_REFCURSOR)

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11-37

Setting Up Transformations with Pipelined Functions

RETURN gpa PIPELINED;

END pkg_gpa;

CREATE PACKAGE BODY pkg_gpa IS

FUNCTION weighted_average(input_values SYS_REFCURSOR)

RETURN gpa PIPELINED IS

grade NUMBER;

total NUMBER := 0;

total_weight NUMBER := 0;

weight NUMBER := 0;

BEGIN

-- The function accepts a ref cursor and loops through all the input rows

LOOP

FETCH input_values INTO weight, grade;

EXIT WHEN input_values%NOTFOUND;

-- Accumulate the weighted average

total_weight := total_weight + weight;

total := total + grade*weight;

END LOOP;

PIPE ROW (total / total_weight);

RETURN; -- the function returns a single result

END;

END pkg_gpa;

-- the query result comes back as a nested table with a single row

-- COLUMN_VALUE is a keyword that returns the contents of a nested table

SELECT w.column_value "weighted result" FROM TABLE(

pkg_gpa.weighted_average(CURSOR(SELECT weight, grade FROM gradereport))) w;

Performing DML Operations Inside Pipelined Table Functions

To execute DML statements, declare a pipelined table function with the

AUTONOMOUS_TRANSACTION

pragma, which causes the function to execute in a new transaction not shared by other processes:

CREATE FUNCTION f(p SYS_REFCURSOR)

RETURN CollType PIPELINED IS

PRAGMA AUTONOMOUS_TRANSACTION;

BEGIN NULL; END;

During parallel execution, each instance of the table function creates an independent transaction.

Performing DML Operations on Pipelined Table Functions

Pipelined table functions cannot be the target table in

UPDATE

INSERT

, or

DELETE statements. For example, the following statements will raise an error:

UPDATE F(CURSOR(SELECT * FROM tab)) SET col = value;

INSERT INTO f(...) VALUES ('any', 'thing');

However, you can create a view over a table function and use

INSTEAD OF

triggers to update it. For example:

CREATE VIEW BookTable AS SELECT x.Name, x.Author

FROM TABLE(GetBooks('data.txt')) x;

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The following

INSTEAD OF

trigger is fired when the user inserts a row into the

BookTable

view:

CREATE TRIGGER BookTable_insert

INSTEAD OF INSERT ON BookTable

REFERENCING NEW AS n

FOR EACH ROW

BEGIN

...

END;

INSERT INTO BookTable VALUES (...);

INSTEAD OF

triggers can be defined for all DML operations on a view built on a table function.

Handling Exceptions in Pipelined Table Functions

Exception handling in pipelined table functions works just as it does with regular functions.

Some languages, such as C and Java, provide a mechanism for user-supplied exception handling. If an exception raised within a table function is handled, the table function executes the exception handler and continues processing. Exiting the exception handler takes control to the enclosing scope. If the exception is cleared, execution proceeds normally.

An unhandled exception in a table function causes the parent transaction to roll back.

Tuning PL/SQL Applications for Performance

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Setting Up Transformations with Pipelined Functions

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Oracle Database PL/SQL User’s Guide and Reference

Using PL/SQL With Object Types

Object-oriented programming is especially suited for building reusable components and complex applications. In PL/SQL, object-oriented programming is based on object types. They let you model real-world objects, separate interfaces and implementation details, and store object-oriented data persistently in the database.

This chapter contains these topics:

■

Declaring and Initializing Objects in PL/SQL

■

Manipulating Objects in PL/SQL

Defining SQL Types Equivalent to PL/SQL Collection Types

Using PL/SQL Collections with SQL Object Types

Using Dynamic SQL With Objects

For information about object types, see Oracle Database Application Developer's Guide -

Object-Relational Features.

Declaring and Initializing Objects in PL/SQL

An object type can represent any real-world entity. For example, an object type can represent a student, bank account, computer screen, rational number, or data structure such as a queue, stack, or list.

Currently, you cannot define object types in a PL/SQL block, subprogram, or package.

You can define them interactively in SQL*Plus using the SQL statement

CREATE

TYPE

. See Example 1–17, "Defining an Object Type" on page 1-17.

For information on the

CREATE TYPE

SQL statement, see Oracle Database SQL

Reference. For information on the

CREATE TYPE BODY

SQL statement, see Oracle

Database SQL Reference.

After an object type is defined and installed in the schema, you can use it to declare objects in any PL/SQL block, subprogram, or package. For example, you can use the object type to specify the datatype of an attribute, column, variable, bind variable, record field, table element, formal parameter, or function result. At run time, instances of the object type are created; that is, objects of that type are instantiated. Each object can hold different values.

Such objects follow the usual scope and instantiation rules. In a block or subprogram, local objects are instantiated when you enter the block or subprogram and cease to exist when you exit. In a package, objects are instantiated when you first reference the package and cease to exist when you end the database session.

Using PL/SQL With Object Types

12-1

Declaring and Initializing Objects in PL/SQL

Example 12–1 shows how to create an object type, object body type, and a table of

object types.

Example 12–1 Working With Object Types

CREATE TYPE address_typ AS OBJECT (

street VARCHAR2(30),

city VARCHAR2(20),

state CHAR(2),

postal_code VARCHAR2(6) );

CREATE TYPE employee_typ AS OBJECT (

employee_id NUMBER(6),

first_name VARCHAR2(20),

last_name VARCHAR2(25),

email VARCHAR2(25),

phone_number VARCHAR2(20),

hire_date DATE,

job_id VARCHAR2(10),

salary NUMBER(8,2),

commission_pct NUMBER(2,2),

manager_id NUMBER(6),

department_id NUMBER(4),

address address_typ,

MAP MEMBER FUNCTION get_idno RETURN NUMBER,

MEMBER PROCEDURE display_address ( SELF IN OUT NOCOPY employee_typ ) );

CREATE TYPE BODY employee_typ AS

MAP MEMBER FUNCTION get_idno RETURN NUMBER IS

BEGIN

RETURN employee_id;

END;

MEMBER PROCEDURE display_address ( SELF IN OUT NOCOPY employee_typ ) IS

BEGIN

DBMS_OUTPUT.PUT_LINE(first_name || ' ' || last_name);

DBMS_OUTPUT.PUT_LINE(address.street);

DBMS_OUTPUT.PUT_LINE(address.city || ', ' || address.state || ' ' ||

address.postal_code);

END;

CREATE TABLE employee_tab OF employee_typ;

Declaring Objects in a PL/SQL Block

You can use object types wherever built-in types such as

CHAR

NUMBER

can be used.

Example 12–2 , you declare object

emp

of type employee_typ

. Then, you call the constructor for object type employee_typ

to initialize the object.

Example 12–2 Declaring Object Types in a PL/SQL Block

DECLARE

emp employee_typ; -- emp is atomically null

BEGIN

-- call the constructor for employee_typ

emp := employee_typ(315, 'Francis', 'Logan', 'FLOGAN',

'555.777.2222', '01-MAY-04', 'SA_MAN', 11000, .15, 101, 110,

address_typ('376 Mission', 'San Francisco', 'CA', '94222'));

DBMS_OUTPUT.PUT_LINE(emp.first_name || ' ' || emp.last_name); -- display details

emp.display_address(); -- call object method to display details

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Declaring and Initializing Objects in PL/SQL

END;

You can declare objects as the formal parameters of functions and procedures. That way, you can pass objects to stored subprograms and from one subprogram to another.

In the next example, you use object type employee_typ

to specify the datatype of a formal parameter:

PROCEDURE open_acct (new_acct IN OUT employee_typ) IS ...

In the following example, you use object type employee_typ

to specify the return type of a function:

FUNCTION get_acct (acct_id IN NUMBER) RETURN employee_typ IS ...

How PL/SQL Treats Uninitialized Objects

Until you initialize an object by calling the constructor for its object type, the object is atomically null. That is, the object itself is null, not just its attributes.

A null object is never equal to another object. In fact, comparing a null object with any other object always yields

NULL

. Also, if you assign an atomically null object to another object, the other object becomes atomically null (and must be reinitialized).

Likewise, if you assign the non-value

NULL

to an object, the object becomes atomically null.

In an expression, attributes of an uninitialized object evaluate to

NULL

. When applied to an uninitialized object or its attributes, the

IS NULL

comparison operator yields

TRUE

Example 12–3 illustrates null objects and objects with null attributes.

Example 12–3 Null Objects in a PL/SQL Block

DECLARE

emp employee_typ; -- emp is atomically null

BEGIN

IF emp IS NULL THEN DBMS_OUTPUT.PUT_LINE('emp is NULL #1'); END IF;

IF emp.employee_id IS NULL THEN

DBMS_OUTPUT.PUT_LINE('emp.employee_id is NULL #1');

END IF;

emp.employee_id := 330;

IF emp IS NULL THEN DBMS_OUTPUT.PUT_LINE('emp is NULL #2'); END IF;

IF emp.employee_id IS NULL THEN

DBMS_OUTPUT.PUT_LINE('emp.employee_id is NULL #2');

END IF;

emp := employee_typ(NULL, NULL, NULL, NULL,

NULL, NULL, NULL, NULL, NULL, NULL, NULL,

address_typ(NULL, NULL, NULL, NULL));

-- emp := NULL; -- this would have made the following IF statement TRUE

IF emp IS NULL THEN DBMS_OUTPUT.PUT_LINE('emp is NULL #3'); END IF;

IF emp.employee_id IS NULL THEN

DBMS_OUTPUT.PUT_LINE('emp.employee_id is NULL #3');

END IF;

EXCEPTION

WHEN ACCESS_INTO_NULL THEN

DBMS_OUTPUT.PUT_LINE('Cannot assign value to NULL object');

END;

The output is:

Using PL/SQL With Object Types

12-3

Manipulating Objects in PL/SQL emp is NULL #1 emp.employee_id is NULL #1 emp is NULL #2 emp.employee_id is NULL #3

Calls to methods of an uninitialized object raise the predefined exception

NULL_

SELF_DISPATCH

. When passed as arguments to

parameters, attributes of an uninitialized object evaluate to

NULL

. When passed as arguments to

OUT

IN OUT parameters, they raise an exception if you try to write to them.

Manipulating Objects in PL/SQL

This section describes how to manipulate object attributes and methods in PL/SQL.

Accessing Object Attributes With Dot Notation

You refer to an attribute by name. To access or change the value of an attribute, you use dot notation. Attribute names can be chained, which lets you access the attributes of a nested object type. For example:

Example 12–4 Accessing Object Attributes

DECLARE

emp employee_typ;

BEGIN

emp := employee_typ(315, 'Francis', 'Logan', 'FLOGAN',

'555.777.2222', '01-MAY-04', 'SA_MAN', 11000, .15, 101, 110,

address_typ('376 Mission', 'San Francisco', 'CA', '94222'));

DBMS_OUTPUT.PUT_LINE(emp.first_name || ' ' || emp.last_name);

DBMS_OUTPUT.PUT_LINE(emp.address.street);

DBMS_OUTPUT.PUT_LINE(emp.address.city || ', ' ||emp. address.state || ' ' ||

emp.address.postal_code);

END;

Calling Object Constructors and Methods

Calls to a constructor are allowed wherever function calls are allowed. Like all functions, a constructor is called as part of an expression, as shown in

Example 12–4 on page 12-4 and Example 12–5 .

Example 12–5 Inserting Rows in an Object Table

DECLARE

emp employee_typ;

BEGIN

INSERT INTO employee_tab VALUES (employee_typ(310, 'Evers', 'Boston', 'EBOSTON',

'555.111.2222', '01-AUG-04', 'SA_REP', 9000, .15, 101, 110,

address_typ('123 Main', 'San Francisco', 'CA', '94111')) );

INSERT INTO employee_tab VALUES (employee_typ(320, 'Martha', 'Dunn', 'MDUNN',

'555.111.3333', '30-SEP-04', 'AC_MGR', 12500, 0, 101, 110,

address_typ('123 Broadway', 'Redwood City', 'CA', '94065')) );

END;

When you pass parameters to a constructor, the call assigns initial values to the attributes of the object being instantiated. When you call the default constructor to fill in all attribute values, you must supply a parameter for every attribute; unlike

12-4

Oracle Database PL/SQL User’s Guide and Reference

Manipulating Objects in PL/SQL constants and variables, attributes cannot have default values. You can call a constructor using named notation instead of positional notation.

Like packaged subprograms, methods are called using dot notation. In Example 12–6

, the display_address

method is called to display attributes of an object. Note the use of the

VALUE

function which returns the value of an object.

VALUE

takes as its argument a correlation variable. In this context, a correlation variable is a row variable or table alias associated with a row in an object table.

Example 12–6 Accessing Object Methods

DECLARE

emp employee_typ;

BEGIN

SELECT VALUE(e) INTO emp FROM employee_tab e WHERE e.employee_id = 310;

emp.display_address();

END;

In SQL statements, calls to a parameterless method require an empty parameter list. In procedural statements, an empty parameter list is optional unless you chain calls, in which case it is required for all but the last call. You cannot chain additional method calls to the right of a procedure call because a procedure is called as a statement, not as part of an expression. Also, if you chain two function calls, the first function must return an object that can be passed to the second function.

For static methods, calls use the notation type_name

method_name

rather than specifying an instance of the type.

When you call a method using an instance of a subtype, the actual method that is executed depends on the exact declarations in the type hierarchy. If the subtype overrides the method that it inherits from its supertype, the call uses the subtype's implementation. Or, if the subtype does not override the method, the call uses the supertype's implementation. This capability is known as dynamic method dispatch.

Note:

When implementing methods using PL/SQL, you cannot call a base or supertype object method with the super

keyword or an equivalent method in a derived object. See Oracle Database Application

Developer's Guide - Object-Relational Features for additional information on supertypes, subtypes, and object methods.

Updating and Deleting Objects

From inside a PL/SQL block you can modify and delete rows in an object table.

Example 12–7 Updating and Deleting Rows in an Object Table

DECLARE

emp employee_typ;

BEGIN

INSERT INTO employee_tab VALUES (employee_typ(370, 'Robert', 'Myers', 'RMYERS',

'555.111.2277', '07-NOV-04', 'SA_REP', 8800, .12, 101, 110,

address_typ('540 Fillmore', 'San Francisco', 'CA', '94011')) );

UPDATE employee_tab e SET e.address.street = '1040 California'

WHERE e.employee_id = 370;

DELETE FROM employee_tab e WHERE e.employee_id = 310;

END;

Using PL/SQL With Object Types

12-5

Defining SQL Types Equivalent to PL/SQL Collection Types

Manipulating Objects Through Ref Modifiers

You can retrieve refs using the function

REF

, which takes as its argument a correlation variable.

Example 12–8 Updating Rows in an Object Table With a REF Modifier

DECLARE

emp employee_typ;

emp_ref REF employee_typ;

BEGIN

SELECT REF(e) INTO emp_ref FROM employee_tab e WHERE e.employee_id = 370;

UPDATE employee_tab e

SET e.address = address_typ('8701 College', 'Oakland', 'CA', '94321')

WHERE REF(e) = emp_ref;

END;

You can declare refs as variables, parameters, fields, or attributes. You can use refs as input or output variables in SQL data manipulation statements.

You cannot navigate through refs in PLSQL. For example, the assignment in

Example 12–9 using a ref is not allowed. Instead, use the function

DEREF

or make calls to the package

UTL_REF

to access the object. For information on the

REF

function, see

Oracle Database SQL Reference.

Example 12–9 Using DEREF in a SELECT INTO Statement

DECLARE

emp employee_typ;

emp_ref REF employee_typ;

emp_name VARCHAR2(50);

BEGIN

SELECT REF(e) INTO emp_ref FROM employee_tab e WHERE e.employee_id = 370;

-- the following assignment raises an error, not allowed in PL/SQL

-- emp_name := emp_ref.first_name || ' ' || emp_ref.last_name;

-- emp := DEREF(emp_ref); not allowed, cannot use DEREF in procedural statements

SELECT DEREF(emp_ref) INTO emp FROM DUAL; -- use dummy table DUAL

emp_name := emp.first_name || ' ' || emp.last_name;

DBMS_OUTPUT.PUT_LINE(emp_name);

END;

For information on the

DEREF

function, see Oracle Database SQL Reference.

Defining SQL Types Equivalent to PL/SQL Collection Types

To store nested tables and varrays inside database tables, you must also declare SQL types using the

CREATE TYPE

statement. The SQL types can be used as columns or as attributes of SQL object types. For information on the

CREATE TYPE

SQL statement, see Oracle Database SQL Reference. For information on the

CREATE TYPE BODY

SQL statement, see Oracle Database SQL Reference. For more information on object types, see

Oracle Database Application Developer's Guide - Object-Relational Features.

You can declare equivalent types within PL/SQL, or use the SQL type name in a

PL/SQL variable declaration.

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Oracle Database PL/SQL User’s Guide and Reference

Defining SQL Types Equivalent to PL/SQL Collection Types

Example 12–10

shows how you might declare a nested table in SQL, and use it as an attribute of an object type.

Example 12–10 Declaring a Nested Table in SQL

CREATE TYPE CourseList AS TABLE OF VARCHAR2(10) -- define type

CREATE TYPE student AS OBJECT ( -- create object

id_num INTEGER(4),

name VARCHAR2(25),

address VARCHAR2(35),

status CHAR(2),

courses CourseList); -- declare nested table as attribute

CREATE TABLE sophomores of student

NESTED TABLE courses STORE AS courses_nt;

The identifier courses

represents an entire nested table. Each element of courses stores the name of a college course such as

'Math 1020'

Example 12–11 creates a database column that stores varrays. Each varray element

contains a

VARCHAR2

Example 12–11 Creating a Table with a Varray Column

-- Each project has a 16-character code name.

-- We will store up to 50 projects at a time in a database column.

CREATE TYPE ProjectList AS VARRAY(50) OF VARCHAR2(16);

CREATE TABLE dept_projects ( -- create database table

dept_id NUMBER(2),

name VARCHAR2(15),

budget NUMBER(11,2),

-- Each department can have up to 50 projects.

projects ProjectList);

Example 12–12 , you insert a row into database table

dept_projects

. The varray constructor

ProjectList()

provides a value for column projects

Example 12–12 Varray Constructor Within a SQL Statement

BEGIN

INSERT INTO dept_projects

VALUES(60, 'Security', 750400,

ProjectList('New Badges', 'Track Computers', 'Check Exits'));

END;

Example 12–13 , you insert several scalar values and a

CourseList

nested table into the sophomores

table.

Example 12–13 Nested Table Constructor Within a SQL Statement

CREATE TABLE sophomores of student

NESTED TABLE courses STORE AS courses_nt;

BEGIN

INSERT INTO sophomores

VALUES (5035, 'Janet Alvarez', '122 Broad St', 'FT',

CourseList('Econ 2010', 'Acct 3401', 'Mgmt 3100'));

END;

Using PL/SQL With Object Types

12-7

Defining SQL Types Equivalent to PL/SQL Collection Types

Manipulating Individual Collection Elements with SQL

By default, SQL operations store and retrieve whole collections rather than individual elements. To manipulate the individual elements of a collection with SQL, use the

TABLE

operator. The

TABLE

operator uses a subquery to extract the varray or nested table, so that the

INSERT

UPDATE

, or

DELETE

statement applies to the nested table rather than the top-level table.

To perform DML operations on a PL/SQL nested table, use the operators

TABLE

and

CAST

. This way, you can do set operations on nested tables using SQL notation, without actually storing the nested tables in the database.

The operands of

CAST

are PL/SQL collection variable and a SQL collection type

(created by the

CREATE TYPE

statement).

CAST

converts the PL/SQL collection to the

SQL type.

Example 12–14 Performing Operations on PL/SQL Nested Tables With CAST

CREATE TYPE Course AS OBJECT

(course_no NUMBER,

title VARCHAR2(64),

credits NUMBER);

CREATE TYPE CourseList AS TABLE OF course;

-- create department table

CREATE TABLE department (

name VARCHAR2(20),

director VARCHAR2(20),

office VARCHAR2(20),

courses CourseList)

NESTED TABLE courses STORE AS courses_tab;

INSERT INTO department VALUES ('English', 'June Johnson', '491C',

CourseList(Course(1002, 'Expository Writing', 4),

Course(2020, 'Film and Literature', 4),

Course(4210, '20th-Century Poetry', 4),

Course(4725, 'Advanced Workshop in Poetry', 4)));

DECLARE

revised CourseList :=

CourseList(Course(1002, 'Expository Writing', 3),

Course(2020, 'Film and Literature', 4),

Course(4210, '20th-Century Poetry', 4),

Course(4725, 'Advanced Workshop in Poetry', 5));

num_changed INTEGER;

BEGIN

SELECT COUNT(*) INTO num_changed

FROM TABLE(CAST(revised AS CourseList)) new,

TABLE(SELECT courses FROM department

WHERE name = 'English') old

WHERE new.course_no = old.course_no AND

(new.title != old.title OR new.credits != old.credits);

DBMS_OUTPUT.PUT_LINE(num_changed);

END;

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Oracle Database PL/SQL User’s Guide and Reference

Using PL/SQL Collections with SQL Object Types

Collections let you manipulate complex datatypes within PL/SQL. Your program can compute subscripts to process specific elements in memory, and use SQL to store the results in database tables.

In SQL*Plus, you can create SQL object types whose definitions correspond to PL/SQL nested tables and varrays, as shown in

Example 12–15 . Each item in column

dept_ names

is a nested table that will store the department names for a specific region. The

NESTED TABLE

clause is required whenever a database table has a nested table column. The clause identifies the nested table and names a system-generated store table, in which Oracle stores the nested table data.

Within PL/SQL, you can manipulate the nested table by looping through its elements, using methods such as

TRIM

EXTEND

, and updating some or all of the elements.

Afterwards, you can store the updated table in the database again. You can insert table rows containing nested tables, update rows to replace its nested table, and select nested tables into PL/SQL variables. You cannot update or delete individual nested table elements directly with SQL; you have to select the nested table from the table, change it in PL/SQL, then update the table to include the new nested table.

Example 12–15 Using INSERT, UPDATE, DELETE, and SELECT Statements With Nested

Tables

CREATE TYPE dnames_tab AS TABLE OF VARCHAR2(30);

CREATE TABLE depts (region VARCHAR2(25), dept_names dnames_tab)

NESTED TABLE dept_names STORE AS dnames_nt;

BEGIN

INSERT INTO depts VALUES('Europe', dnames_tab('Shipping','Sales','Finance'));

INSERT INTO depts VALUES('Americas', dnames_tab('Sales','Finance','Shipping'));

INSERT INTO depts VALUES('Asia', dnames_tab('Finance','Payroll'));

COMMIT;

END;

DECLARE

-- Type declaration is not needed, because PL/SQL can access the SQL object type

-- TYPE dnames_tab IS TABLE OF VARCHAR2(30); not needed

-- Declare a variable that can hold a set of department names

v_dnames dnames_tab;

-- Declare a record that can hold a row from the table

-- One of the record fields is a set of department names

v_depts depts%ROWTYPE;

new_dnames dnames_tab;

BEGIN

-- Look up a region and query just the associated department names

SELECT dept_names INTO v_dnames FROM depts WHERE region = 'Europe';

FOR i IN v_dnames.FIRST .. v_dnames.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Department names: ' || v_dnames(i));

END LOOP;

-- Look up a region and query the entire row

SELECT * INTO v_depts FROM depts WHERE region = 'Asia';

-- Now dept_names is a field in a record, so we access it with dot notation

FOR i IN v_depts.dept_names.FIRST .. v_depts.dept_names.LAST LOOP

-- Because we have all the table columns in the record, we can refer to region

DBMS_OUTPUT.PUT_LINE(v_depts.region || ' dept_names = ' ||

v_depts.dept_names(i));

END LOOP;

-- We can replace a set of department names with a new collection

Using PL/SQL With Object Types

12-9

Using PL/SQL Collections with SQL Object Types

-- in an UPDATE statement

new_dnames := dnames_tab('Sales','Payroll','Shipping');

UPDATE depts SET dept_names = new_dnames WHERE region = 'Europe';

-- Or we can modify the original collection and use it in the UPDATE.

-- We'll add a new final element and fill in a value

v_depts.dept_names.EXTEND(1);

v_depts.dept_names(v_depts.dept_names.COUNT) := 'Finance';

UPDATE depts SET dept_names = v_depts.dept_names

WHERE region = v_depts.region;

-- We can even treat the nested table column like a real table and

-- insert, update, or delete elements. The TABLE operator makes the statement

-- apply to the nested table produced by the subquery.

INSERT INTO TABLE(SELECT dept_names FROM depts WHERE region = 'Asia')

VALUES('Sales');

DELETE FROM TABLE(SELECT dept_names FROM depts WHERE region = 'Asia')

WHERE column_value = 'Payroll';

UPDATE TABLE(SELECT dept_names FROM depts WHERE region = 'Americas')

SET column_value = 'Payroll' WHERE column_value = 'Finance';

COMMIT;

END;

Example 12–16

shows how you can manipulate SQL varray object types with PL/SQL statements. In this example, varrays are transferred between PL/SQL variables and

SQL tables. You can insert table rows containing varrays, update a row to replace its varray, and select varrays into PL/SQL variables. You cannot update or delete individual varray elements directly with SQL; you have to select the varray from the table, change it in PL/SQL, then update the table to include the new varray.

Example 12–16 Using INSERT, UPDATE, DELETE, and SELECT Statements With Varrays

-- By using a varray, we put an upper limit on the number of elements

-- and ensure they always come back in the same order

CREATE TYPE dnames_var IS VARRAY(7) OF VARCHAR2(30);

CREATE TABLE depts (region VARCHAR2(25), dept_names dnames_var);

BEGIN

INSERT INTO depts VALUES('Europe', dnames_var('Shipping','Sales','Finance'));

INSERT INTO depts VALUES('Americas', dnames_var('Sales','Finance','Shipping'));

INSERT INTO depts

VALUES('Asia', dnames_var('Finance','Payroll','Shipping','Sales'));

COMMIT;

END;

DECLARE

new_dnames dnames_var := dnames_var('Benefits', 'Advertising', 'Contracting',

'Executive', 'Marketing');

some_dnames dnames_var;

BEGIN

UPDATE depts SET dept_names = new_dnames WHERE region = 'Europe';

COMMIT;

SELECT dept_names INTO some_dnames FROM depts WHERE region = 'Europe';

FOR i IN some_dnames.FIRST .. some_dnames.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('dept_names = ' || some_dnames(i));

END LOOP;

END;

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Oracle Database PL/SQL User’s Guide and Reference

Using Dynamic SQL With Objects

Example 12–17 , PL/SQL

BULK COLLECT

is used with a multilevel collection that includes an object type.

Example 12–17 Using BULK COLLECT with Nested Tables

CREATE TYPE dnames_var IS VARRAY(7) OF VARCHAR2(30);

CREATE TABLE depts (region VARCHAR2(25), dept_names dnames_var);

BEGIN

INSERT INTO depts VALUES('Europe', dnames_var('Shipping','Sales','Finance'));

INSERT INTO depts VALUES('Americas', dnames_var('Sales','Finance','Shipping'));

INSERT INTO depts

VALUES('Asia', dnames_var('Finance','Payroll','Shipping','Sales'));

COMMIT;

END;

DECLARE

TYPE dnames_tab IS TABLE OF dnames_var;

v_depts dnames_tab;

BEGIN

SELECT dept_names BULK COLLECT INTO v_depts FROM depts;

DBMS_OUTPUT.PUT_LINE(v_depts.COUNT); -- prints 3

END;

Using Dynamic SQL With Objects

Example 12–18

illustrates the use of objects and collections with dynamic SQL. First, define object type person_typ

and

VARRAY

type hobbies_var

, then write a package that uses these types.

Example 12–18 TEAMS Package Using Dynamic SQL for Object Types and Collections

CREATE TYPE person_typ AS OBJECT (name VARCHAR2(25), age NUMBER);

CREATE TYPE hobbies_var AS VARRAY(10) OF VARCHAR2(25);

CREATE OR REPLACE PACKAGE teams

AUTHID CURRENT_USER AS

PROCEDURE create_table (tab_name VARCHAR2);

PROCEDURE insert_row (tab_name VARCHAR2, p person_typ, h hobbies_var);

PROCEDURE print_table (tab_name VARCHAR2);

END;

CREATE OR REPLACE PACKAGE BODY teams AS

PROCEDURE create_table (tab_name VARCHAR2) IS

BEGIN

EXECUTE IMMEDIATE 'CREATE TABLE ' || tab_name ||

' (pers person_typ, hobbs hobbies_var)';

END;

PROCEDURE insert_row (

tab_name VARCHAR2,

p person_typ,

h hobbies_var) IS

BEGIN

EXECUTE IMMEDIATE 'INSERT INTO ' || tab_name ||

' VALUES (:1, :2)' USING p, h;

END;

PROCEDURE print_table (tab_name VARCHAR2) IS

Using PL/SQL With Object Types

12-11

Using Dynamic SQL With Objects

TYPE refcurtyp IS REF CURSOR;

v_cur refcurtyp;

p person_typ;

h hobbies_var;

BEGIN

OPEN v_cur FOR 'SELECT pers, hobbs FROM ' || tab_name;

LOOP

FETCH v_cur INTO p, h;

EXIT WHEN v_cur%NOTFOUND;

-- print attributes of 'p' and elements of 'h'

DBMS_OUTPUT.PUT_LINE('Name: ' || p.name || ' - Age: ' || p.age);

FOR i IN h.FIRST..h.LAST

LOOP

DBMS_OUTPUT.PUT_LINE('Hobby(' || i || '): ' || h(i));

END LOOP;

CLOSE v_cur;

END;

From an anonymous block, you might call the procedures in package

TEAMS

Example 12–19 Calling Procedures from the TEAMS Package

DECLARE

team_name VARCHAR2(15);

BEGIN

team_name := 'Notables';

TEAMS.create_table(team_name);

TEAMS.insert_row(team_name, person_typ('John', 31),

hobbies_var('skiing', 'coin collecting', 'tennis'));

TEAMS.insert_row(team_name, person_typ('Mary', 28),

hobbies_var('golf', 'quilting', 'rock climbing', 'fencing'));

TEAMS.print_table(team_name);

END;

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Oracle Database PL/SQL User’s Guide and Reference

PL/SQL Language Elements

This chapter is a quick reference guide to PL/SQL syntax and semantics. It shows you how commands, parameters, and other language elements are combined to form

PL/SQL statements. It also provides usage notes and links to examples.

To understand the syntax of a PL/SQL statement, trace through its syntax diagram, reading from left to right and top to bottom. The diagrams represent Backus-Naur

Form (BNF) productions. Within the diagrams, keywords are enclosed in boxes, delimiters in circles, and identifiers in ovals. Each diagram defines a syntactic element.

Every path through the diagram describes a possible form of that element. Follow in the direction of the arrows. If a line loops back on itself, you can repeat the element enclosed by the loop.

This chapter contains these topics:

■

Assignment Statement

■

AUTONOMOUS_TRANSACTION Pragma

Block Declaration

■

CASE Statement

CLOSE Statement

Collection Definition

Collection Methods

Comments

COMMIT Statement

Constant and Variable Declaration

■

EXCEPTION_INIT Pragma

Exception Definition

EXECUTE IMMEDIATE Statement

EXIT Statement

Expression Definition

FETCH Statement

PL/SQL Language Elements

13-1

■

Object Type Declaration

OPEN Statement

OPEN-FOR Statement

Package Declaration

Procedure Declaration

RAISE Statement

Record Definition

RESTRICT_REFERENCES Pragma

RETURN Statement

RETURNING INTO Clause

ROLLBACK Statement

%ROWTYPE Attribute

SAVEPOINT Statement

SELECT INTO Statement

SERIALLY_REUSABLE Pragma

SET TRANSACTION Statement

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Oracle Database PL/SQL User’s Guide and Reference

Assignment Statement

An assignment statement sets the current value of a variable, field, parameter, or element. The statement consists of an assignment target followed by the assignment operator and an expression. When the statement is executed, the expression is evaluated and the resulting value is stored in the target. For more information, see

"Assigning Values to Variables" on page 2-18.

Syntax

assignment statement ::=

( index collection_name cursor_variable_name

: host_cursor_variable_name

)

: indicator_name

: host_variable_name

attribute_name object_name parameter_name

field_name record_name variable_name

:= expression ;

Keyword and Parameter Description

attribute_name

An attribute of an object type. The name must be unique within the object type (but can be reused in other object types). You cannot initialize an attribute in its declaration using the assignment operator or

DEFAULT

clause. Also, you cannot impose the

NOT

NULL

constraint on an attribute.

collection_name

A nested table, index-by table, or varray previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable previously declared within the current scope. Only the value of another cursor variable can be assigned to a cursor variable.

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. For the syntax of expression

, see

"Expression Definition" on page 13-45. When the assignment statement is executed, the

expression is evaluated and the resulting value is stored in the assignment target. The value and target must have compatible datatypes.

PL/SQL Language Elements

13-3

Assignment Statement

field_name

A field in a user-defined or

%ROWTYPE

record.

host_cursor_variable_name

A cursor variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. The datatype of the host cursor variable is compatible with the return type of any PL/SQL cursor variable. Host variables must be prefixed with a colon.

host_variable_name

A variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. Host variables must be prefixed with a colon.

index

A numeric expression that must return a value of type

PLS_INTEGER

BINARY_INTEGER

, or a value implicitly convertible to that datatype.

indicator_name

An indicator variable declared in a PL/SQL host environment and passed to PL/SQL.

Indicator variables must be prefixed with a colon. An indicator variable indicates the value or condition of its associated host variable. For example, in the Oracle

Precompiler environment, indicator variables let you detect nulls or truncated values in output host variables.

object_name

An instance of an object type previously declared within the current scope.

parameter_name

A formal

OUT

IN OUT

parameter of the subprogram in which the assignment statement appears.

record_name

A user-defined or

%ROWTYPE

record previously declared within the current scope.

variable_name

A PL/SQL variable previously declared within the current scope.

Usage Notes

By default, unless a variable is initialized in its declaration, it is initialized to

NULL every time a block or subprogram is entered. Always assign a value to a variable before using that variable in an expression.

You cannot assign nulls to a variable defined as

NOT NULL

. If you try, PL/SQL raises the predefined exception

VALUE_ERROR

. Only the values

TRUE

FALSE

, and

NULL

can be assigned to a Boolean variable. You can assign the result of a comparison or other test to a Boolean variable.

You can assign the value of an expression to a specific field in a record. You can assign values to all fields in a record at once. PL/SQL allows aggregate assignment between

entire records if their declarations refer to the same cursor or table. Example 1–2,

"Assigning Values to Variables With the Assignment Operator" on page 1-6 shows how

to copy values from all the fields of one record to another:

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Oracle Database PL/SQL User’s Guide and Reference

Assignment Statement

You can assign the value of an expression to a specific element in a collection, by subscripting the collection name.

Examples

Example 13–1 illustrates various ways to declare and then assign values to variables.

Example 13–1 Declaring and Assigning Values to Variables

DECLARE

wages NUMBER;

hours_worked NUMBER := 40;

hourly_salary CONSTANT NUMBER := 17.50; -- constant value does not change

country VARCHAR2(64) := 'UNKNOWN';

unknown BOOLEAN;

TYPE comm_tab IS TABLE OF NUMBER INDEX BY PLS_INTEGER;

commissions comm_tab;

TYPE jobs_var IS VARRAY(10) OF employees.job_id%TYPE;

jobids jobs_var;

CURSOR c1 IS SELECT department_id FROM departments; -- cursor declaration

deptid departments.department_id%TYPE;

emp_rec employees%ROWTYPE; -- do not need TYPE declaration in this case

BEGIN

/* the following are examples of assignment statements */

wages := hours_worked * hourly_salary; -- compute wages

country := UPPER('italy');

unknown := (country = 'UNKNOWN');

commissions(5) := 20000 * 0.15; commissions(8) := 20000 * 0.18;

jobids := jobs_var('ST_CLERK'); jobids.EXTEND(1); jobids(2) := 'SH_CLERK';

OPEN c1; FETCH c1 INTO deptid; CLOSE c1;

emp_rec.department_id := deptid; emp_rec.job_id := jobids(2);

END;

For examples, see the following:

Example 1–2, "Assigning Values to Variables With the Assignment Operator" on page 1-6

Example 1–3, "Assigning Values to Variables by SELECTing INTO" on page 1-6

Example 1–4, "Assigning Values to Variables as Parameters of a Subprogram" on page 1-7

Example 2–10, "Assigning Values to a Record With a %ROWTYPE Declaration" on page 2-12

"Constant and Variable Declaration" on page 13-25

"Doing Independent Units of Work with Autonomous Transactions" on page 6-37.

PL/SQL Language Elements

13-5

AUTONOMOUS_TRANSACTION Pragma

The

AUTONOMOUS_TRANSACTION

pragma changes the way a subprogram works within a transaction. A subprogram marked with this pragma can do SQL operations and commit or roll back those operations, without committing or rolling back the data in the main transaction. For more information, see

Syntax

pragma autonomous_transaction ::=

PRAGMA AUTONOMOUS_TRANSACTION ;

Keyword and Parameter Description

PRAGMA

Signifies that the statement is a pragma (compiler directive). Pragmas are processed at compile time, not at run time. They pass information to the compiler.

Usage Notes

You can apply this pragma to:

■

Top-level (not nested) anonymous PL/SQL blocks

■

Local, standalone, and packaged functions and procedures

Methods of a SQL object type

■

Database triggers

You cannot apply this pragma to an entire package or an entire an object type. Instead, you can apply the pragma to each packaged subprogram or object method.

You can code the pragma anywhere in the declarative section. For readability, code the pragma at the top of the section.

Unlike regular triggers, autonomous triggers can contain transaction control statements such as

COMMIT

and

ROLLBACK

, and can issue DDL statements (such as

CREATE

and

DROP

) through the

EXECUTE IMMEDIATE

statement.

Changes made by an autonomous transaction become visible to other transactions when the autonomous transaction commits. The changes also become visible to the main transaction when it resumes, but only if its isolation level is set to

READ

COMMITTED

(the default). If you set the isolation level of the main transaction to

SERIALIZABLE

, changes made by its autonomous transactions are not visible to the main transaction when it resumes.

In the main transaction, rolling back to a savepoint located before the call to the autonomous subprogram does not roll back the autonomous transaction. Remember, autonomous transactions are fully independent of the main transaction.

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Oracle Database PL/SQL User’s Guide and Reference

AUTONOMOUS_TRANSACTION Pragma

If an autonomous transaction attempts to access a resource held by the main transaction (which cannot resume until the autonomous routine exits), a deadlock can occur. Oracle raises an exception in the autonomous transaction, which is rolled back if the exception goes unhandled.

If you try to exit an active autonomous transaction without committing or rolling back,

Oracle raises an exception. If the exception goes unhandled, or if the transaction ends because of some other unhandled exception, the transaction is rolled back.

Examples

For examples, see the following:

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Example 6–44, "Declaring an Autonomous Standalone Procedure" on page 6-38

Example 6–45, "Declaring an Autonomous PL/SQL Block" on page 6-38

Example 6–46, "Declaring an Autonomous Trigger" on page 6-38

Related Topics

"RESTRICT_REFERENCES Pragma" on page 13-98

"SERIALLY_REUSABLE Pragma" on page 13-111

PL/SQL Language Elements

13-7

Block Declaration

The basic program unit in PL/SQL is the block. A PL/SQL block is defined by the keywords

DECLARE

BEGIN

EXCEPTION

, and

END

. These keywords partition the block into a declarative part, an executable part, and an exception-handling part. Only the executable part is required. You can nest a block within another block wherever

you can place an executable statement. For more information, see "Understanding

PL/SQL Block Structure" on page 1-4 and

"Scope and Visibility of PL/SQL Identifiers" on page 2-15.

Syntax

plsql block ::=

<< label_name >> DECLARE type_definition item_definition function_declaration procedure_declaration

BEGIN statement

EXCEPTION exception_handler label_name

END

type definition ::=

record_type_definition ref_cursor_type_definition table_type_definition subtype_definition varray_type_definition

subtype definition ::=

SUBTYPE subtype_name IS base_type

( constraint )

;

NOT NULL

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Oracle Database PL/SQL User’s Guide and Reference

item definition ::=

collection_declaration constant_declaration cursor_declaration cursor_variable_declaration exception_declaration object_declaration object_ref_declaration record_declaration variable_declaration

sql_statement ::=

commit_statement delete_statement insert_statement lock_table_statement rollback_statement savepoint_statement select_statement set_transaction_statement update_statement

Block Declaration

PL/SQL Language Elements

13-9

Block Declaration

statement ::=

<< label_name >> assignment_statement close_statement execute_immediate_statement exit_statement fetch_statement forall_statement goto_statement if_statement loop_statement null_statement open_statement open_for_statement plsql_block raise_statement return_statement sql_statement

Keyword and Parameter Description

base_type

Any scalar or user-defined PL/SQL datatype specifier such as

CHAR

DATE

, or

RECORD

BEGIN

Signals the start of the executable part of a PL/SQL block, which contains executable statements. A PL/SQL block must contain at least one executable statement (even just the

NULL

statement). See

"Understanding PL/SQL Block Structure" on page 1-4.

collection_declaration

Declares a collection (index-by table, nested table, or varray). For the syntax of collection_declaration

, see

"Collection Definition" on page 13-17.

constant_declaration

Declares a constant. For the syntax of constant_declaration

, see

"Constant and

Declaration" on page 13-33.

constraint

Applies only to datatypes that can be constrained such as

CHAR

and

NUMBER

. For character datatypes, this specifies a maximum size in bytes. For numeric datatypes, this specifies a maximum precision and scale.

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Oracle Database PL/SQL User’s Guide and Reference

Block Declaration

cursor_declaration

Declares an explicit cursor. For the syntax of cursor_declaration

, see

"Cursor

cursor_variable_declaration

Declares a cursor variable. For the syntax of cursor_variable_declaration

, see

"Cursor Variables" on page 13-30.

DECLARE

Signals the start of the declarative part of a PL/SQL block, which contains local declarations. Items declared locally exist only within the current block and all its sub-blocks and are not visible to enclosing blocks. The declarative part of a PL/SQL block is optional. It is terminated implicitly by the keyword

BEGIN

, which introduces the executable part of the block. For more information, see

"Declarations" on page 2-8.

PL/SQL does not allow forward references. You must declare an item before referencing it in any other statements. Also, you must declare subprograms at the end of a declarative section after all other program items.

END

Signals the end of a PL/SQL block. It must be the last keyword in a block. Remember,

END

does not signal the end of a transaction. Just as a block can span multiple

transactions, a transaction can span multiple blocks. See "Understanding PL/SQL

Block Structure" on page 1-4.

EXCEPTION

Signals the start of the exception-handling part of a PL/SQL block. When an exception is raised, normal execution of the block stops and control transfers to the appropriate exception handler. After the exception handler completes, execution proceeds with the

statement following the block. See "Understanding PL/SQL Block Structure" on page 1-4.

If there is no exception handler for the raised exception in the current block, control passes to the enclosing block. This process repeats until an exception handler is found or there are no more enclosing blocks. If PL/SQL can find no exception handler for the exception, execution stops and an unhandled exception

error is returned to the host environment. For more information on exceptions, see

Chapter 10 .

exception_declaration

Declares an exception. For the syntax of exception_declaration

, see

exception_handler

Associates an exception with a sequence of statements, which is executed when that exception is raised. For the syntax of exception_handler

, see

Declaration" on page 13-59.

function_declaration

Declares a function. For the syntax of function_declaration

, see

"Function

PL/SQL Language Elements

13-11

Block Declaration

Examples

label_name

An undeclared identifier that optionally labels a PL/SQL block or statement. If used, label_name

must be enclosed by double angle brackets and must appear at the beginning of the block or statement which it labels. Optionally, when used to label a block, the label_name

can also appear at the end of the block without the angle brackets. Multiple labels are allowed for a block or statement, but they must be unique for each block or statement.

A global identifier declared in an enclosing block can be redeclared in a sub-block, in which case the local declaration prevails and the sub-block cannot reference the global

identifier unless you use a block label to qualify the reference. See Example 2–19,

"PL/SQL Block Using Multiple and Duplicate Labels" on page 2-17.

object_declaration

Declares an instance of an object type. For the syntax of object_declaration

, see

"Object Type Declaration" on page 13-78.

procedure_declaration

Declares a procedure. For the syntax of procedure_declaration

, see

"Procedure

Declaration" on page 13-90.

record_declaration

Declares a user-defined record. For the syntax of record_declaration

, see "Record

Definition" on page 13-95.

statement

An executable (not declarative) statement that. A sequence of statements can include procedural statements such as

RAISE

, SQL statements such as

UPDATE

, and PL/SQL blocks. PL/SQL statements are free format. That is, they can continue from line to line if you do not split keywords, delimiters, or literals across lines. A semicolon (

;

) serves as the statement terminator.

subtype_name

A user-defined subtype that was defined using any scalar or user-defined PL/SQL datatype specifier such as

CHAR

DATE

, or

RECORD

variable_declaration

Declares a variable. For the syntax of variable_declaration

, see "Constant and

Example 1–4, "Assigning Values to Variables as Parameters of a Subprogram" on page 1-7

PL/SQL supports a subset of SQL statements that includes data manipulation, cursor control, and transaction control statements but excludes data definition and data control statements such as

ALTER

CREATE

GRANT

, and

REVOKE

For examples, see the following:

Example 2–19, "PL/SQL Block Using Multiple and Duplicate Labels" on page 2-17

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

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Oracle Database PL/SQL User’s Guide and Reference

Example 13–2 shows the use of a simple CASE statement.

Block Declaration

PL/SQL Language Elements

13-13

CASE Statement

The

CASE

statement chooses from a sequence of conditions, and executes a corresponding statement. The

CASE

statement evaluates a single expression and compares it against several potential values, or evaluates multiple Boolean expressions and chooses the first one that is

TRUE

Syntax

searched case statement ::=

label_name

CASE WHEN boolean_expression THEN statement ;

ELSE statement ; label_name

END CASE

simple case statement ::=

label_name

;

CASE case_operand

WHEN when_operand THEN statement ;

ELSE statement ; label_name

END CASE ;

Keyword and Parameter Description

The value of the

CASE

operand and

WHEN

operands in a simple

CASE

statement can be any PL/SQL type other than

BLOB

BFILE

, an object type, a PL/SQL record, an index-by table, a varray, or a nested table.

If the

ELSE

clause is omitted, the system substitutes a default action. For a

CASE statement, the default when none of the conditions matches is to raise a

CASE_NOT_FOUND

exception. For a

CASE

expression, the default is to return

NULL

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Oracle Database PL/SQL User’s Guide and Reference

CASE Statement

Usage Notes

The

WHEN

clauses are executed in order. Each

WHEN

clause is executed only once. After a matching

WHEN

clause is found, subsequent

WHEN

clauses are not executed. You can use multiple statements after a

WHEN

clause, and that the expression in the

WHEN

clause can be a literal, variable, function call, or any other kind of expression. The

WHEN clauses can use different conditions rather than all testing the same variable or using the same operator.

The statements in a

WHEN

clause can modify the database and call non-deterministic functions. There is no fall-through mechanism as in the C switch

statement. Once a

WHEN

clause is matched and its statements are executed, the

CASE

statement ends.

The

CASE

statement is appropriate when there is some different action to be taken for each alternative. If you just need to choose among several values to assign to a variable, you can code an assignment statement using a

CASE

expression instead.

You can include

CASE

expressions inside SQL queries, for example instead of a call to the

DECODE

function or some other function that translates from one value to another.

Examples

Example 13–2 Using a CASE Statement

DECLARE

jobid employees.job_id%TYPE;

empid employees.employee_id%TYPE := 115;

sal_raise NUMBER(3,2);

BEGIN

SELECT job_id INTO jobid from employees WHERE employee_id = empid;

CASE

WHEN jobid = 'PU_CLERK' THEN sal_raise := .09;

WHEN jobid = 'SH_CLERK' THEN sal_raise := .08;

WHEN jobid = 'ST_CLERK' THEN sal_raise := .07;

ELSE sal_raise := 0;

END CASE;

END;

For examples, see the following:

Example 1–7, "Using the IF-THEN_ELSE and CASE Statement for Conditional

Control" on page 1-10

Example 4–6, "Using the CASE-WHEN Statement" on page 4-4

Example 4–7, "Using the Searched CASE Statement" on page 4-5

"CASE Expressions" on page 2-26

"Using CASE Statements" on page 4-4

NULLIF

and

COALESCE

functions in Oracle Database SQL Reference

PL/SQL Language Elements

13-15

CLOSE Statement

The

statement indicates that you are finished fetching from a cursor or cursor variable, and that the resources held by the cursor can be reused.

Syntax

close ::=

CLOSE cursor_name cursor_variable_name

: host_cursor_variable_name

;

Keyword and Parameter Description

cursor_name, cursor_variable_name, host_cursor_variable_name

When you close the cursor, you can specify an explicit cursor or a PL/SQL cursor variable, previously declared within the current scope and currently open.

You can also specify a cursor variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. The datatype of the host cursor variable is compatible with the return type of any PL/SQL cursor variable. Host variables must be prefixed with a colon.

Usage Notes

Once a cursor or cursor variable is closed, you can reopen it using the

OPEN

OPEN-FOR

statement, respectively. You must close a cursor before opening it again, otherwise PL/SQL raises the predefined exception

CURSOR_ALREADY_OPEN

. You do not need to close a cursor variable before opening it again.

If you try to close an already-closed or never-opened cursor or cursor variable,

PL/SQL raises the predefined exception

INVALID_CURSOR

Examples

For examples, see the following:

Example 4–17, "Using EXIT in a LOOP" on page 4-12

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"Closing a Cursor" on page 6-12

"Querying Data with PL/SQL" on page 6-14

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Oracle Database PL/SQL User’s Guide and Reference

Collection Definition

A collection is an ordered group of elements, all of the same type. For example, the grades for a class of students. Each element has a unique subscript that determines its position in the collection. PL/SQL offers three kinds of collections: associative arrays, nested tables, and varrays (short for variable-size arrays). Nested tables extend the functionality of associative arrays (formerly called PL/SQL tables or index-by tables).

Collections work like the arrays found in most third-generation programming languages. Collections can have only one dimension. Most collections are indexed by integers, although associative arrays can also be indexed by strings. To model multi-dimensional arrays, you can declare collections whose items are other collections.

Nested tables and varrays can store instances of an object type and, conversely, can be attributes of an object type. Collections can also be passed as parameters. You can use them to move columns of data into and out of database tables or between client-side applications and stored subprograms.

For more information, see

"Defining Collection Types and Declaring Collection

Variables" on page 5-6.

Note:

Schema level collection types created with the

CREATE TYPE statement have a different syntax than PL/SQL collection types. For information on the

CREATE TYPE

SQL statement, see Oracle Database

SQL Reference. For information on the

CREATE TYPE BODY

SQL statement, see Oracle Database SQL Reference.

Syntax

table type definition ::=

NOT NULL

TYPE type_name IS TABLE OF element_type

INDEX BY

PLS_INTEGER

BINARY_INTEGER

VARCHAR2 ( v_size )

;

varray type definition ::=

TYPE type_name IS

VARRAY

VARRYING ARRAY

( size_limit )

NOT NULL

OF element_type ;

PL/SQL Language Elements

13-17

Collection Definition

collection type definition ::=

collection_name type_name ;

element type definition ::=

cursor_name db_table_name

% ROWTYPE

column_name % TYPE

% TYPE object_name

REF object_type_name

field_name record_name % TYPE record_type_name scalar_datatype_name variable_name % TYPE

Keyword and Parameter Description

element_type

The type of PL/SQL collection element. The type can be any PL/SQL datatype except

REF CURSOR

INDEX BY type_name

Optional. Defines an associative array, where you specify the subscript values to use rather than the system defining them in sequence. type_name

can be

BINARY_INTEGER

PLS_INTEGER

, or

VARCHAR2

, or one of

VARCHAR2

subtypes

VARCHAR

STRING

, or

LONG

. v_size

specifies the length of the

VARCHAR2

key.

size_limit

A positive integer literal that specifies the maximum size of a varray, which is the maximum number of elements the varray can contain. Note that a maximum limit is imposed. See

"Choosing Between Nested Tables and Associative Arrays" on page 5-5.

type_name

A user-defined collection type that was defined using the datatype specifier

TABLE

VARRAY

Usage Notes

Nested tables extend the functionality of associative arrays (formerly known as index-by tables), so they differ in several ways. See

Every element reference includes the collection name and one or more subscripts enclosed in parentheses; the subscripts determine which element is processed. Except

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Oracle Database PL/SQL User’s Guide and Reference

Collection Definition for associative arrays, which can have negative subscripts, collection subscripts have a fixed lower bound of 1. Subscripts for multilevel collections are evaluated in any order; if a subscript includes an expression that modifies the value of a different subscript, the result is undefined. See

Collections" on page 5-16.

You can define all three collection types in the declarative part of any PL/SQL block, subprogram, or package. But, only nested table and varray types can be created and stored in an Oracle database.

Associative arrays and nested tables can be sparse (have non-consecutive subscripts), but varrays are always dense (have consecutive subscripts). Unlike nested tables, varrays retain their ordering and subscripts when stored in the database. Initially, associative arrays are sparse. That enables you, for example, to store reference data in a temporary variable using a primary key (account numbers or employee numbers for example) as the index.

Collections follow the usual scoping and instantiation rules. In a package, collections are instantiated when you first reference the package and cease to exist when you end the database session. In a block or subprogram, local collections are instantiated when you enter the block or subprogram and cease to exist when you exit.

Until you initialize it, a nested table or varray is atomically null (that is, the collection itself is null, not its elements). To initialize a nested table or varray, you use a constructor, which is a system-defined function with the same name as the collection type. This function constructs (creates) a collection from the elements passed to it.

For information on collection comparisons that are allowed, see

"Comparing

Collections can store instances of an object type and, conversely, can be attributes of an object type. Collections can also be passed as parameters. You can use them to move columns of data into and out of database tables or between client-side applications and stored subprograms.

When calling a function that returns a collection, you use the following syntax to reference elements in the collection: function_name(parameter_list)(subscript)

See

Example 5–16, "Referencing an Element of an Associative Array" on page 5-12 and

Example B–2, "Using the Dot Notation to Qualify Names" on page B-2.

With the Oracle Call Interface (OCI) or the Oracle Precompilers, you can bind host arrays to associative arrays (index-by tables) declared as the formal parameters of a subprogram. That lets you pass host arrays to stored functions and procedures.

Examples

For examples, see the following:

Example 5–1, "Declaring Collection Types" on page 5-3

Example 5–3, "Declaring Nested Tables, Varrays, and Associative Arrays" on page 5-7

Example 5–4, "Declaring Collections with %TYPE" on page 5-8

Example 5–5, "Declaring a Procedure Parameter as a Nested Table" on page 5-8

Example 5–42, "Declaring and Initializing Record Types" on page 5-29

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"Collection Methods" on page 13-20

"Object Type Declaration" on page 13-78

"Record Definition" on page 13-95

PL/SQL Language Elements

13-19

Collection Methods

A collection method is a built-in function or procedure that operates on collections and is called using dot notation. You can use the methods

EXISTS

COUNT

LIMIT

FIRST

LAST

PRIOR

EXTEND

TRIM

, and

DELETE

to manage collections whose size is unknown or varies.

EXISTS

COUNT

LIMIT

FIRST

LAST

PRIOR

, and

are functions that check the properties of a collection or individual collection elements.

EXTEND

TRIM

, and

DELETE

are procedures that modify a collection.

EXISTS

PRIOR

TRIM

EXTEND

, and

DELETE

take integer parameters.

EXISTS

PRIOR

, and

DELETE

can also take

VARCHAR2

parameters for associative arrays with string keys.

EXTEND

and

TRIM

cannot be used with index-by tables.

For more information, see

"Using Collection Methods" on page 5-19.

Syntax

collection call method ::=

COUNT

, index

( index

DELETE

EXISTS ( index )

)

, index collection_name .

( number

EXTEND

FIRST

LAST

LIMIT

NEXT ( index )

PRIOR (

( index ) number

TRIM

)

Keyword and Parameter Description

collection_name

An associative array, nested table, or varray previously declared within the current scope.

COUNT

R eturns the number of elements that a collection currently contains, which is useful because the current size of a collection is not always known. You can use

COUNT wherever an integer expression is allowed. For varrays,

COUNT

always equals

LAST

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Oracle Database PL/SQL User’s Guide and Reference

Collection Methods

For nested tables, normally,

COUNT

equals

LAST

. But, if you delete elements from the middle of a nested table,

COUNT

is smaller than

LAST

DELETE

This procedure has three forms.

DELETE

removes all elements from a collection.

DELETE(n)

removes the nth element from an associative array or nested table. If n

is null,

DELETE(n)

does nothing.

DELETE(m,n)

removes all elements in the range m..n

from an associative array or nested table. If m

is larger than n

or if m

or n

is null,

DELETE(m,n)

does nothing.

EXISTS

EXISTS(n)

returns

TRUE

if the nth element in a collection exists. Otherwise,

EXISTS(n)

returns

FALSE

. Mainly, you use

EXISTS

with

DELETE

to maintain sparse nested tables. You can also use

EXISTS

to avoid raising an exception when you reference a nonexistent element. When passed an out-of-range subscript,

EXISTS returns

FALSE

instead of raising

SUBSCRIPT_OUTSIDE_LIMIT

EXTEND

This procedure has three forms.

EXTEND

appends one null element to a collection.

EXTEND(n)

appends n

null elements to a collection.

EXTEND(n,i)

appends n

copies of the ith element to a collection.

EXTEND

operates on the internal size of a collection.

EXTEND

encounters deleted elements, it includes them in its tally. You cannot use

EXTEND

with associative arrays.

FIRST, LAST

FIRST

and

LAST

return the first and last (smallest and largest) subscript values in a collection. The subscript values are usually integers, but can also be strings for associative arrays. If the collection is empty,

FIRST

and

LAST

return

NULL

. If the collection contains only one element,

FIRST

and

LAST

return the same subscript value. For varrays,

FIRST

always returns 1 and

LAST

always equals

COUNT

. For nested tables, normally,

LAST

equals

COUNT

. But, if you delete elements from the middle of a nested table,

LAST

is larger than

COUNT

index

An expression that must return (or convert implicitly to) an integer in most cases, or a string for an associative array declared with string keys.

LIMIT

For nested tables, which have no maximum size,

LIMIT

returns

NULL

. For varrays,

LIMIT

returns the maximum number of elements that a varray can contain (which you must specify in its type definition).

NEXT, PRIOR

PRIOR(n)

returns the subscript that precedes index n

in a collection.

NEXT(n)

returns the subscript that succeeds index n

. If n

has no predecessor,

PRIOR(n)

returns

NULL

Likewise, if n

has no successor,

NEXT(n)

returns

NULL

TRIM

This procedure has two forms.

TRIM

removes one element from the end of a collection.

TRIM(n)

removes n

elements from the end of a collection. If n

is greater than

COUNT

TRIM(n)

raises

SUBSCRIPT_BEYOND_COUNT

. You cannot use

TRIM

with index-by

PL/SQL Language Elements

13-21

Collection Methods tables.

TRIM

operates on the internal size of a collection. If

TRIM

encounters deleted elements, it includes them in its tally.

Usage Notes

You cannot use collection methods in a SQL statement. If you try, you get a compilation error.

Only

EXISTS

can be applied to atomically null collections. If you apply another method to such collections, PL/SQL raises

COLLECTION_IS_NULL

If the collection elements have sequential subscripts, you can use collection.FIRST

.. collection.LAST

in a

FOR

loop to iterate through all the elements. You can use

PRIOR

to traverse collections indexed by any series of subscripts. For example, you can use

PRIOR

to traverse a nested table from which some elements have been deleted, or an associative array where the subscripts are string values.

EXTEND

operates on the internal size of a collection, which includes deleted elements.

You cannot use

EXTEND

to initialize an atomically null collection. Also, if you impose the

NOT NULL

constraint on a

TABLE

VARRAY

type, you cannot apply the first two forms of

EXTEND

to collections of that type.

If an element to be deleted does not exist,

DELETE

simply skips it; no exception is raised. Varrays are dense, so you cannot delete their individual elements. Because

PL/SQL keeps placeholders for deleted elements, you can replace a deleted element by assigning it a new value. However, PL/SQL does not keep placeholders for trimmed elements.

The amount of memory allocated to a nested table can increase or decrease dynamically. As you delete elements, memory is freed page by page. If you delete the entire table, all the memory is freed.

In general, do not depend on the interaction between

TRIM

and

DELETE

. It is better to treat nested tables like fixed-size arrays and use only

DELETE

, or to treat them like stacks and use only

TRIM

and

EXTEND

Within a subprogram, a collection parameter assumes the properties of the argument bound to it. You can apply methods

FIRST

LAST

COUNT

, and so on to such parameters. For varray parameters, the value of

LIMIT

is always derived from the parameter type definition, regardless of the parameter mode.

Examples

For examples, see the following:

Example 5–28, "Checking Whether a Collection Element EXISTS" on page 5-20

Example 5–29, "Counting Collection Elements With COUNT" on page 5-20

Example 5–30, "Checking the Maximum Size of a Collection With LIMIT" on page 5-21

Example 5–31, "Using FIRST and LAST With a Collection" on page 5-21

Example 5–32, "Using PRIOR and NEXT to Access Collection Elements" on page 5-22

Example 5–34, "Using EXTEND to Increase the Size of a Collection" on page 5-23

Example 5–35, "Using TRIM to Decrease the Size of a Collection" on page 5-24

Example 5–37, "Using the DELETE Method on a Collection" on page 5-26

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"Collection Definition" on page 13-17

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Oracle Database PL/SQL User’s Guide and Reference

Comments

Comments let you include arbitrary text within your code to explain what the code does. You can also disable obsolete or unfinished pieces of code by turning them into comments.

PL/SQL supports two comment styles: single-line and multi-line. A double hyphen

(

- -

) anywhere on a line (except within a character literal) turns the rest of the line into a comment. Multi-line comments begin with a slash-asterisk (

) and end with an asterisk-slash (

). For more information, see "Comments" on page 2-7.

Syntax

comment ::=

–– text

/* text */

Usage Notes

While testing or debugging a program, you might want to disable lines of code.

Single-line comments can appear within a statement at the end of a line. You can include single-line comments inside multi-line comments, but you cannot nest multi-line comments.

You cannot use single-line comments in a PL/SQL block that will be processed dynamically by an Oracle Precompiler program. End-of-line characters are ignored, making the single-line comments extend to the end of the block. Instead, use multi-line comments. You can use multi-line comment delimiters to comment-out whole sections of code.

Examples

For examples, see the following:

Example 2–4, "Using Single-Line Comments" on page 2-7

Example 2–5, "Using Multi-Line Comments" on page 2-8

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

PL/SQL Language Elements

13-23

COMMIT Statement

The

COMMIT

statement makes permanent any changes made to the database during the current transaction. A commit also makes the changes visible to other users. For

more information on PL/SQL transaction processing, see "Overview of Transaction

Processing in PL/SQL" on page 6-30.

The SQL

COMMIT

statement can be embedded as static SQL in PL/SQL. For syntax details on the SQL

COMMIT

statement, see the Oracle Database SQL Reference. See also

"Committing Transactions" in Oracle Database Application Developer's Guide -

Fundamentals and the

COMMIT_WRITE

initialization parameter in Oracle Database

Reference.

Usage Notes

The

COMMIT

statement releases all row and table locks, and erases any savepoints you marked since the last commit or rollback. Until your changes are committed:

■

You can see the changes when you query the tables you modified, but other users cannot see the changes.

■

If you change your mind or need to correct a mistake, you can use the

ROLLBACK statement to roll back (undo) the changes.

If you commit while a

FOR UPDATE

cursor is open, a subsequent fetch on that cursor raises an exception. The cursor remains open, so you should still close it. For more

information, see "Using FOR UPDATE" on page 6-34.

Examples

For examples, see the following:

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

Example 6–3, "Substituting PL/SQL Variables" on page 6-2

Example 6–36, "Using COMMIT With the WRITE Clause" on page 6-30

Example 6–40, "Using SET TRANSACTION to Begin a Read-only Transaction" on page 6-33

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Related Topics

"SAVEPOINT Statement" on page 13-106

"Transaction Control" on page 6-3

"Fetching Across Commits" on page 6-35

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Oracle Database PL/SQL User’s Guide and Reference

Constant and Variable Declaration

You can declare constants and variables in the declarative part of any PL/SQL block, subprogram, or package. Declarations allocate storage for a value, specify its datatype, and specify a name that you can reference. Declarations can also assign an initial value and impose the

NOT NULL

constraint. For more information, see Declarations on page 2-8.

Syntax

variable declaration ::=

NOT NULL

DEFAULT expression variable_name datatype ;

datatype ::=

collection_name % collection_type_name

TYPE cursor_name % ROWTYPE cursor_variable_name % TYPE

% ROWTYPE db_table_name

column_name % TYPE object_name

REF

% TYPE record_name % record_type_name object_type_name

TYPE ref_cursor_type_name scalar_datatype_name variable_name % TYPE

constant ::=

constant_name CONSTANT datatype

NOT NULL

DEFAULT expression ;

PL/SQL Language Elements

13-25

Constant and Variable Declaration

Keyword and Parameter Description

collection_name

A collection (associative array, nested table, or varray) previously declared within the current scope.

collection_type_name

A user-defined collection type defined using the datatype specifier

TABLE

VARRAY

CONSTANT

Denotes the declaration of a constant. You must initialize a constant in its declaration.

Once initialized, the value of a constant cannot be changed.

constant_name

A program constant. For naming conventions, see "Identifiers" on page 2-3.

cursor_name

An explicit cursor previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable previously declared within the current scope.

db_table_name

A database table or view that must be accessible when the declaration is elaborated.

db_table_name.column_name

A database table and column that must be accessible when the declaration is elaborated.

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the declaration is elaborated, the value of expression

is assigned to the constant or variable. The value and the constant or variable must have compatible datatypes.

NOT NULL

A constraint that prevents the program from assigning a null value to a variable or constant. Assigning a null to a variable defined as

NOT NULL

raises the predefined exception

VALUE_ERROR

. The constraint

NOT NULL

must be followed by an initialization clause.

object_name

An instance of an object type previously declared within the current scope.

record_name

A user-defined or

%ROWTYPE

record previously declared within the current scope.

record_name.field_name

A field in a user-defined or

%ROWTYPE

record previously declared within the current scope.

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Constant and Variable Declaration

record_type_name

A user-defined record type that is defined using the datatype specifier

RECORD

ref_cursor_type_name

A user-defined cursor variable type, defined using the datatype specifier

REF CURSOR

%ROWTYPE

Represents a record that can hold a row from a database table or a cursor. Fields in the record have the same names and datatypes as columns in the row.

scalar_datatype_name

A predefined scalar datatype such as

BOOLEAN

NUMBER

, or

VARCHAR2

. Includes any qualifiers for size, precision, or character versus byte semantics.

%TYPE

Represents the datatype of a previously declared collection, cursor variable, field, object, record, database column, or variable.

variable_name

A program variable.

Usage Notes

Constants and variables are initialized every time a block or subprogram is entered. By default, variables are initialized to

NULL

. Whether public or private, constants and variables declared in a package spec are initialized only once for each session.

An initialization clause is required when declaring

NOT NULL

variables and when declaring constants. If you use

%ROWTYPE

to declare a variable, initialization is not allowed.

You can define constants of complex types that have no literal values or predefined constructors, by calling a function that returns a filled-in value. For example, you can make a constant associative array this way.

Examples

For examples, see the following:

Example 1–1, "Declaring Variables in PL/SQL" on page 1-5

Example 1–2, "Assigning Values to Variables With the Assignment Operator" on page 1-6

Example 1–3, "Assigning Values to Variables by SELECTing INTO" on page 1-6

Example 2–9, "Using the %ROWTYPE Attribute" on page 2-11

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"Declaring Variables" on page 1-5

"Declarations" on page 2-8

"Overview of Predefined PL/SQL Datatypes" on page 3-1

"Assignment Statement" on page 13-3

"%ROWTYPE Attribute" on page 13-104

"%TYPE Attribute" on page 13-119

PL/SQL Language Elements

13-27

Cursor Attributes

Every explicit cursor and cursor variable has four attributes:

%FOUND

%ISOPEN

%NOTFOUND

, and

%ROWCOUNT

. When appended to the cursor or cursor variable, these attributes return useful information about the execution of a data manipulation statement. For more information, see

"Using Cursor Expressions" on page 6-28.

The implicit cursor

SQL

has additional attributes,

%BULK_ROWCOUNT

and

%BULK_EXCEPTIONS

. For more information, see

"SQL Cursor" on page 13-115.

Syntax

cursor attribute ::=

cursor_name cursor_variable_name

: host_cursor_variable_name

FOUND

ISOPEN

NOTFOUND

ROWCOUNT

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable (or parameter) previously declared within the current scope.

%FOUND Attribute

A cursor attribute that can be appended to the name of a cursor or cursor variable.

Before the first fetch from an open cursor, cursor_name%FOUND

returns

NULL

Afterward, it returns

TRUE

if the last fetch returned a row, or

FALSE

if the last fetch failed to return a row.

host_cursor_variable_name

%ISOPEN Attribute

A cursor attribute that can be appended to the name of a cursor or cursor variable. If a cursor is open, cursor_name%ISOPEN

returns

TRUE

; otherwise, it returns

FALSE

%NOTFOUND Attribute

A cursor attribute that can be appended to the name of a cursor or cursor variable.

Before the first fetch from an open cursor, cursor_name%NOTFOUND

returns

NULL

Thereafter, it returns

FALSE

if the last fetch returned a row, or

TRUE

if the last fetch failed to return a row.

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Cursor Attributes

%ROWCOUNT Attribute

A cursor attribute that can be appended to the name of a cursor or cursor variable.

When a cursor is opened,

%ROWCOUNT

is zeroed. Before the first fetch, cursor_name%ROWCOUNT

returns 0. Thereafter, it returns the number of rows fetched so far. The number is incremented if the latest fetch returned a row.

Usage Notes

The cursor attributes apply to every cursor or cursor variable. For example, you can open multiple cursors, then use

%FOUND

%NOTFOUND

to tell which cursors have rows left to fetch. Likewise, you can use

%ROWCOUNT

to tell how many rows have been fetched so far.

If a cursor or cursor variable is not open, referencing it with

%FOUND

%NOTFOUND

, or

%ROWCOUNT

raises the predefined exception

INVALID_CURSOR

When a cursor or cursor variable is opened, the rows that satisfy the associated query are identified and form the result set. Rows are fetched from the result set one at a time.

If a

SELECT INTO

statement returns more than one row, PL/SQL raises the predefined exception

TOO_MANY_ROWS

and sets

%ROWCOUNT

to 1, not the actual number of rows that satisfy the query.

Before the first fetch,

%NOTFOUND

evaluates to

NULL

. If

FETCH

never executes successfully, the

EXIT WHEN

condition is never

TRUE

and the loop is never exited. To be safe, you might want to use the following

EXIT

statement instead:

EXIT WHEN c1%NOTFOUND OR c1%NOTFOUND IS NULL;

You can use the cursor attributes in procedural statements, but not in SQL statements.

Examples

For examples, see the following:

Example 6–8, "Using SQL%ROWCOUNT" on page 6-7

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–15, "Using %ISOPEN" on page 6-12

Related Topics

"Managing Cursors in PL/SQL" on page 6-6

PL/SQL Language Elements

13-29

Cursor Variables

To execute a multi-row query, Oracle opens an unnamed work area that stores processing information. You can access this area through an explicit cursor, which names the work area, or through a cursor variable, which points to the work area. To create cursor variables, you define a

REF CURSOR

type, then declare cursor variables of that type.

Cursor variables are like C or Pascal pointers, which hold the address of some item instead of the item itself. Declaring a cursor variable creates a pointer, not an item.

For more information, see

"Using Cursor Variables (REF CURSORs)" on page 6-20.

Syntax

ref cursor type definition ::=

TYPE type_name IS REF CURSOR

RETURN db_table_name cursor_name cursor_variable_name record_name % TYPE

% record_type_name ref_cursor_type_name

ROWTYPE

;

ref cursor variable declaration ::=

cursor_variable_name type_name ;

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable previously declared within the current scope.

db_table_name

A database table or view, which must be accessible when the declaration is elaborated.

record_name

A user-defined record previously declared within the current scope.

record_type_name

A user-defined record type that was defined using the datatype specifier

RECORD

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Oracle Database PL/SQL User’s Guide and Reference

Cursor Variables

REF CURSOR

Cursor variables all have the datatype

REF CURSOR

RETURN

Specifies the datatype of a cursor variable return value. You can use the

%ROWTYPE attribute in the

RETURN

clause to provide a record type that represents a row in a database table, or a row from a cursor or strongly typed cursor variable. You can use the

%TYPE

attribute to provide the datatype of a previously declared record.

%ROWTYPE

A record type that represents a row in a database table or a row fetched from a cursor or strongly typed cursor variable. Fields in the record and corresponding columns in the row have the same names and datatypes.

%TYPE

Provides the datatype of a previously declared user-defined record.

type_name

A user-defined cursor variable type that was defined as a

REF CURSOR

Usage Notes

Cursor variables are available to every PL/SQL client. For example, you can declare a cursor variable in a PL/SQL host environment such as an OCI or Pro*C program, then pass it as a bind variable to PL/SQL. Application development tools that have a

PL/SQL engine can use cursor variables entirely on the client side.

You can pass cursor variables back and forth between an application and the database server through remote procedure calls using a database link. If you have a PL/SQL engine on the client side, you can use the cursor variable in either location. For example, you can declare a cursor variable on the client side, open and fetch from it on the server side, then continue to fetch from it back on the client side.

You use cursor variables to pass query result sets between PL/SQL stored subprograms and client programs. Neither PL/SQL nor any client program owns a result set; they share a pointer to the work area where the result set is stored. For example, an OCI program, Oracle Forms application, and the database can all refer to the same work area.

REF CURSOR

types can be strong or weak. A strong

REF CURSOR

type definition specifies a return type, but a weak definition does not. Strong

REF CURSOR

types are less error-prone because PL/SQL lets you associate a strongly typed cursor variable only with type-compatible queries. Weak

REF CURSOR

types are more flexible because you can associate a weakly typed cursor variable with any query.

Once you define a

REF CURSOR

type, you can declare cursor variables of that type. You can use

%TYPE

to provide the datatype of a record variable. Also, in the

RETURN

clause of a

REF CURSOR

type definition, you can use

%ROWTYPE

to specify a record type that represents a row returned by a strongly (not weakly) typed cursor variable.

Currently, cursor variables are subject to several restrictions. See

"Restrictions on

Cursor Variables" on page 6-27.

You use three statements to control a cursor variable:

OPEN

FOR

FETCH

, and

First, you

OPEN

a cursor variable

FOR

a multi-row query. Then, you

FETCH

rows from the result set. When all the rows are processed, you

the cursor variable.

PL/SQL Language Elements

13-31

Cursor Variables

Other

OPEN

FOR

statements can open the same cursor variable for different queries.

You need not close a cursor variable before reopening it. When you reopen a cursor variable for a different query, the previous query is lost.

PL/SQL makes sure the return type of the cursor variable is compatible with the

INTO clause of the

FETCH

statement. For each column value returned by the query associated with the cursor variable, there must be a corresponding, type-compatible field or variable in the

INTO

clause. Also, the number of fields or variables must equal the number of column values. Otherwise, you get an error.

If both cursor variables involved in an assignment are strongly typed, they must have the same datatype. However, if one or both cursor variables are weakly typed, they need not have the same datatype.

When declaring a cursor variable as the formal parameter of a subprogram that fetches from or closes the cursor variable, you must specify the

IN OUT

mode. If the subprogram opens the cursor variable, you must specify the

IN OUT

mode.

Be careful when passing cursor variables as parameters. At run time, PL/SQL raises

ROWTYPE_MISMATCH

if the return types of the actual and formal parameters are incompatible.

You can apply the cursor attributes

%FOUND

%NOTFOUND

%ISOPEN

, and

%ROWCOUNT to a cursor variable.

If you try to fetch from, close, or apply cursor attributes to a cursor variable that does not point to a query work area, PL/SQL raises the predefined exception

INVALID_CURSOR

. You can make a cursor variable (or parameter) point to a query work area in two ways:

■

OPEN

the cursor variable

FOR

the query.

Assign to the cursor variable the value of an already

OPEN ed host cursor variable or PL/SQL cursor variable.

A query work area remains accessible as long as any cursor variable points to it.

Therefore, you can pass the value of a cursor variable freely from one scope to another.

For example, if you pass a host cursor variable to a PL/SQL block embedded in a

Pro*C program, the work area to which the cursor variable points remains accessible after the block completes.

Examples

For examples, see the following:

Example 6–9, "Declaring a Cursor" on page 6-9

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 6–27, "Passing a REF CURSOR as a Parameter" on page 6-22

Example 6–29, "Stored Procedure to Open a Ref Cursor" on page 6-23

Example 6–30, "Stored Procedure to Open Ref Cursors with Different Queries" on page 6-23

Example 6–31, "Cursor Variable with Different Return Types" on page 6-24

Related Topics

"Cursor Attributes" on page 13-28

"Constant and Variable Declaration" on page 13-25.

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Oracle Database PL/SQL User’s Guide and Reference

Cursor Declaration

To execute a multi-row query, Oracle opens an unnamed work area that stores processing information. A cursor lets you name the work area, access the information, and process the rows individually. For more information, see

"Querying Data with

PL/SQL" on page 6-14.

Syntax

cursor declaration ::=

( cursor_parameter_declaration )

CURSOR cursor_name

RETURN rowtype

IS select_statement ;

cursor spec ::=

( cursor_parameter_declaration

CURSOR cursor_name

RETURN rowtype ;

cursor body ::=

( cursor_parameter_declaration

CURSOR cursor_name

RETURN rowtype IS select_statement ;

cursor parameter declaration ::=

DEFAULT expression parameter_name datatype

)

PL/SQL Language Elements

13-33

Cursor Declaration

rowtype ::=

db_table_name cursor_name cursor_variable_name record_name % TYPE record_type_name

% ROWTYPE

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope.

datatype

A type specifier. For the syntax of datatype

, see

db_table_name

A database table or view that must be accessible when the declaration is elaborated.

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the declaration is elaborated, the value of expression

is assigned to the parameter. The value and the parameter must have compatible datatypes.

parameter_name

A variable declared as the formal parameter of a cursor. A cursor parameter can appear in a query wherever a constant can appear. The formal parameters of a cursor must be

parameters. The query can also reference other PL/SQL variables within its scope.

record_name

A user-defined record previously declared within the current scope.

record_type_name

A user-defined record type that was defined using the datatype specifier

RECORD

RETURN

Specifies the datatype of a cursor return value. You can use the

%ROWTYPE

attribute in the

RETURN

clause to provide a record type that represents a row in a database table or a row returned by a previously declared cursor. Also, you can use the

%TYPE

attribute to provide the datatype of a previously declared record.

A cursor body must have a

SELECT

statement and the same

RETURN

clause as its corresponding cursor spec. Also, the number, order, and datatypes of select items in the

SELECT

clause must match the

RETURN

clause.

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Cursor Declaration

%ROWTYPE

A record type that represents a row in a database table or a row fetched from a previously declared cursor or cursor variable. Fields in the record and corresponding columns in the row have the same names and datatypes.

select_statement

A query that returns a result set of rows. Its syntax is like that of select_into_statement

without the

INTO

clause. See

"SELECT INTO Statement" on page 13-107. If the cursor declaration declares parameters, each parameter must be

used in the query.

%TYPE

Provides the datatype of a previously declared user-defined record.

Usage Notes

You must declare a cursor before referencing it in an

OPEN

FETCH

, or

CLOSE statement. You must declare a variable before referencing it in a cursor declaration.

The word SQL is reserved by PL/SQL as the default name for implicit cursors, and cannot be used in a cursor declaration.

You cannot assign values to a cursor name or use it in an expression. However, cursors and variables follow the same scoping rules. For more information, see

"Scope and

Visibility of PL/SQL Identifiers" on page 2-15.

You retrieve data from a cursor by opening it, then fetching from it. Because the

FETCH statement specifies the target variables, using an

INTO

clause in the

SELECT

statement of a cursor_declaration

is redundant and invalid.

The scope of cursor parameters is local to the cursor, meaning that they can be referenced only within the query used in the cursor declaration. The values of cursor parameters are used by the associated query when the cursor is opened. The query can also reference other PL/SQL variables within its scope.

The datatype of a cursor parameter must be specified without constraints, that is, without precision and scale for numbers, and without length for strings.

Examples

For examples, see the following:

Example 6–9, "Declaring a Cursor" on page 6-9

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 6–27, "Passing a REF CURSOR as a Parameter" on page 6-22

Example 6–29, "Stored Procedure to Open a Ref Cursor" on page 6-23

Example 6–30, "Stored Procedure to Open Ref Cursors with Different Queries" on page 6-23

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"Declaring a Cursor" on page 6-8

PL/SQL Language Elements

13-35

DELETE Statement

The

DELETE

statement removes entire rows of data from a specified table or view. For a full description of the

DELETE

statement, see Oracle Database SQL Reference.

Syntax

delete ::=

DELETE

FROM table_reference

( subquery

TABLE (

) subquery2 ) alias

WHERE search_condition

CURRENT_OF cursor_name returning_clause

;

table_reference ::=

schema .

table_name view_name

@ dblink

Keyword and Parameter Description

alias

Another (usually short) name for the referenced table or view. Typically referred to later in the

WHERE

clause.

BULK COLLECT

Returns columns from the deleted rows into PL/SQL collections, as specified by the

RETURNING INTO

list. The corresponding columns must store scalar (not composite)

values. For more information, see "Reducing Loop Overhead for DML Statements and

Queries with Bulk SQL" on page 11-8.

returning_clause

Returns values from the deleted rows, eliminating the need to

SELECT

the rows first.

You can retrieve the column values into individual variables or into collections. You cannot use the

RETURNING

clause for remote or parallel deletes. If the statement does not affect any rows, the values of the variables specified in the

RETURNING

clause are

undefined. See "RETURNING INTO Clause" on page 13-101.

subquery

SELECT

statement that provides a set of rows for processing. Its syntax is like the select_into_statement

without the

INTO

clause. See

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

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Oracle Database PL/SQL User’s Guide and Reference

DELETE Statement

table_reference

A table or view, which must be accessible when you execute the

DELETE

statement, and for which you must have

DELETE

privileges.

TABLE (subquery2)

The operand of

TABLE

is a

SELECT

statement that returns a single column value, which must be a nested table. Operator

TABLE

informs Oracle that the value is a collection, not a scalar value.

WHERE CURRENT OF cursor_name

Refers to the latest row processed by the

FETCH

statement associated with the cursor identified by cursor_name

. The cursor must be

FOR UPDATE

and must be open and positioned on a row. If the cursor is not open, the

CURRENT OF

clause causes an error.

If the cursor is open, but no rows have been fetched or the last fetch returned no rows,

PL/SQL raises the predefined exception

NO_DATA_FOUND

WHERE search_condition

Conditionally chooses rows to be deleted from the referenced table or view. Only rows that meet the search condition are deleted. If you omit the

WHERE

clause, all rows in the table or view are deleted.

Usage Notes

You can use the

DELETE WHERE CURRENT OF

statement after a fetch from an open cursor (this includes implicit fetches executed in a cursor

FOR

loop), provided the associated query is

FOR UPDATE

. This statement deletes the current row; that is, the one just fetched.

The implicit cursor

SQL

and the cursor attributes

%NOTFOUND

%FOUND

, and

%ROWCOUNT

let you access useful information about the execution of a

DELETE statement.

Examples

For examples, see the following:

Example 6–5, "Using CURRVAL and NEXTVAL" on page 6-4

Example 6–8, "Using SQL%ROWCOUNT" on page 6-7

Example 6–29, "Stored Procedure to Open a Ref Cursor" on page 6-23

Example 6–30, "Stored Procedure to Open Ref Cursors with Different Queries" on page 6-23

Example 11–2, "Issuing DELETE Statements in a Loop" on page 11-9

Example 11–16, "Using FORALL With BULK COLLECT" on page 11-19

Related Topics

"INSERT Statement" on page 13-66

"UPDATE Statement" on page 13-121

PL/SQL Language Elements

13-37

EXCEPTION_INIT Pragma

The pragma

EXCEPTION_INIT

associates an exception name with an Oracle error number. You can intercept any ORA- error and write a specific handler for it instead of using the

OTHERS

handler. For more information, see "Associating a PL/SQL

Exception with a Number: Pragma EXCEPTION_INIT" on page 10-7.

Syntax

exception_init pragma ::=

PRAGMA EXCEPTION_INIT ( exception_name , error_number ) ;

Keyword and Parameter Description

error_number

Any valid Oracle error number. These are the same error numbers (always negative) returned by the function

SQLCODE

exception_name

A user-defined exception declared within the current scope.

PRAGMA

Signifies that the statement is a compiler directive.

Usage Notes

You can use

EXCEPTION_INIT

in the declarative part of any PL/SQL block, subprogram, or package. The pragma must appear in the same declarative part as its associated exception, somewhere after the exception declaration.

Be sure to assign only one exception name to an error number.

Examples

For examples, see the following:

Example 10–4, "Using PRAGMA EXCEPTION_INIT" on page 10-7

Example 11–9, "Bulk Operation That Continues Despite Exceptions" on page 11-15

"SQLCODE Function" on page 13-117

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Oracle Database PL/SQL User’s Guide and Reference

Exception Definition

An exception is a runtime error or warning condition, which can be predefined or user-defined. Predefined exceptions are raised implicitly (automatically) by the runtime system. User-defined exceptions must be raised explicitly by

RAISE statements. To handle raised exceptions, you write separate routines called exception

handlers. For more information, see Chapter 10, "Handling PL/SQL Errors" .

Syntax

exception ::=

exception_name EXCEPTION ;

exception handler ::=

WHEN exception_name

OTHERS

OR exception_name

THEN statement

Keyword and Parameter Description

exception_name

A predefined exception such as

ZERO_DIVIDE

, or a user-defined exception previously declared within the current scope.

OTHERS

Stands for all the exceptions not explicitly named in the exception-handling part of the block. The use of

OTHERS

is optional and is allowed only as the last exception handler.

You cannot include

OTHERS

in a list of exceptions following the keyword

WHEN

statement

An executable statement. For the syntax of statement

, see "Block Declaration" on page 13-8.

WHEN

Introduces an exception handler. You can have multiple exceptions execute the same sequence of statements by following the keyword

WHEN

with a list of the exceptions, separating them by the keyword

. If any exception in the list is raised, the associated statements are executed.

Usage Notes

An exception declaration can appear only in the declarative part of a block, subprogram, or package. The scope rules for exceptions and variables are the same.

But, unlike variables, exceptions cannot be passed as parameters to subprograms.

Some exceptions are predefined by PL/SQL. For a list of these exceptions, see

"Summary of Predefined PL/SQL Exceptions" on page 10-4. PL/SQL declares

PL/SQL Language Elements

13-39

Exception Definition predefined exceptions globally in package

STANDARD

, so you need not declare them yourself.

Redeclaring predefined exceptions is error prone because your local declaration overrides the global declaration. In such cases, you must use dot notation to specify the predefined exception, as follows:

EXCEPTION

WHEN invalid_number OR STANDARD.INVALID_NUMBER THEN ...

The exception-handling part of a PL/SQL block is optional. Exception handlers must come at the end of the block. They are introduced by the keyword

EXCEPTION

. The exception-handling part of the block is terminated by the same keyword

END

that terminates the entire block. An exception handler can reference only those variables that the current block can reference.

An exception should be raised only when an error occurs that makes it undesirable or impossible to continue processing. If there is no exception handler in the current block for a raised exception, the exception propagates according to the following rules:

■

If there is an enclosing block for the current block, the exception is passed on to that block. The enclosing block then becomes the current block. If a handler for the raised exception is not found, the process repeats.

If there is no enclosing block for the current block, an unhandled exception error is passed back to the host environment.

Only one exception at a time can be active in the exception-handling part of a block.

Therefore, if an exception is raised inside a handler, the block that encloses the current block is the first block searched to find a handler for the newly raised exception. From there on, the exception propagates normally.

Example

For examples, see the following:

Example 1–9, "Using WHILE-LOOP for Control" on page 1-11

Example 1–12, "Creating a Stored Subprogram" on page 1-13

Example 2–19, "PL/SQL Block Using Multiple and Duplicate Labels" on page 2-17

Example 5–35, "Using TRIM to Decrease the Size of a Collection" on page 5-24

Example 5–38, "Collection Exceptions" on page 5-27

Example 8–1, "Simple PL/SQL Procedure" on page 8-2

Example 9–3, "Creating the emp_admin Package" on page 9-6

Example 10–1, "Runtime Error Handling" on page 10-2

Example 10–3, "Scope of PL/SQL Exceptions" on page 10-6

Example 10–9, "Reraising a PL/SQL Exception" on page 10-12

Example 11–6, "Using Rollbacks With FORALL" on page 11-12

Example 11–9, "Bulk Operation That Continues Despite Exceptions" on page 11-15

Example 12–3, "Null Objects in a PL/SQL Block" on page 12-3

Related Topics

"Block Declaration" on page 13-8

"RAISE Statement" on page 13-94

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Oracle Database PL/SQL User’s Guide and Reference

EXECUTE IMMEDIATE Statement

The

EXECUTE IMMEDIATE

statement executes a dynamic SQL statement or anonymous PL/SQL block. You can use it to issue SQL statements that cannot be represented directly in PL/SQL, or to build up statements where you do not know all the table names, WHERE clauses, and so on in advance. For more information, see

"Using the EXECUTE IMMEDIATE Statement in PL/SQL" on page 7-2.

Syntax

EXECUTE_IMMEDIATE dynamic_string

INTO

, define_variable record_name

BULK COLLECT INTO

, collection_name host_array_name

OUT

IN OUT

, bind_argument

USING returning_clause ;

Keyword and Parameter Description

bind_argument

An expression whose value is passed to the dynamic SQL statement, or a variable that stores a value returned by the dynamic SQL statement.

BULK COLLECT

Stores result values in one or more collections, for faster queries than loops with

FETCH

statements. For more information, see

Statements and Queries with Bulk SQL" on page 11-8.

collection_name

A declared collection into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible collection in the list.

PL/SQL Language Elements

13-41

EXECUTE IMMEDIATE Statement

host_array_name

An array (declared in a PL/SQL host environment and passed to PL/SQL as a bind variable) into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible array in the list. Host arrays must be prefixed with a colon.

define_variable

A variable that stores a selected column value.

dynamic_string

A string literal, variable, or expression that represents a single SQL statement or a

PL/SQL block. It must be of type

CHAR

VARCHAR2

, not

NCHAR

NVARCHAR2

INTO ...

Used only for single-row queries, this clause specifies the variables or record into which column values are retrieved. For each value retrieved by the query, there must be a corresponding, type-compatible variable or field in the

INTO

clause.

record_name

A user-defined or

%ROWTYPE

record that stores a selected row.

returning_clause

Returns values from inserted rows, eliminating the need to

SELECT

the rows afterward. You can retrieve the column values into variables or into collections. You cannot use the

RETURNING

clause for remote or parallel inserts. If the statement does not affect any rows, the values of the variables specified in the

RETURNING

clause are undefined. For the syntax of returning_clause

, see the

"RETURNING INTO

Clause" on page 13-101.

USING ...

Specifies a list of input and/or output bind arguments. The parameter mode defaults to

Usage Notes

Except for multi-row queries, the dynamic string can contain any SQL statement

(without the final semicolon) or any PL/SQL block (with the final semicolon). The string can also contain placeholders for bind arguments. You cannot use bind arguments to pass the names of schema objects to a dynamic SQL statement.

You can place all bind arguments in the

USING

clause. The default parameter mode is

. For DML statements that have a

RETURNING

clause, you can place

OUT

arguments in the

RETURNING INTO

clause without specifying the parameter mode, which, by definition, is

OUT

. If you use both the

USING

clause and the

RETURNING INTO

clause, the

USING

clause can contain only

arguments.

At run time, bind arguments replace corresponding placeholders in the dynamic string. Every placeholder must be associated with a bind argument in the

USING clause and/or

RETURNING INTO

clause. You can use numeric, character, and string literals as bind arguments, but you cannot use Boolean literals (

TRUE

FALSE

, and

NULL

). To pass nulls to the dynamic string, you must use a workaround. See

"Passing

Nulls to Dynamic SQL" on page 7-10.

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EXECUTE IMMEDIATE Statement

Dynamic SQL supports all the SQL datatypes. For example, define variables and bind arguments can be collections,

LOB s, instances of an object type, and refs. Dynamic SQL does not support PL/SQL-specific types. For example, define variables and bind arguments cannot be

BOOLEAN s or index-by tables. The only exception is that a

PL/SQL record can appear in the

INTO

clause.

You can execute a dynamic SQL statement repeatedly using new values for the bind arguments. You still incur some overhead, because

EXECUTE IMMEDIATE

re-prepares the dynamic string before every execution.

The string argument to the

EXECUTE IMMEDIATE

command cannot be one of the national character types, such as

NCHAR

NVARCHAR2

Note:

When using dynamic SQL with PL/SQL, be aware of the risks of SQL injection, which is a possible security issue. For more information on SQL injection and possible problems, see Oracle

Database Application Developer's Guide - Fundamentals. You can also search for "SQL injection" on the Oracle Technology Network at http://www.oracle.com/technology/

Examples

For examples, see the following:

Example 7–2, "Dynamic SQL Procedure that Accepts Table Name and WHERE Clause" on page 7-4

Example 7–4, "Dynamic SQL with BULK COLLECT INTO Clause" on page 7-6

Example 7–5, "Dynamic SQL with RETURNING BULK COLLECT INTO Clause" on page 7-6

Example 7–6, "Dynamic SQL Inside FORALL Statement" on page 7-7

Related Topics

"Controlling Loop Iterations: LOOP and EXIT Statements" on page 4-7.

PL/SQL Language Elements

13-43

EXIT Statement

The

EXIT

statement breaks out of a loop. The

EXIT

statement has two forms: the unconditional

EXIT

and the conditional

EXIT WHEN

. With either form, you can name the loop to be exited. For more information, see

Syntax

exit ::=

label_name WHEN boolean_expression

EXIT ;

Keyword and Parameter Description

boolean_expression

An expression that returns the Boolean value

TRUE

FALSE

, or

NULL

. It is evaluated with each iteration of the loop. If the expression returns

TRUE

, the current loop (or the loop labeled by label_name

) is exited immediately. For the syntax of boolean_expression

, see

"Expression Definition" on page 13-45.

EXIT

An unconditional

EXIT

statement (that is, one without a

WHEN

clause) exits the current loop immediately. Execution resumes with the statement following the loop.

label_name

Identifies the loop exit from: either the current loop, or any enclosing labeled loop.

Usage Notes

The

EXIT

statement can be used only inside a loop; you cannot exit from a block directly. PL/SQL lets you code an infinite loop. For example, the following loop will never terminate normally so you must use an

EXIT

statement to exit the loop.

WHILE TRUE LOOP ... END LOOP;

If you use an

EXIT

statement to exit a cursor

FOR

loop prematurely, the cursor is closed automatically. The cursor is also closed automatically if an exception is raised inside the loop.

Examples

For examples, see the following:

Example 4–8, "Using an EXIT Statement" on page 4-7

Example 4–17, "Using EXIT in a LOOP" on page 4-12

Example 4–18, "Using EXIT With a Label in a LOOP" on page 4-13

Related Topics

see "PL/SQL Expressions and Comparisons" on page 2-19.

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Expression Definition

An expression is an arbitrarily complex combination of variables, constants, literals, operators, and function calls. The simplest expression is a single variable.

The PL/SQL compiler determines the datatype of an expression from the types of the variables, constants, literals, and operators that comprise the expression. Every time the expression is evaluated, a single value of that type results. For more information,

Syntax

expression ::=

( boolean_expression character_expression date_expression numeric_expression

boolean_expression ::=

NOT boolean_constant_name boolean_function_call boolean_literal boolean_variable_name other_boolean_form

)

AND

NOT boolean_constant_name boolean_function_call boolean_literal boolean_variable_name other_boolean_form

PL/SQL Language Elements

13-45

Expression Definition

other boolean form ::=

collection_name .

cursor_name

SQL

EXISTS

: cursor_variable_name host_cursor_variable_name

(

% index relational_operator expression

NOT

IS NULL

)

FOUND

ISOPEN

NOTFOUND expression

NOT

LIKE pattern

BETWEEN expression AND expression

IN expression

character expression ::=

character_constant_name character_function_call character_literal character_variable_name

: host_variable_name

: indicator_name

|| character_constant_name character_function_call character_literal character_variable_name

: host_variable_name

: indicator_name

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numeric subexpression ::=

cursor_name cursor_variable_name

SQL host_cursor_variable_name

SQL % BULK_ROWCOUNT

: host_variable_name numeric_constant_name numeric_function_call numeric_literal numeric_variable_name collection_name .

COUNT

FIRST

LAST

LIMIT

PRIOR

( integer ) indicator_name

(

ROWCOUNT index )

date expression ::=

date_constant_name date_function_call date_literal date_variable_name

: host_variable_name

: indicator_name

– numeric_expression

** exponent

Expression Definition

PL/SQL Language Elements

13-47

Expression Definition

numeric expression ::=

–

* numeric_subexpression numeric_subexpression

Keyword and Parameter Description

BETWEEN

This comparison operator tests whether a value lies in a specified range. It means: greater than or equal to low value and less than or equal to high value.

boolean_constant_name

A constant of type

BOOLEAN

, which must be initialized to the value

TRUE

FALSE

, or

NULL

. Arithmetic operations on Boolean constants are not allowed.

boolean_expression

An expression that returns the Boolean value

TRUE

FALSE

, or

NULL

boolean_function_call

Any function call that returns a Boolean value.

boolean_literal

The predefined values

TRUE

FALSE

, or

NULL

(which stands for a missing, unknown, or inapplicable value). You cannot insert the value

TRUE

FALSE

into a database column.

boolean_variable_name

A variable of type

BOOLEAN

. Only the values

TRUE

FALSE

, and

NULL

can be assigned to a

BOOLEAN

variable. You cannot select or fetch column values into a

BOOLEAN variable. Also, arithmetic operations on

BOOLEAN

variables are not allowed.

%BULK_ROWCOUNT

Designed for use with the

FORALL

statement, this is a composite attribute of the implicit cursor

SQL

. For more information, see

"SQL Cursor" on page 13-115.

character_constant_name

A previously declared constant that stores a character value. It must be initialized to a character value or a value implicitly convertible to a character value.

character_expression

An expression that returns a character or character string.

character_function_call

A function call that returns a character value or a value implicitly convertible to a character value.

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Expression Definition

character_literal

A literal that represents a character value or a value implicitly convertible to a character value.

character_variable_name

A previously declared variable that stores a character value.

collection_name

A collection (nested table, index-by table, or varray) previously declared within the current scope.

cursor_name

An explicit cursor previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable previously declared within the current scope.

date_constant_name

A previously declared constant that stores a date value. It must be initialized to a date value or a value implicitly convertible to a date value.

date_expression

An expression that returns a date/time value.

date_function_call

A function call that returns a date value or a value implicitly convertible to a date value.

date_literal

A literal representing a date value or a value implicitly convertible to a date value.

date_variable_name

A previously declared variable that stores a date value.

EXISTS, COUNT, FIRST, LAST, LIMIT, NEXT, PRIOR

Collection methods. When appended to the name of a collection, these methods return useful information. For example,

EXISTS(n)

returns

TRUE

if the nth element of a collection exists. Otherwise,

EXISTS(n)

returns

FALSE

. For more information, see

"Collection Methods" on page 13-20.

exponent

An expression that must return a numeric value.

%FOUND, %ISOPEN, %NOTFOUND, %ROWCOUNT

Cursor attributes. When appended to the name of a cursor or cursor variable, these attributes return useful information about the execution of a multi-row query. You can also append them to the implicit cursor

SQL

PL/SQL Language Elements

13-49

Expression Definition

host_cursor_variable_name

A cursor variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. Host cursor variables must be prefixed with a colon.

host_variable_name

A variable declared in a PL/SQL host environment and passed to PL/SQL as a bind variable. The datatype of the host variable must be implicitly convertible to the appropriate PL/SQL datatype. Also, host variables must be prefixed with a colon.

IN

Comparison operator that tests set membership. It means: equal to any member of.

The set can contain nulls, but they are ignored. Also, expressions of the form value NOT IN set return

FALSE

if the set contains a null.

index

A numeric expression that must return a value of type

BINARY_INTEGER,

PLS_INTEGER

, or a value implicitly convertible to that datatype.

indicator_name

An indicator variable declared in a PL/SQL host environment and passed to PL/SQL.

Indicator variables must be prefixed with a colon. An indicator variable indicates the value or condition of its associated host variable. For example, in the Oracle

Precompiler environment, indicator variables can detect nulls or truncated values in output host variables.

IS NULL

Comparison operator that returns the Boolean value

TRUE

if its operand is null, or

FALSE

if its operand is not null.

LIKE

Comparison operator that compares a character value to a pattern. Case is significant.

returns the Boolean value

TRUE

if the character patterns match, or

FALSE

if they do not match.

NOT, AND, OR

Logical operators, which follow the tri-state logic of

Table 2–3 on page 2-20.

AND returns the value

TRUE

only if both its operands are true.

returns the value

TRUE

if either of its operands is true.

NOT

returns the opposite value (logical negation) of its operand. For more information, see

"Logical Operators" on page 2-20.

NULL

Keyword that represents a null. It stands for a missing, unknown, or inapplicable value. When

NULL

is used in a numeric or date expression, the result is a null.

numeric_constant_name

A previously declared constant that stores a numeric value. It must be initialized to a numeric value or a value implicitly convertible to a numeric value.

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Expression Definition

numeric_expression

An expression that returns an integer or real value.

numeric_function_call

A function call that returns a numeric value or a value implicitly convertible to a numeric value.

numeric_literal

A literal that represents a number or a value implicitly convertible to a number.

numeric_variable_name

A previously declared variable that stores a numeric value.

pattern

A character string compared by the

operator to a specified string value. It can include two special-purpose characters called wildcards. An underscore (_) matches exactly one character; a percent sign (%) matches zero or more characters. The pattern can be followed by

ESCAPE '

character_literal

, which turns off wildcard expansion wherever the escape character appears in the string followed by a percent sign or underscore.

relational_operator

Operator that compares expressions. For the meaning of each operator, see

"Comparison Operators" on page 2-22.

SQL

A cursor opened implicitly by Oracle to process a SQL data manipulation statement.

The implicit cursor

SQL

always refers to the most recently executed SQL statement.

+, -, /, *, **

Symbols for the addition, subtraction, division, multiplication, and exponentiation operators.

||

The concatenation operator. As the following example shows, the result of concatenating string1 with string2 is a character string that contains string1 followed by

string2:

'Good' || ' morning!' = 'Good morning!'

The next example shows that nulls have no effect on the result of a concatenation:

'suit' || NULL || 'case' = 'suitcase'

A null string (

), which is zero characters in length, is treated like a null.

Usage Notes

In a Boolean expression, you can only compare values that have compatible datatypes.

For more information, see

"Converting PL/SQL Datatypes" on page 3-21.

In conditional control statements, if a Boolean expression returns

TRUE

, its associated sequence of statements is executed. But, if the expression returns

FALSE

NULL

, its associated sequence of statements is not executed.

PL/SQL Language Elements

13-51

Expression Definition

The relational operators can be applied to operands of type

BOOLEAN

. By definition,

TRUE

is greater than

FALSE

. Comparisons involving nulls always return a null. The value of a Boolean expression can be assigned only to Boolean variables, not to host variables or database columns. Also, datatype conversion to or from type

BOOLEAN

is not supported.

You can use the addition and subtraction operators to increment or decrement a date value, as the following examples show: hire_date := '10-MAY-95'; hire_date := hire_date + 1; -- makes hire_date '11-MAY-95' hire_date := hire_date - 5; -- makes hire_date '06-MAY-95'

When PL/SQL evaluates a boolean expression,

NOT

has the highest precedence,

AND has the next-highest precedence, and

has the lowest precedence. However, you can use parentheses to override the default operator precedence.

Within an expression, operations occur in their predefined order of precedence. From first to last (top to bottom), the default order of operations is parentheses exponents unary operators multiplication and division addition, subtraction, and concatenation

PL/SQL evaluates operators of equal precedence in no particular order. When parentheses enclose an expression that is part of a larger expression, PL/SQL evaluates the parenthesized expression first, then uses the result in the larger expression. When parenthesized expressions are nested, PL/SQL evaluates the innermost expression first and the outermost expression last.

Examples

Several examples of expressions follow:

(a + b) > c -- Boolean expression

NOT finished -- Boolean expression

TO_CHAR(acct_no) -- character expression

'Fat ' || 'cats' -- character expression

'15-NOV-05' -- date expression

MONTHS_BETWEEN(d1, d2) -- date expression pi * r**2 -- numeric expression emp_cv%ROWCOUNT -- numeric expression

Related Topics

"Assignment Statement" on page 13-3

"Constant and Variable Declaration" on page 13-25

"EXIT Statement" on page 13-44

"IF Statement" on page 13-64

information, see "Querying Data with PL/SQL" on page 6-14.

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FETCH Statement

The

FETCH

statement retrieves rows of data from the result set of a multi-row query.

You can fetch rows one at a time, several at a time, or all at once. The data is stored in variables or fields that correspond to the columns selected by the query. For more

Syntax

FETCH

fetch statement ::=

cursor_name cursor_variable_name

: host_cursor_variable_name

INTO variable_name record_name

BULK COLLECT INTO collection_name

: host_array_name

, LIMIT numeric_expression

;

Keyword and Parameter Description

BULK COLLECT

Instructs the SQL engine to bulk-bind output collections before returning them to the

PL/SQL engine. The SQL engine bulk-binds all collections referenced in the

INTO

list.

collection_name

A declared collection into which column values are bulk fetched. For each query select_item

, there must be a corresponding, type-compatible collection in the list.

cursor_name

An explicit cursor declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable (or parameter) declared within the current scope.

host_array_name

An array (declared in a PL/SQL host environment and passed to PL/SQL as a bind variable) into which column values are bulk fetched. For each query select_item

, there must be a corresponding, type-compatible array in the list. Host arrays must be prefixed with a colon.

PL/SQL Language Elements

13-53

FETCH Statement

host_cursor_variable_name

LIMIT

This optional clause, allowed only in bulk (not scalar)

FETCH

statements, lets you bulk fetch several rows at a time, rather than the entire result set.

record_name

A user-defined or

%ROWTYPE

record into which rows of values are fetched. For each column value returned by the query associated with the cursor or cursor variable, there must be a corresponding, type-compatible field in the record.

variable_name

A variable into which a column value is fetched. For each column value returned by the query associated with the cursor or cursor variable, there must be a corresponding, type-compatible variable in the list.

Usage Notes

You must use either a cursor

FOR

loop or the

FETCH

statement to process a multi-row query.

Any variables in the

WHERE

clause of the query are evaluated only when the cursor or cursor variable is opened. To change the result set or the values of variables in the query, you must reopen the cursor or cursor variable with the variables set to their new values.

To reopen a cursor, you must close it first. However, you need not close a cursor variable before reopening it.

You can use different

INTO

lists on separate fetches with the same cursor or cursor variable. Each fetch retrieves another row and assigns values to the target variables.

If you

FETCH

past the last row in the result set, the values of the target fields or variables are indeterminate and the

%NOTFOUND

attribute returns

TRUE

PL/SQL makes sure the return type of a cursor variable is compatible with the

INTO clause of the

FETCH

statement. For each column value returned by the query associated with the cursor variable, there must be a corresponding, type-compatible field or variable in the

INTO

clause. Also, the number of fields or variables must equal the number of column values.

When you declare a cursor variable as the formal parameter of a subprogram that fetches from the cursor variable, you must specify the

IN OUT

mode. However, if the subprogram also opens the cursor variable, you must specify the

IN OUT

mode.

Because a sequence of

FETCH

statements always runs out of data to retrieve, no exception is raised when a

FETCH

returns no data. To detect this condition, you must use the cursor attribute

%FOUND

%NOTFOUND

PL/SQL raises the predefined exception

INVALID_CURSOR

if you try to fetch from a closed or never-opened cursor or cursor variable.

Restrictions on BULK COLLECT

The following restrictions apply to the

BULK COLLECT

clause:

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FETCH Statement

■

You cannot bulk collect into an associative array that has a string type for the key.

You can use the

BULK COLLECT

clause only in server-side programs (not in client-side programs). Otherwise, you get the error this feature is not supported in client-side programs

All target variables listed in a

BULK COLLECT INTO

clause must be collections.

Composite targets (such as objects) cannot be used in the

RETURNING INTO clause. Otherwise, you get the error unsupported feature with

RETURNING clause

When implicit datatype conversions are needed, multiple composite targets cannot be used in the

BULK COLLECT INTO

clause.

When an implicit datatype conversion is needed, a collection of a composite target

(such as a collection of objects) cannot be used in the

BULK COLLECT INTO

clause.

Examples

For examples, see the following:

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 6–23, "Passing Parameters to Explicit Cursors" on page 6-19

Example 6–27, "Passing a REF CURSOR as a Parameter" on page 6-22

Example 6–32, "Fetching from a Cursor Variable into a Record" on page 6-25

Example 6–33, "Fetching from a Cursor Variable into Collections" on page 6-25

Example 6–35, "Using a Cursor Expression" on page 6-29

Example 6–41, "Using CURRENT OF to Update the Latest Row Fetched From a

Cursor" on page 6-35

Example 7–4, "Dynamic SQL with BULK COLLECT INTO Clause" on page 7-6

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

"CLOSE Statement" on page 13-16,

"RETURNING INTO Clause" on page 13-101

PL/SQL Language Elements

13-55

FORALL Statement

The

FORALL

statement issues a series of static or dynamic DML statements, usually much faster than an equivalent

FOR

loop. It requires some setup code, because each iteration of the loop must use values from one or more collections in its

VALUES

WHERE

clauses. For more information, see

Statements and Queries with Bulk SQL" on page 11-8.

Syntax

for all statement ::=

SAVE EXCEPTIONS

FORALL index_name IN bounds_clause sql_statement ;

bounds_clause ::=

lower_bound ..

upper_bound

INDICES OF collection

VALUES OF index_collection

BETWEEN lower_bound AND upper_bound

Keyword and Parameter Description

INDICES OF collection_name

A clause specifying that the values of the index variable correspond to the subscripts of the elements of the specified collection. With this clause, you can use

FORALL

with nested tables where some elements have been deleted, or with associative arrays that have numeric subscripts.

BETWEEN lower_bound AND upper_bound

Limits the range of subscripts in the

INDICES OF

clause. If a subscript in the range does not exist in the collection, that subscript is skipped.

VALUES OF index_collection_name

A clause specifying that the subscripts for the

FORALL

index variable are taken from the values of the elements in another collection, specified by index_collection_name

. This other collection acts as a set of pointers;

FORALL

can iterate through subscripts in arbitrary order, even using the same subscript more than once, depending on what elements you include in index_collection_name

The index collection must be a nested table, or an associative array indexed by

PLS_INTEGER

BINARY_INTEGER

, whose elements are also

PLS_INTEGER

BINARY_INTEGER

. If the index collection is empty, an exception is raised and the

FORALL

statement is not executed.

index_name

An undeclared identifier that can be referenced only within the

FORALL

statement and only as a collection subscript.

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FORALL Statement

Usage Notes

Although the SQL statement can reference more than one collection, the performance benefits apply only to subscripted collections.

If a

FORALL

statement fails, database changes are rolled back to an implicit savepoint marked before each execution of the SQL statement. Changes made during previous iterations of the

FORALL

loop are not rolled back.

Restrictions

The implicit declaration of index_name

overrides any other declaration outside the loop. You cannot refer to another variable with the same name inside the statement.

Inside a

FORALL

statement, index_name

cannot appear in expressions and cannot be assigned a value.

lower_bound .. upper_bound

Numeric expressions that specify a valid range of consecutive index numbers. PL/SQL rounds them to the nearest integer, if necessary. The SQL engine executes the SQL statement once for each index number in the range. The expressions are evaluated once, when the

FORALL

statement is entered.

SAVE EXCEPTIONS

Optional keywords that cause the

FORALL

loop to continue even if some DML operations fail. Instead of raising an exception immediately, the program raises a single exception after the

FORALL

statement finishes. The details of the errors are available after the loop in

SQL%BULK_EXCEPTIONS

. The program can report or clean up all the errors after the

FORALL

loop, rather than handling each exception as it happens. See

"Handling FORALL Exceptions with the %BULK_EXCEPTIONS

Attribute" on page 11-14.

sql_statement

A static, such as

UPDATE

DELETE

, or dynamic (

EXECUTE IMMEDIATE

) DML statement that references collection elements in the

VALUES

WHERE

clauses.

The following restrictions apply to the

FORALL

statement:

■

You cannot loop through the elements of an associative array that has a string type for the key.

■

Within a

FORALL

loop, you cannot refer to the same collection in both the

SET clause and the

WHERE

clause of an

UPDATE

statement. You might need to make a second copy of the collection and refer to the new name in the

WHERE

clause.

You can use the

FORALL

statement only in server-side programs, not in client-side programs.

■

The

INSERT

UPDATE

, or

DELETE

statement must reference at least one collection.

For example, a

FORALL

statement that inserts a set of constant values in a loop raises an exception.

When you specify an explicit range, all collection elements in that range must exist. If an element is missing or was deleted, you get an error.

When you use the

INDICES OF

VALUES OF

clauses, all the collections referenced in the DML statement must have subscripts matching the values of the index variable. Make sure that any

DELETE

EXTEND

, and so on operations are applied to all the collections so that they have the same set of subscripts. If any of

PL/SQL Language Elements

13-57

FORALL Statement

■

■ the collections is missing a referenced element, you get an error. If you use the

SAVE EXCEPTIONS

clause, this error is treated like any other error and does not stop the

FORALL

statement.

You cannot refer to individual record fields within DML statements called by a

FORALL

statement. Instead, you can specify the entire record with the

SET ROW clause in an

UPDATE

statement, or the

VALUES

clause in an

INSERT

statement.

Collection subscripts must be just the index variable rather than an expression, such as i

rather than i+1

The cursor attribute

%BULK_ROWCOUNT

cannot be assigned to other collections, or be passed as a parameter to subprograms.

Examples

For examples, see the following:

Example 11–2, "Issuing DELETE Statements in a Loop" on page 11-9

Example 11–3, "Issuing INSERT Statements in a Loop" on page 11-9

Example 11–4, "Using FORALL with Part of a Collection" on page 11-10

Example 11–5, "Using FORALL with Non-Consecutive Index Values" on page 11-10

Example 11–9, "Bulk Operation That Continues Despite Exceptions" on page 11-15

Example 11–16, "Using FORALL With BULK COLLECT" on page 11-19

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Function Declaration

A function is a subprogram that can take parameters and return a single value. A function has two parts: the specification and the body. The specification (spec for short) begins with the keyword

FUNCTION

and ends with the

RETURN

clause, which specifies the datatype of the return value. Parameter declarations are optional.

Functions that take no parameters are written without parentheses. The function body begins with the keyword

(or

) and ends with the keyword

END

followed by an optional function name.

The function body has three parts: an optional declarative part, an executable part, and an optional exception-handling part. The declarative part contains declarations of types, cursors, constants, variables, exceptions, and subprograms. These items are local and cease to exist when you exit the function. The executable part contains statements that assign values, control execution, and manipulate data. The exception-handling part contains handlers that deal with exceptions raised during execution. For more

information, see "Understanding PL/SQL Functions" on page 8-4. For an example of a

function declaration, see Example 9–3 on page 9-6.

Note that the function declaration in a PL/SQL block or package is not the same as creating a function in SQL. For information on the

CREATE FUNCTION

SQL statement, see Oracle Database SQL Reference.

Syntax

function specification ::=

( parameter_declaration )

FUNCTION function_name

RETURN datatype

function declaration ::=

DETERMINISTIC

PARALLEL_ENABLE PIPELINED

;

( parameter_declaration

FUNCTION function_name

PIPELINED

RETURN datatype

)

PL/SQL Language Elements

13-59

Function Declaration

function body ::=

PRAGMA AUTONOMOUS_TRANSACTION ; type_definition item_body

EXCEPTION exception_handler function_body procedure_body

END

BEGIN statement function_name

;

parameter declaration ::=

OUT

IN OUT parameter_name

DEFAULT expression

NOCOPY datatype

Keyword and Parameter Description

datatype

A type specifier. For the syntax of datatype

, see

"Constant and Variable Declaration" on page 13-25.

DETERMINISTIC

A hint that helps the optimizer avoid redundant function calls. If a stored function was called previously with the same arguments, the optimizer can elect to use the previous result. The function result should not depend on the state of session variables or schema objects. Otherwise, results might vary across calls. Only

DETERMINISTIC functions can be called from a function-based index or a materialized view that has query-rewrite enabled. For more information and possible limitations of the

DETERMINISTIC

option, see the

CREATE FUNCTION

statement in the Oracle Database

SQL Reference. See also the

CREATE INDEX

statement in Oracle Database SQL Reference.

exception_handler

Associates an exception with a sequence of statements, which is executed when that exception is raised. For the syntax of exception_handler

, see

Declares a program object. For its syntax, see "Block Declaration" on page 13-8.

expression

An arbitrarily complex combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the declaration is elaborated, the value of expression

is assigned to the parameter. The value and the parameter must have compatible datatypes.

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Function Declaration

function_name

Specifies the name you choose for the function.

IN, OUT, IN OUT

Parameter modes that define the behavior of formal parameters. An

parameter passes values to the subprogram being called. An

OUT

parameter returns values to the caller of the subprogram. An

IN OUT

parameter passes initial values to the subprogram being called, and returns updated values to the caller.

item_declaration

NOCOPY

A compiler hint (not directive) that allows the PL/SQL compiler to pass

OUT

and

OUT

parameters by reference instead of by value (the default). The function can run faster, because it does not have to make temporary copies of these parameters, but the results can be different if the function ends with an unhandled exception. For more

information, see "Using Default Values for Subprogram Parameters" on page 8-9.

PARALLEL_ENABLE

Declares that a stored function can be used safely in the slave sessions of parallel DML evaluations. The state of a main (logon) session is never shared with slave sessions.

Each slave session has its own state, which is initialized when the session begins. The function result should not depend on the state of session ( static

) variables.

Otherwise, results might vary across sessions. For information on the

PARALLEL_ENABLE

option, see the

CREATE FUNCTION

statement in the Oracle

Database SQL Reference.

parameter_name

A formal parameter, a variable declared in a function spec and referenced in the function body.

PIPELINED

specifies to return the results of a table function iteratively. A table function returns a collection type (a nested table or varray) with elements that are SQL datatypes. You can query table functions using the

TABLE

keyword before the function name in the

FROM

clause of a SQL query. For more information, see "Setting Up

Transformations with Pipelined Functions" on page 11-31.

PRAGMA AUTONOMOUS_TRANSACTION

Marks a function as autonomous. An autonomous transaction is an independent transaction started by the main transaction. Autonomous transactions let you suspend the main transaction, do SQL operations, commit or roll back those operations, then resume the main transaction. For more information, see

"Doing Independent Units of

Work with Autonomous Transactions" on page 6-37.

procedure_declaration

Declares a procedure. For the syntax of procedure_declaration

, see

"Procedure

Declaration" on page 13-90.

PL/SQL Language Elements

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Function Declaration

RETURN

Introduces the

RETURN

clause, which specifies the datatype of the return value.

type_definition

Specifies a user-defined datatype. For its syntax

, see

"Block Declaration" on page 13-8.

:= | DEFAULT

Initializes

parameters to default values.

Usage Notes

A function is called as part of an expression: promotable := sal_ok(new_sal, new_title) AND (rating > 3);

To be callable from SQL statements, a stored function must obey certain rules that

control side effects. See "Controlling Side Effects of PL/SQL Subprograms" on page 8-23.

In a function, at least one execution path must lead to a

RETURN

statement. Otherwise, you get a function returned without value

error at run time. The

RETURN statement must contain an expression, which is evaluated when the

RETURN

statement is executed. The resulting value is assigned to the function identifier, which acts like a variable.

You can write the function spec and body as a unit. Or, you can separate the function spec from its body. That way, you can hide implementation details by placing the function in a package. You can define functions in a package body without declaring their specs in the package spec. However, such functions can be called only from inside the package.

Inside a function, an

parameter acts like a constant; you cannot assign it a value.

OUT

parameter acts like a local variable; you can change its value and reference the value in any way. An

IN OUT

parameter acts like an initialized variable; you can assign it a value, which can be assigned to another variable. For information about the parameter modes, see

Table 8–1 on page 8-9.

Avoid using the

OUT

and

IN OUT

modes with functions. The purpose of a function is to take zero or more parameters and return a single value. Functions should be free from side effects, which change the values of variables not local to the subprogram.

Examples

For examples, see the following:

Example 1–13, "Creating a Package and Package Body" on page 1-14

Example 2–15, "Using a Subprogram Name for Name Resolution" on page 2-15

Example 2–27, "Using a Search Condition With a CASE Statement" on page 2-27

Example 5–44, "Returning a Record from a Function" on page 5-31

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Example 6–48, "Calling an Autonomous Function" on page 6-42

Example 9–3, "Creating the emp_admin Package" on page 9-6

Related Topics

"Using the GOTO Statement" on page 4-13.

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GOTO Statement

The

GOTO

statement branches unconditionally to a statement label or block label. The label must be unique within its scope and must precede an executable statement or a

PL/SQL block. The

GOTO

statement transfers control to the labelled statement or block.

For more information, see

Syntax

label declaration ::=

<< label_name >>

goto statement ::=

GOTO label_name ;

Keyword and Parameter Description

label_name

A label that you assigned to an executable statement or a PL/SQL block. A

GOTO statement transfers control to the statement or block following

<<label_name>>

Usage Notes

GOTO

label must precede an executable statement or a PL/SQL block. A

GOTO statement cannot branch into an

statement,

LOOP

statement, or sub-block. To branch to a place that does not have an executable statement, add the

NULL

statement.

From the current block, a

GOTO

statement can branch to another place in the block or into an enclosing block, but not into an exception handler. From an exception handler, a

GOTO

statement can branch into an enclosing block, but not into the current block.

If you use the

GOTO

statement to exit a cursor

FOR

loop prematurely, the cursor is closed automatically. The cursor is also closed automatically if an exception is raised inside the loop.

A given label can appear only once in a block. However, the label can appear in other blocks including enclosing blocks and sub-blocks. If a

GOTO

statement cannot find its target label in the current block, it branches to the first enclosing block in which the label appears.

Examples

For examples, see the following:

Example 4–19, "Using a Simple GOTO Statement" on page 4-14

Example 4–21, "Using a GOTO Statement to Branch an Enclosing Block" on page 4-14

PL/SQL Language Elements

13-63

IF Statement

The

statement executes or skips a sequence of statements, depending on the value of a Boolean expression. For more information, see

"Testing Conditions: IF and CASE

Statements" on page 4-2.

Syntax

if statement ::=

IF boolean_expression THEN statement

ELSIF boolean_expression THEN statement

ELSE statement

END IF ;

Keyword and Parameter Description

boolean_expression

An expression that returns the Boolean value

TRUE

FALSE

, or

NULL

. Examples are comparisons for equality, greater-than, or less-than. The sequence following the THEN keyword is executed only if the expression returns

TRUE

ELSE

If control reaches this keyword, the sequence of statements that follows it is executed.

This occurs when none of the previous conditional tests returned

TRUE

ELSIF

Introduces a Boolean expression that is evaluated if none of the preceding conditions returned

TRUE

THEN

If the expression returns

TRUE

, the statements after the THEN keyword are executed.

Usage Notes

There are three forms of

statements:

IF-THEN

IF-THEN-ELSE

, and

IF-THEN-ELSIF

. The simplest form of

statement associates a Boolean expression with a sequence of statements enclosed by the keywords

THEN

and

END IF

. The sequence of statements is executed only if the expression returns

TRUE

. If the expression returns

FALSE

NULL

, the

statement does nothing. In either case, control passes to the next statement.

The second form of

statement adds the keyword

ELSE

followed by an alternative sequence of statements. The sequence of statements in the

ELSE

clause is executed only if the Boolean expression returns

FALSE

NULL

. Thus, the

ELSE

clause ensures that a sequence of statements is executed.

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IF Statement

The third form of

statement uses the keyword

ELSIF

to introduce additional

Boolean expressions. If the first expression returns

FALSE

NULL

, the

ELSIF

clause evaluates another expression. An

statement can have any number of

ELSIF clauses; the final

ELSE

clause is optional. Boolean expressions are evaluated one by one from top to bottom. If any expression returns

TRUE

, its associated sequence of statements is executed and control passes to the next statement. If all expressions return

FALSE

NULL

, the sequence in the

ELSE

clause is executed.

statement never executes more than one sequence of statements because processing is complete after any sequence of statements is executed. However, the

THEN

and

ELSE

clauses can include more

statements. That is,

statements can be nested.

Examples

Example 13–3 shows an example of the

IF-THEN-ELSIF-ELSE

statement.

Example 13–3 Using the IF Statement

DECLARE

jobid employees.job_id%TYPE;

empid employees.employee_id%TYPE := 115;

sal_raise NUMBER(3,2);

BEGIN

SELECT job_id INTO jobid from employees WHERE employee_id = empid;

IF jobid = 'PU_CLERK' THEN sal_raise := .09;

ELSIF jobid = 'SH_CLERK' THEN sal_raise := .08;

ELSIF jobid = 'ST_CLERK' THEN sal_raise := .07;

ELSE sal_raise := 0;

END IF;

END;

For examples, see the following:

Example 1–7, "Using the IF-THEN_ELSE and CASE Statement for Conditional

Control" on page 1-10

Example 4–1, "Using a Simple IF-THEN Statement" on page 4-2

Example 4–2, "Using a Simple IF-THEN-ELSE Statement" on page 4-2

Example 4–3, "Nested IF Statements" on page 4-3

Example 4–4, "Using the IF-THEN-ELSEIF Statement" on page 4-3

"CASE Statement" on page 13-14

"RETURNING INTO Clause" on page 13-101.

PL/SQL Language Elements

13-65

INSERT Statement

The

INSERT

statement adds one or more new rows of data to a database table. For a full description of the

INSERT

statement, see Oracle Database SQL Reference.

Syntax

insert statement ::=

INSERT INTO ( table_reference subquery

TABLE (

) subquery2 ) alias

( column_name )

, returning_clause

VALUES ( subquery3 sql_expression )

;

Keyword and Parameter Description

alias

Another (usually short) name for the referenced table or view.

column_name[, column_name]...

A list of columns in a database table or view. The columns can be listed in any order, as long as the expressions in the

VALUES

clause are listed in the same order. Each column name can only be listed once. If the list does not include all the columns in a table, each missing columns is set to

NULL

or to a default value specified in the

CREATE

TABLE

statement.

returning_clause

Returns values from inserted rows, eliminating the need to

SELECT

the rows afterward. You can retrieve the column values into variables or into collections. You cannot use the

RETURNING

clause for remote or parallel inserts. If the statement does not affect any rows, the values of the variables specified in the

RETURNING

clause are undefined. For the syntax of returning_clause

, see

sql_expression

Any expression valid in SQL. For example, it could be a literal, a PL/SQL variable, or a

SQL query that returns a single value. For more information, see Oracle Database SQL

Reference. PL/SQL also lets you use a record variable here.

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INSERT Statement

subquery

SELECT

statement that provides a set of rows for processing. Its syntax is like that of select_into_statement

without the

INTO

clause. See

see "DELETE Statement" on page 13-36.

subquery3

SELECT

statement that returns a set of rows. Each row returned by the select statement is inserted into the table. The subquery must return a value for every column in the column list, or for every column in the table if there is no column list.

table_reference

A table or view that must be accessible when you execute the

INSERT

statement, and for which you must have

INSERT

privileges. For the syntax of table_reference

TABLE (subquery2)

The operand of

TABLE

is a

SELECT

statement that returns a single column value representing a nested table. This operator specifies that the value is a collection, not a scalar value.

VALUES (...)

Assigns the values of expressions to corresponding columns in the column list. If there is no column list, the first value is inserted into the first column defined by the

CREATE

TABLE

statement, the second value is inserted into the second column, and so on.

There must be one value for each column in the column list. The datatypes of the values being inserted must be compatible with the datatypes of corresponding columns in the column list.

Usage Notes

Character and date literals in the

VALUES

list must be enclosed by single quotes (').

Numeric literals are not enclosed by quotes.

The implicit cursor

SQL

and the cursor attributes

%NOTFOUND

%FOUND

%ROWCOUNT

, and

%ISOPEN

let you access useful information about the execution of an

INSERT statement.

Examples

For examples, see the following:

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

Example 6–5, "Using CURRVAL and NEXTVAL" on page 6-4

Example 6–38, "Using SAVEPOINT With ROLLBACK" on page 6-31

Example 6–46, "Declaring an Autonomous Trigger" on page 6-38

Example 6–48, "Calling an Autonomous Function" on page 6-42

Example 9–3, "Creating the emp_admin Package" on page 9-6

Related Topics

"DELETE Statement" on page 13-36

"UPDATE Statement" on page 13-121

PL/SQL Language Elements

13-67

Literal Declaration

A literal is an explicit numeric, character, string, or Boolean value not represented by an identifier. The numeric literal 135 and the string literal

'hello world'

are examples. For more information, see

"Literals" on page 2-4.

Syntax

numeric literal ::=

– integer real_number

integer literal ::=

digit

real number literal ::=

– integer

integer

character literal ::=

character ’

’’

’

string literal ::=

character

’’

’ ’

E e integer

boolean literal ::=

TRUE

FALSE

NULL

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Literal Declaration

Keyword and Parameter Description

character

A member of the PL/SQL character set. For more information, see "Character Sets and

Lexical Units" on page 2-1.

digit

One of the numerals 0 .. 9.

TRUE, FALSE, NULL

A predefined Boolean value.

Usage Notes

Integer and real numeric literals can be used in arithmetic expressions. Numeric literals must be separated by punctuation. Spaces can be used in addition to the

punctuation. For additional information, see "Numeric Literals" on page 2-5.

A character literal is an individual character enclosed by single quotes (apostrophes).

Character literals include all the printable characters in the PL/SQL character set: letters, numerals, spaces, and special symbols. PL/SQL is case sensitive within character literals. For example, PL/SQL considers the literals

'Q'

and

'q'

to be

different. For additional information, see "Character Literals" on page 2-6.

A string literal is a sequence of zero or more characters enclosed by single quotes. The null string (

) contains zero characters. A string literal can hold up to 32,767 characters. PL/SQL is case sensitive within string literals. For example, PL/SQL considers the literals

'white'

and

'White'

to be different.

To represent an apostrophe within a string, enter two single quotes instead of one. For literals where doubling the quotes is inconvenient or hard to read, you can designate an escape character using the notation q'

esc_char

...

esc_char

. This escape character must not occur anywhere else inside the string.

Trailing blanks are significant within string literals, so

'abc'

and

'abc '

are different. Trailing blanks in a string literal are not trimmed during PL/SQL processing, although they are trimmed if you insert that value into a table column of type

CHAR

For additional information, including

NCHAR

string literals, see "String Literals" on page 2-6.

The

BOOLEAN

values

TRUE

and

FALSE

cannot be inserted into a database column. For additional information, see

"BOOLEAN Literals" on page 2-7.

Examples

Several examples of numeric literals are:

25 6.34 7E2 25e-03 .1 1. +17 -4.4 -4.5D -4.6F

Several examples of character literals are:

'H' '&' ' ' '9' ']' 'g'

Several examples of string literals are:

'$5,000'

'02-AUG-87'

'Don''t leave until you''re ready and I''m ready.' q'#Don't leave until you're ready and I'm ready.#'

PL/SQL Language Elements

13-69

Literal Declaration

For examples, see the following:

Example 2–3, "Using DateTime Literals" on page 2-7

Example 2–34, "Using Conditional Compilation With Database Versions" on page 2-35

"Using LOCK TABLE" on page 6-35.

"Literals" on page 2-4

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LOCK TABLE Statement

The

LOCK TABLE

statement locks entire database tables in a specified lock mode. That enables you to share or deny access to tables while maintaining their integrity. For more information, see

Oracle has extensive automatic features that allow multiple programs to read and write data simultaneously, while each program sees a consistent view of the data; you should rarely, if ever, need to lock tables yourself. For additional information on the

LOCK TABLE

SQL statement, see Oracle Database SQL Reference.

Syntax

lock table statement ::=

NOWAIT

LOCK TABLE table_reference IN lock_mode MODE ;

Keyword and Parameter Description

table_reference

A table or view that must be accessible when you execute the

LOCK TABLE

statement.

For the syntax of table_reference

, see

"DELETE Statement" on page 13-36.

lock_mode

The type of lock. It must be one of the following:

ROW SHARE

ROW EXCLUSIVE

UPDATE

SHARE ROW EXCLUSIVE

, or

EXCLUSIVE

NOWAIT

This optional keyword tells Oracle not to wait if the table has been locked by another user. Control is immediately returned to your program, so it can do other work before trying again to acquire the lock.

Usage Notes

If you omit the keyword

NOWAIT

, Oracle waits until the table is available; the wait has no set limit. Table locks are released when your transaction issues a commit or rollback. A table lock never keeps other users from querying a table, and a query never acquires a table lock. If your program includes SQL locking statements, make sure the

Oracle users requesting locks have the privileges needed to obtain the locks. Your DBA can lock any table. Other users can lock tables they own or tables for which they have a privilege, such as

SELECT

INSERT

UPDATE

, or

DELETE

Examples

This statement locks the employees

table in row shared mode with the

NOWAIT option:

LOCK TABLE employees IN ROW SHARE MODE NOWAIT;

Related Topics

information, see "Controlling Loop Iterations: LOOP and EXIT Statements" on page 4-7.

PL/SQL Language Elements

13-71

LOOP Statements

LOOP

statements execute a sequence of statements multiple times. The LOOP and

END LOOP keywords enclose the statements. PL/SQL provides four kinds of loop statements: basic loop,

WHILE

loop,

FOR

loop, and cursor

FOR

loop. For usage

Syntax

loop statement ::=

<< label_name >> label_name

LOOP statement END LOOP ;

while loop statement ::=

<< label_name >>

WHILE boolean_expression label_name

LOOP statement

for loop statement ::=

<< label_name >>

END LOOP

FOR index_name IN

;

REVERSE

LOOP lower_bound ..

upper_bound label_name statement END LOOP ;

cursor for loop statement ::=

<< label_name >>

FOR record_name IN

( cursor_name select_statement

( cursor_parameter_name

) label_name

LOOP statement END LOOP

)

;

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LOOP Statements

Keyword and Parameter Description

basic_loop_statement

A loop that executes an unlimited number of times. It encloses a sequence of statements between the keywords

LOOP

and

END LOOP

. With each iteration, the sequence of statements is executed, then control resumes at the top of the loop. An

EXIT

GOTO

, or

RAISE

statement branches out of the loop. A raised exception also ends the loop.

boolean_expression

An expression that returns the Boolean value

TRUE

FALSE

, or

NULL

. It is associated with a sequence of statements, which is executed only if the expression returns

TRUE

For the syntax of boolean_expression

, see

"Expression Definition" on page 13-45.

cursor_for_loop_statement

Issues a SQL query and loops through the rows in the result set. This is a convenient technique that makes processing a query as simple as reading lines of text in other programming languages.

A cursor

FOR

loop implicitly declares its loop index as a

%ROWTYPE

record, opens a cursor, repeatedly fetches rows of values from the result set into fields in the record, and closes the cursor when all rows have been processed.

cursor_name

An explicit cursor previously declared within the current scope. When the cursor

FOR loop is entered, cursor_name

cannot refer to a cursor already opened by an

OPEN statement or an enclosing cursor

FOR

loop.

cursor_parameter_name

A variable declared as the formal parameter of a cursor. For the syntax of cursor_parameter_declaration

, see

"Cursor Declaration" on page 13-33. A

cursor parameter can appear in a query wherever a constant can appear. The formal parameters of a cursor must be

parameters.

for_loop_statement

Numeric

FOR_LOOP

loops iterate over a specified range of integers. The range is part of an iteration scheme, which is enclosed by the keywords

FOR

and

LOOP

The range is evaluated when the

FOR

loop is first entered and is never re-evaluated.

The loop body is executed once for each integer in the range defined by lower_bound..upper_bound

. After each iteration, the loop index is incremented.

index_name

An undeclared identifier that names the loop index (sometimes called a loop counter).

Its scope is the loop itself; you cannot reference the index outside the loop.

The implicit declaration of index_name

overrides any other declaration outside the loop. To refer to another variable with the same name, use a label. See

Example 4–15,

"Using a Label for Referencing Variables Outside a Loop" on page 4-12.

Inside a loop, the index is treated like a constant: it can appear in expressions, but cannot be assigned a value.

PL/SQL Language Elements

13-73

LOOP Statements

label_name

An optional undeclared identifier that labels a loop. label_name

must be enclosed by double angle brackets and must appear at the beginning of the loop. Optionally, label_name

(not enclosed in angle brackets) can also appear at the end of the loop.

You can use label_name

in an

EXIT

statement to exit the loop labelled by label_name

. You can exit not only the current loop, but any enclosing loop.

You cannot reference the index of a

FOR

loop from a nested

FOR

loop if both indexes have the same name, unless the outer loop is labeled by label_name

and you use dot notation. See

Example 4–16, "Using Labels on Loops for Referencing" on page 4-12.

lower_bound .. upper_bound

Expressions that return numbers. Otherwise, PL/SQL raises the predefined exception

VALUE_ERROR

. The expressions are evaluated only when the loop is first entered. The lower bound need not be 1, it can be a negative integer as in

FOR i IN -5..10

. The loop counter increment (or decrement) must be 1.

Internally, PL/SQL assigns the values of the bounds to temporary

PLS_INTEGER variables, and, if necessary, rounds the values to the nearest integer. The magnitude range of a

PLS_INTEGER

is -2147483648 to 2147483647, represented in 32 bits. If a bound evaluates to a number outside that range, you get a numeric overflow error when

PL/SQL attempts the assignment. See "PLS_INTEGER Datatype" on page 3-4.

By default, the loop index is assigned the value of lower_bound

. If that value is not greater than the value of upper_bound

, the sequence of statements in the loop is executed, then the index is incremented. If the value of the index is still not greater than the value of upper_bound

, the sequence of statements is executed again. This process repeats until the value of the index is greater than the value of upper_bound

At that point, the loop completes.

record_name

An implicitly declared record. The record has the same structure as a row retrieved by cursor_name

or select_statement

The record is defined only inside the loop. You cannot refer to its fields outside the loop. The implicit declaration of record_name

overrides any other declaration outside the loop. You cannot refer to another record with the same name inside the loop unless you qualify the reference using a block label.

Fields in the record store column values from the implicitly fetched row. The fields have the same names and datatypes as their corresponding columns. To access field values, you use dot notation, as follows: record_name.field_name

Select-items fetched from the

FOR

loop cursor must have simple names or, if they are expressions, must have aliases. In the following example, wages

is an alias for the select item salary+NVL(commission_pct,0)*1000

CURSOR c1 IS SELECT employee_id,

salary + NVL(commission_pct,0) * 1000 wages FROM employees ...

REVERSE

By default, iteration proceeds upward from the lower bound to the upper bound. If you use the keyword

REVERSE

, iteration proceeds downward from the upper bound to the lower bound. An example follows:

BEGIN

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LOOP Statements

FOR i IN REVERSE 1..10 LOOP -- i starts at 10, ends at 1

DBMS_OUTPUT.PUT_LINE(i); -- statements here execute 10 times

END LOOP;

END;

The loop index is assigned the value of upper_bound

. If that value is not less than the value of lower_bound

, the sequence of statements in the loop is executed, then the index is decremented. If the value of the index is still not less than the value of lower_bound

, the sequence of statements is executed again. This process repeats until the value of the index is less than the value of lower_bound

. At that point, the loop completes.

select_statement

A query associated with an internal cursor unavailable to you. Its syntax is like that of select_into_statement

without the

INTO

clause. See

"SELECT INTO Statement" on page 13-107. PL/SQL automatically declares, opens, fetches from, and closes the

internal cursor. Because select_statement

is not an independent statement, the implicit cursor

SQL

does not apply to it.

while_loop_statement

The

WHILE-LOOP

statement associates a Boolean expression with a sequence of statements enclosed by the keywords

LOOP

and

END LOOP

. Before each iteration of the loop, the expression is evaluated. If the expression returns

TRUE

, the sequence of statements is executed, then control resumes at the top of the loop. If the expression returns

FALSE

NULL

, the loop is bypassed and control passes to the next statement.

Usage Notes

You can use the

EXIT WHEN

statement to exit any loop prematurely. If the Boolean expression in the

WHEN

clause returns

TRUE

, the loop is exited immediately.

When you exit a cursor

FOR

loop, the cursor is closed automatically even if you use an

EXIT

GOTO

statement to exit the loop prematurely. The cursor is also closed automatically if an exception is raised inside the loop.

Examples

For examples, see the following:

Example 4–18, "Using EXIT With a Label in a LOOP" on page 4-13

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

"EXIT Statement" on page 13-44

Example 1–12, "Creating a Stored Subprogram" on page 1-13

PL/SQL Language Elements

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MERGE Statement

The

MERGE

statement inserts some rows and updates others in a single operation. The decision about whether to update or insert into the target table is based upon a join condition: rows already in the target table that match the join condition are updated; otherwise, a row is inserted using values from a separate subquery.

For a full description and examples of the

MERGE

statement, see Oracle Database SQL

Reference.

Usage Notes

This statement is primarily useful in data warehousing situations where large amounts of data are commonly inserted and updated. If you only need to insert or update a single row, it is more efficient to do that with the regular PL/SQL techniques: try to update the row, and do an insert instead if the update affects zero rows; or try to insert the row, and do an update instead if the insert raises an exception because the table already contains that primary key.

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NULL Statement

The

NULL

statement is a no-op (no operation); it passes control to the next statement without doing anything. In the body of an

IF-THEN

clause, a loop, or a procedure, the

NULL

statement serves as a placeholder. For more information, see

"Using the NULL

Statement" on page 4-15.

Syntax

null statement ::=

NULL ;

Usage Notes

The

NULL

statement improves readability by making the meaning and action of conditional statements clear. It tells readers that the associated alternative has not been overlooked: you have decided that no action is necessary.

Certain clauses in PL/SQL, such as in an

statement or an exception handler, must contain at least one executable statement. You can use the

NULL

statement to make these constructs compile, while not taking any action.

You might not be able to branch to certain places with the

GOTO

statement because the next statement is

END

END IF

, and so on, which are not executable statements. In these cases, you can put a

NULL

statement where you want to branch.

The

NULL

statement and Boolean value

NULL

are not related.

Examples

For examples, see the following:

Example 1–16, "Declaring a Record Type" on page 1-17

Example 4–20, "Using a NULL Statement to Allow a GOTO to a Label" on page 4-14

Example 4–22, "Using the NULL Statement to Show No Action" on page 4-15

Example 4–23, "Using NULL as a Placeholder When Creating a Subprogram" on page 4-16

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Object Type Declaration

An object type is a user-defined composite datatype that encapsulates a data structure along with the functions and procedures needed to manipulate the data. The variables that form the data structure are called attributes. The functions and procedures that characterize the behavior of the object type are called methods. A special kind of method called the constructor creates a new instance of the object type and fills in its attributes.

Object types must be created through SQL and stored in an Oracle database, where they can be shared by many programs. When you define an object type using the

CREATE TYPE

statement, you create an abstract template for some real-world object.

The template specifies the attributes and behaviors the object needs in the application environment. For information on the

CREATE TYPE

SQL statement, see Oracle Database

SQL Reference. For information on the

CREATE TYPE BODY

SQL statement, see Oracle

Database SQL Reference.

The data structure formed by the set of attributes is public (visible to client programs).

However, well-behaved programs do not manipulate it directly. Instead, they use the set of methods provided, so that the data is kept in a proper state.

For more information on object types, see Oracle Database Application Developer's Guide

- Object-Relational Features. For information on using PL/SQL with object types, see

Chapter 12, "Using PL/SQL With Object Types" .

Usage Notes

Once an object type is created in your schema, you can use it to declare objects in any

PL/SQL block, subprogram, or package. For example, you can use the object type to specify the datatype of an object attribute, table column, PL/SQL variable, bind variable, record field, collection element, formal procedure parameter, or function result.

Like a package, an object type has two parts: a specification and a body. The specification (spec for short) is the interface to your applications; it declares a data structure (set of attributes) along with the operations (methods) needed to manipulate the data. The body fully defines the methods, and so implements the spec.

All the information a client program needs to use the methods is in the spec. Think of the spec as an operational interface and of the body as a black box. You can debug, enhance, or replace the body without changing the spec.

An object type encapsulates data and operations. You can declare attributes and methods in an object type spec, but not constants, exceptions, cursors, or types. At least one attribute is required (the maximum is 1000); methods are optional.

In an object type spec, all attributes must be declared before any methods. Only subprograms have an underlying implementation. If an object type spec declares only attributes and/or call specs, the object type body is unnecessary. You cannot declare attributes in the body. All declarations in the object type spec are public (visible outside the object type).

You can refer to an attribute only by name (not by its position in the object type). To access or change the value of an attribute, you use dot notation. Attribute names can be chained, which lets you access the attributes of a nested object type.

In an object type, methods can reference attributes and other methods without a qualifier. In SQL statements, calls to a parameterless method require an empty

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Object Type Declaration parameter list. In procedural statements, an empty parameter list is optional unless you chain calls, in which case it is required for all but the last call.

From a SQL statement, if you call a

MEMBER

method on a null instance (that is,

SELF

is null), the method is not invoked and a null is returned. From a procedural statement, if you call a

MEMBER

method on a null instance, PL/SQL raises the predefined exception

SELF_IS_NULL

before the method is invoked.

You can declare a map method or an order method but not both. If you declare either method, you can compare objects in SQL and procedural statements. However, if you declare neither method, you can compare objects only in SQL statements and only for equality or inequality. Two objects of the same type are equal only if the values of their corresponding attributes are equal.

Like packaged subprograms, methods of the same kind (functions or procedures) can be overloaded. That is, you can use the same name for different methods if their formal parameters differ in number, order, or datatype family.

Every object type has a default constructor method (constructor for short), which is a system-defined function with the same name as the object type. You use the constructor to initialize and return an instance of that object type. You can also define your own constructor methods that accept different sets of parameters. PL/SQL never calls a constructor implicitly, so you must call it explicitly. Constructor calls are allowed wherever function calls are allowed.

Related Topics

more information, see "Querying Data with PL/SQL" on page 6-14.

PL/SQL Language Elements

13-79

OPEN Statement

The

OPEN

statement executes the query associated with a cursor. It allocates database resources to process the query and identifies the result set -- the rows that match the query conditions. The cursor is positioned before the first row in the result set. For

Syntax

open statement ::=

( cursor_parameter_name )

OPEN cursor_name ;

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope and not currently open.

cursor_parameter_name

A variable declared as the formal parameter of a cursor. (For the syntax of cursor_parameter_declaration

, see

"Cursor Declaration" on page 13-33.) A

cursor parameter can appear in a query wherever a constant can appear.

Usage Notes

Generally, PL/SQL parses an explicit cursor only the first time it is opened and parses a SQL statement (creating an implicit cursor) only the first time the statement is executed. All the parsed SQL statements are cached. A SQL statement is reparsed only if it is aged out of the cache by a new SQL statement. Although you must close a cursor before you can reopen it, PL/SQL need not reparse the associated

SELECT statement. If you close, then immediately reopen the cursor, a reparse is definitely not needed.

Rows in the result set are not retrieved when the

OPEN

statement is executed. The

FETCH

statement retrieves the rows. With a

FOR UPDATE

cursor, the rows are locked when the cursor is opened.

If formal parameters are declared, actual parameters must be passed to the cursor. The formal parameters of a cursor must be

parameters; they cannot return values to actual parameters. The values of actual parameters are used when the cursor is opened. The datatypes of the formal and actual parameters must be compatible. The query can also reference PL/SQL variables declared within its scope.

Unless you want to accept default values, each formal parameter in the cursor declaration must have a corresponding actual parameter in the

OPEN

statement.

Formal parameters declared with a default value do not need a corresponding actual parameter. They assume their default values when the

OPEN

statement is executed.

You can associate the actual parameters in an

OPEN

statement with the formal parameters in a cursor declaration using positional or named notation.

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OPEN Statement

If a cursor is currently open, you cannot use its name in a cursor

FOR

loop.

Examples

For examples, see the following:

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Related Topics

row in the result set. For more information, see "Using Cursor Variables (REF

PL/SQL Language Elements

13-81

OPEN-FOR Statement

The

OPEN-FOR

statement executes the query associated with a cursor variable. It allocates database resources to process the query and identifies the result set -- the rows that meet the query conditions. The cursor variable is positioned before the first

CURSORs)" on page 6-20.

With the optional

USING

clause, the statement associates a cursor variable with a query, executes the query, identifies the result set, positions the cursor before the first row in the result set, then zeroes the rows-processed count kept by

%ROWCOUNT

. For

more information, see "Building a Dynamic Query with Dynamic SQL" on page 7-7.

Because this statement can use bind variables to make the SQL processing more efficient, use the

OPEN-FOR-USING

statement when building a query where you know the

WHERE

clauses in advance. Use the

OPEN-FOR

statement when you need the flexibility to process a dynamic query with an unknown number of

WHERE

clauses.

Syntax

open for statement ::=

OPEN cursor_variable_name

: host_cursor_variable_name

FOR select_statement using_clause

;

using clause ::=

OUT

IN_OUT ,

USING bind_argument

Keyword and Parameter Description

bind_argument

An expression whose value is passed to the dynamic

SELECT

statement.

cursor_variable_name

A cursor variable or parameter (without a return type) previously declared within the current scope.

host_cursor_variable_name

A cursor variable previously declared in a PL/SQL host environment and passed to

PL/SQL as a bind variable. The datatype of the host cursor variable is compatible with the return type of any PL/SQL cursor variable. Host variables must be prefixed with a colon.

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OPEN-FOR Statement

select_statement

A query associated with cursor_variable

, which returns a set of values. The query can reference bind variables and PL/SQL variables, parameters, and functions. The syntax of select_statement

is similar to the syntax for select_into_statement

defined in

"SELECT INTO Statement" on page 13-107,

except that the cursor select_statement

cannot have an

INTO

clause. The length of the dynamic string cannot exceed 32767K.

USING clause

This optional clause specifies a list of bind arguments. At run time, bind arguments in the

USING

clause replace corresponding placeholders in the dynamic

SELECT statement.

Usage Notes

You can declare a cursor variable in a PL/SQL host environment such as an OCI or

Pro*C program. To open the host cursor variable, you can pass it as a bind variable to an anonymous PL/SQL block. You can reduce network traffic by grouping

OPEN-FOR statements. For example, the following PL/SQL block opens five cursor variables in a single round-trip:

/* anonymous PL/SQL block in host environment */

BEGIN

OPEN :emp_cv FOR SELECT * FROM employees;

OPEN :dept_cv FOR SELECT * FROM departments;

OPEN :grade_cv FOR SELECT * FROM salgrade;

OPEN :pay_cv FOR SELECT * FROM payroll;

OPEN :ins_cv FOR SELECT * FROM insurance;

END;

Other

OPEN-FOR

statements can open the same cursor variable for different queries.

You do not need to close a cursor variable before reopening it. When you reopen a cursor variable for a different query, the previous query is lost.

Unlike cursors, cursor variables do not take parameters. Instead, you can pass whole queries (not just parameters) to a cursor variable. Although a PL/SQL stored procedure or function can open a cursor variable and pass it back to a calling subprogram, the calling and called subprograms must be in the same instance. You cannot pass or return cursor variables to procedures and functions called through database links. When you declare a cursor variable as the formal parameter of a subprogram that opens the cursor variable, you must specify the

IN OUT

mode. That way, the subprogram can pass an open cursor back to the caller.

You use three statements to process a dynamic multi-row query:

OPEN-FOR-USING

FETCH

, and

. First, you

OPEN

a cursor variable

FOR

a multi-row query. Then, you

FETCH

rows from the result set. When all the rows are processed, you

the cursor variable.

The dynamic string can contain any multi-row

SELECT

statement (without the terminator). The string can also contain placeholders for bind arguments. However, you cannot use bind arguments to pass the names of schema objects to a dynamic SQL statement.

Every placeholder in the dynamic string must be associated with a bind argument in the

USING

clause. Numeric, character, and string literals are allowed in the

USING clause, but Boolean literals (

TRUE

FALSE

NULL

) are not. To pass nulls to the dynamic

string, you must use a workaround. See "Passing Nulls to Dynamic SQL" on page 7-10.

PL/SQL Language Elements

13-83

OPEN-FOR Statement

Any bind arguments in the query are evaluated only when the cursor variable is opened. To fetch from the cursor using different bind values, you must reopen the cursor variable with the bind arguments set to their new values.

Dynamic SQL supports all the SQL datatypes. For example, bind arguments can be collections,

LOB s, instances of an object type, and refs. As a rule, dynamic SQL does not support PL/SQL-specific types. For instance, bind arguments cannot be

BOOLEAN s or index-by tables.

Examples

For examples, see the following:

Example 6–27, "Passing a REF CURSOR as a Parameter" on page 6-22

Example 6–29, "Stored Procedure to Open a Ref Cursor" on page 6-23

Example 6–30, "Stored Procedure to Open Ref Cursors with Different Queries" on page 6-23

Example 6–31, "Cursor Variable with Different Return Types" on page 6-24

Example 6–32, "Fetching from a Cursor Variable into a Record" on page 6-25

Example 6–33, "Fetching from a Cursor Variable into Collections" on page 6-25

Example 7–9, "Dynamic SQL Fetching into a Record" on page 7-12

Related Topics

"EXECUTE IMMEDIATE Statement" on page 13-41

Chapter 9, "Using PL/SQL Packages" . For an example of a package declaration, see

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Package Declaration

A package is a schema object that groups logically related PL/SQL types, items, and subprograms. Use packages when writing a set of related subprograms that form an application programming interface (API) that you or others might reuse. Packages have two parts: a specification (spec for short) and a body. For more information, see

Example 9–3 on page 9-6.

This section discusses the package specification and body options for PL/SQL. For information on the

CREATE PACKAGE

SQL statement, see Oracle Database SQL

Reference. For information on the

CREATE PACKAGE BODY

SQL statement, see Oracle

Database SQL Reference.

Syntax

package specification ::=

PRAGMA SERIALLY_REUSABLE ; collection_type_definition record_type_definition subtype_definition collection_declaration constant_declaration exception_declaration object_declaration record_declaration variable_declaration cursor_spec function_spec procedure_spec call_spec

PRAGMA RESTRICT_REFERENCES

END package_name

;

PL/SQL Language Elements

13-85

Package Declaration

package body ::=

BEGIN statement

END

package_name

;

Keyword and Parameter Description

call_spec

Publishes a Java method or external C function in the Oracle data dictionary. It publishes the routine by mapping its name, parameter types, and return type to their

SQL counterparts. For more information, see Oracle Database Java Developer's Guide and

Oracle Database Application Developer's Guide - Fundamentals.

collection_declaration

Declares a collection (nested table, index-by table, or varray). For the syntax of collection_declaration

, see

"Collection Definition" on page 13-17.

collection_type_definition

Defines a collection type using the datatype specifier

TABLE

VARRAY

constant_declaration

Declares a constant. For the syntax of constant_declaration

, see

"Constant and

"Cursor Declaration" on page 13-33.

cursor_body

Defines the underlying implementation of an explicit cursor. For the syntax of cursor_body

, see

cursor_spec

Declares the interface to an explicit cursor. For the syntax of cursor_spec

, see

"Cursor Declaration" on page 13-33.

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Package Declaration

exception_declaration

Declares an exception. For the syntax of exception_declaration

, see

"Function Declaration" on page 13-59.

function_body

Implements a function. For the syntax of function_body

, see

function_spec

Declares the interface to a function. For the syntax of function_spec

, see

"Function

Declaration" on page 13-59.

object_declaration

Declares an object (instance of an object type). For the syntax of object_declaration

, see

"Object Type Declaration" on page 13-78.

package_name

A package stored in the database. For naming conventions, see

"Identifiers" on page 2-3.

pragma_restrict_refs

Pragma

RESTRICT_REFERENCES

, which checks for violations of purity rules. To be callable from SQL statements, a function must obey rules that control side effects. If any SQL statement inside the function body violates a rule, you get an error at run time (when the statement is parsed). For the syntax of the pragma, see

"RESTRICT_REFERENCES Pragma" on page 13-98.

The pragma asserts that a function does not read and/or write database tables and/or package variables. For more information about the purity rules and pragma

RESTRICT_REFERENCES

, see Oracle Database Application Developer's Guide -

Fundamentals.

PRAGMA SERIALLY_REUSABLE

Marks a package as serially reusable, if its state is needed only for the duration of one call to the server (for example, an OCI call to the server or a server-to-server remote procedure call). For more information, see Oracle Database Application Developer's Guide

- Fundamentals.

procedure_body

Implements a procedure. For the syntax of procedure_body

, see

"Procedure

Declaration" on page 13-90.

procedure_spec

Declares the interface to a procedure. For the syntax of procedure_spec

, see

"Procedure Declaration" on page 13-90.

record_declaration

Declares a user-defined record. For the syntax of record_declaration

, see "Record

Definition" on page 13-95.

PL/SQL Language Elements

13-87

Package Declaration

record_type_definition

Defines a record type using the datatype specifier

RECORD

or the attribute

%ROWTYPE

schema_name

The schema containing the package. If you omit schema_name

, Oracle assumes the package is in your schema.

variable_declaration

Declares a variable. For the syntax of variable_declaration

, see "Constant and

Example 1–13, "Creating a Package and Package Body" on page 1-14

Usage Notes

You can use any Oracle tool that supports PL/SQL to create and store packages in an

Oracle database. You can issue the

CREATE PACKAGE

and

CREATE PACKAGE BODY statements interactively from SQL*Plus, or from an Oracle Precompiler or OCI host program. However, you cannot define packages in a PL/SQL block or subprogram.

Most packages have a specification and a body. The specification is the interface to your applications; it declares the types, variables, constants, exceptions, cursors, and subprograms available for use. The body fully defines cursors and subprograms, and so implements the spec.

Only subprograms and cursors have an underlying implementation. If a specification declares only types, constants, variables, exceptions, and call specifications, the package body is unnecessary. The body can still be used to initialize items declared in the specification:

CREATE OR REPLACE PACKAGE emp_actions AS

-- additional code here ...

number_hired INTEGER;

END emp_actions;

CREATE OR REPLACE PACKAGE BODY emp_actions AS

BEGIN

number_hired := 0;

END emp_actions;

You can code and compile a spec without its body. Once the spec has been compiled, stored subprograms that reference the package can be compiled as well. You do not need to define the package bodies fully until you are ready to complete the application. You can debug, enhance, or replace a package body without changing the package spec, which saves you from recompiling subprograms that call the package.

Cursors and subprograms declared in a package spec must be defined in the package body. Other program items declared in the package spec cannot be redeclared in the package body.

To match subprogram specs and bodies, PL/SQL does a token-by-token comparison of their headers. Except for white space, the headers must match word for word.

Otherwise, PL/SQL raises an exception.

Variables declared in a package keep their values throughout a session, so you can set the value of a package variable in one procedure, and retrieve the same value in a different procedure.

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Package Declaration

Examples

For examples, see the following:

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Example 9–3, "Creating the emp_admin Package" on page 9-6

Example 9–4, "Using PUT_LINE in the DBMS_OUTPUT Package" on page 9-9

Example 12–18, "TEAMS Package Using Dynamic SQL for Object Types and

Collections" on page 12-11

Related Topics

"Collection Definition" on page 13-17

"Record Definition" on page 13-95

PL/SQL Language Elements

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Procedure Declaration

A procedure is a subprogram that can take parameters and be called. Generally, you use a procedure to perform an action. A procedure has two parts: the specification and the body. The specification (spec for short) begins with the keyword

PROCEDURE

and ends with the procedure name or a parameter list. Parameter declarations are optional.

Procedures that take no parameters are written without parentheses. The procedure body begins with the keyword

(or

) and ends with the keyword

END

followed by an optional procedure name.

The procedure body has three parts: an optional declarative part, an executable part, and an optional exception-handling part. The declarative part contains declarations of types, cursors, constants, variables, exceptions, and subprograms. These items are local and cease to exist when you exit the procedure. The executable part contains statements that assign values, control execution, and manipulate Oracle data. The exception-handling part contains handlers that deal with exceptions raised during

execution. For more information, see "Understanding PL/SQL Procedures" on

page 8-3. For an example of a procedure declaration, see Example 9–3 on page 9-6.

Note that the procedure declaration in a PL/SQL block or package is not the same as creating a procedure in SQL. For information on the

CREATE PROCEDURE

SQL statement, see Oracle Database SQL Reference.

Syntax

procedure specification ::=

( parameter_declaration )

PROCEDURE procedure_name ;

procedure declaration ::=

( parameter_declaration )

PROCEDURE procedure_name

procedure body ::=

PRAGMA AUTONOMOUS_TRANSACTION ; type_definition item_declaration

EXCEPTION exception_handler function_declaration procedure_declaration

BEGIN statement

END procedure_name

;

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Procedure Declaration

parameter declaration ::=

OUT

IN OUT parameter_name

DEFAULT expression

NOCOPY datatype

Keyword and Parameter Description

datatype

A type specifier. For the syntax of datatype

, see

"Constant and Variable Declaration" on page 13-25.

exception_handler

Associates an exception with a sequence of statements, which is executed when that exception is raised. For the syntax of exception_handler

, see

Declaration" on page 13-59.

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the declaration is elaborated, the value of expression

is assigned to the parameter. The value and the parameter must have compatible datatypes.

function_declaration

Declares a function. For the syntax of function_declaration

, see

"Function

IN, OUT, IN OUT

Parameter modes that define the behavior of formal parameters. An

parameter passes values to the subprogram being called. An

OUT

parameter returns values to the caller of the subprogram. An

IN OUT

parameter lets passes initial values to the subprogram being called and returns updated values to the caller.

item_declaration

Declares a program object. For the syntax of item_declaration

, see "Block

Declaration" on page 13-8.

NOCOPY

A compiler hint (not directive) that allows the PL/SQL compiler to pass

OUT

and

OUT

parameters by reference instead of by value (the default). For more information,

see "Specifying Subprogram Parameter Modes" on page 8-7.

PL/SQL Language Elements

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Procedure Declaration

Usage Notes

A procedure is called as a PL/SQL statement. For example, the procedure raise_salary

might be called as follows: raise_salary(emp_num, amount);

Inside a procedure, an

parameter acts like a constant; you cannot assign it a value.

OUT

parameter acts like a local variable; you can change its value and reference the value in any way. An

IN OUT

parameter acts like an initialized variable; you can assign it a value, which can be assigned to another variable. For summary information about the parameter modes, see

Table 8–1 on page 8-9.

Unlike

OUT

and

IN OUT

parameters,

parameters can be initialized to default values.

For more information, see

"Using Default Values for Subprogram Parameters" on page 8-9.

Before exiting a procedure, explicitly assign values to all

OUT

formal parameters. An

OUT

actual parameter can have a value before the subprogram is called. However, when you call the subprogram, the value is lost unless you specify the compiler hint

NOCOPY

or the subprogram exits with an unhandled exception.

You can write the procedure spec and body as a unit. Or, you can separate the procedure spec from its body. That way, you can hide implementation details by placing the procedure in a package. You can define procedures in a package body without declaring their specs in the package spec. However, such procedures can be called only from inside the package. At least one statement must appear in the executable part of a procedure. The

NULL

statement meets this requirement.

Examples

parameter_name

A formal parameter, which is a variable declared in a procedure spec and referenced in the procedure body.

PRAGMA AUTONOMOUS_TRANSACTION

"Doing Independent Units of

Work with Autonomous Transactions" on page 6-37.

procedure_name

A user-defined procedure.

type_definition

Specifies a user-defined datatype. For the syntax of type_definition

, see

"Block

Declaration" on page 13-8.

:= | DEFAULT

Initializes

parameters to default values, if they are not specified when the procedure is called.

For examples, see the following:

Example 1–12, "Creating a Stored Subprogram" on page 1-13

Example 1–13, "Creating a Package and Package Body" on page 1-14

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Example 1–14, "Calling a Procedure in a Package" on page 1-15

Example 9–3, "Creating the emp_admin Package" on page 9-6

Related Topics

"Collection Methods" on page 13-20

information, see "Defining Your Own PL/SQL Exceptions" on page 10-5.

Procedure Declaration

PL/SQL Language Elements

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RAISE Statement

The

RAISE

statement stops normal execution of a PL/SQL block or subprogram and transfers control to an exception handler.

RAISE

statements can raise predefined exceptions, such as

ZERO_DIVIDE

NO_DATA_FOUND

, or user-defined exceptions whose names you decide. For more

Syntax

raise statement ::=

exception_name

RAISE ;

Keyword and Parameter Description

exception_name

A predefined or user-defined exception. For a list of the predefined exceptions, see

"Summary of Predefined PL/SQL Exceptions" on page 10-4.

Usage Notes

PL/SQL blocks and subprograms should

RAISE

an exception only when an error makes it impractical to continue processing. You can code a

RAISE

statement for a given exception anywhere within the scope of that exception.

When an exception is raised, if PL/SQL cannot find a handler for it in the current block, the exception propagates to successive enclosing blocks, until a handler is found or there are no more blocks to search. If no handler is found, PL/SQL returns an unhandled exception

error to the host environment.

In an exception handler, you can omit the exception name in a

RAISE

statement, which raises the current exception again. This technique allows you to take some initial corrective action (perhaps just logging the problem), then pass control to another handler that does more extensive correction. When an exception is reraised, the first block searched is the enclosing block, not the current block.

Examples

For examples, see the following:

Example 1–12, "Creating a Stored Subprogram" on page 1-13

Example 9–3, "Creating the emp_admin Package" on page 9-6

Example 10–3, "Scope of PL/SQL Exceptions" on page 10-6

Example 10–9, "Reraising a PL/SQL Exception" on page 10-12

Related Topics

type in C, C++, or Java. For more information, see "Understanding PL/SQL

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Record Definition

Records are composite variables that can store data values of different types, similar to a struct

Records" on page 5-5.

In PL/SQL records are useful for holding data from table rows, or certain columns from table rows. For ease of maintenance, you can declare variables as table%ROWTYPE or cursor%ROWTYPE instead of creating new record types.

Syntax

record type definition ::=

TYPE type_name IS_RECORD field_declaration ;

record field declaration ::=

NOT_NULL field_name datatype

record type declaration ::=

record_name type_name ;

DEFAULT expression

Keyword and Parameter Description

datatype

A datatype specifier. For the syntax of datatype

, see

"Constant and Variable

Declaration" on page 13-25.

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. For the syntax of expression

, see

"Expression Definition" on page 13-45. When the declaration is elaborated, the value of

expression

is assigned to the field. The value and the field must have compatible datatypes.

field_name

A field in a user-defined record.

NOT NULL

At run time, trying to assign a null to a field defined as

NOT NULL

raises the predefined exception

VALUE_ERROR

. The constraint

NOT NULL

must be followed by an initialization clause.

PL/SQL Language Elements

13-95

Record Definition

record_name

A user-defined record.

type_name

A user-defined record type that was defined using the datatype specifier

RECORD

:= | DEFAULT

Initializes fields to default values.

Usage Notes

You can define

RECORD

types and declare user-defined records in the declarative part of any block, subprogram, or package.

A record can be initialized in its declaration. You can use the

%TYPE

attribute to specify the datatype of a field. You can add the

NOT NULL

constraint to any field declaration to prevent the assigning of nulls to that field. Fields declared as

NOT NULL must be initialized. To reference individual fields in a record, you use dot notation. For example, to reference the dname

field in the dept_rec

record, you would use dept_rec.dname

Instead of assigning values separately to each field in a record, you can assign values to all fields at once:

■

You can assign one user-defined record to another if they have the same datatype.

(Having fields that match exactly is not enough.) You can assign a

%ROWTYPE record to a user-defined record if their fields match in number and order, and corresponding fields have compatible datatypes.

■

You can use the

SELECT

FETCH

statement to fetch column values into a record.

The columns in the select-list must appear in the same order as the fields in your record.

User-defined records follow the usual scoping and instantiation rules. In a package, they are instantiated when you first reference the package and cease to exist when you end the database session. In a block or subprogram, they are instantiated when you enter the block or subprogram and cease to exist when you exit the block or subprogram.

Like scalar variables, user-defined records can be declared as the formal parameters of procedures and functions. The restrictions that apply to scalar parameters also apply to user-defined records.

You can specify a

RECORD

type in the

RETURN

clause of a function spec. That allows the function to return a user-defined record of the same type. When calling a function that returns a user-defined record, use the following syntax to reference fields in the record: function_name(parameter_list).field_name

To reference nested fields, use this syntax: function_name(parameter_list).field_name.nested_field_name

If the function takes no parameters, code an empty parameter list. The syntax follows: function_name().field_name

Examples

For examples, see the following:

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Record Definition

Example 1–16, "Declaring a Record Type" on page 1-17

Example 5–8, "VARRAY of Records" on page 5-9

Example 5–20, "Assigning Values to VARRAYs with Complex Datatypes" on page 5-15

Example 5–21, "Assigning Values to Tables with Complex Datatypes" on page 5-15

Example 5–41, "Declaring and Initializing a Simple Record Type" on page 5-29

Example 5–42, "Declaring and Initializing Record Types" on page 5-29

Example 5–44, "Returning a Record from a Function" on page 5-31

Example 5–45, "Using a Record as Parameter to a Procedure" on page 5-31

Example 5–46, "Declaring a Nested Record" on page 5-31

Example 5–47, "Assigning Default Values to a Record" on page 5-32

Example 5–50, "Inserting a PL/SQL Record Using %ROWTYPE" on page 5-34

Example 5–51, "Updating a Row Using a Record" on page 5-34

Example 5–52, "Using the RETURNING Clause with a Record" on page 5-35

Example 5–53, "Using BULK COLLECT With a SELECT INTO Statement" on page 5-36

Example 6–26, "Cursor Variable Returning a Record Type" on page 6-21

Example 9–3, "Creating the emp_admin Package" on page 9-6

Related Topics

"Collection Definition" on page 13-17

"Controlling Side Effects of PL/SQL Subprograms" on page 8-23. The fewer side-effects a function has, the better it can be optimized within a

PL/SQL Language Elements

13-97

RESTRICT_REFERENCES Pragma

To be callable from SQL statements, a stored function must obey certain purity rules, which control side-effects. See

query, particular when the

PARALLEL_ENABLE

DETERMINISTIC

hints are used.

The same rules that apply to the function itself also apply to any functions or procedures that it calls.

If any SQL statement inside the function body violates a rule, you get an error at run time (when the statement is parsed). To check for violations of the rules at compile time, you can use the compiler directive

PRAGMA RESTRICT_REFERENCES

. This pragma asserts that a function does not read and/or write database tables and/or package variables. Functions that do any of these read or write operations are difficult to optimize, because any call might produce different results or encounter errors.

For more information, see Oracle Database Application Developer's Guide - Fundamentals.

Syntax

restrict_references pragma ::=

PRAGMA RESTRICT_REFERENCES ( function_name

DEFAULT

RNDS

WNDS

RNPS

WNPS

TRUST

Keyword and Parameter Description

DEFAULT

Specifies that the pragma applies to all subprograms in the package spec or object type spec. You can still declare the pragma for individual subprograms. Such pragmas override the default pragma.

function_name

A user-defined function or procedure.

PRAGMA

Signifies that the statement is a compiler directive. Pragmas are processed at compile time, not at run time. They do not affect the meaning of a program; they convey information to the compiler.

RNDS

Asserts that the subprogram reads no database state (does not query database tables).

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RESTRICT_REFERENCES Pragma

RNPS

Asserts that the subprogram reads no package state (does not reference the values of packaged variables)

TRUST

Asserts that the subprogram can be trusted not to violate one or more rules. This value is needed for functions written in C or Java that are called from PL/SQL, since

PL/SQL cannot verify them at run time.

WNDS

Asserts that the subprogram writes no database state (does not modify tables).

WNPS

Asserts that the subprogram writes no package state (does not change the values of packaged variables).

Usage Notes

You can declare the pragma

RESTRICT_REFERENCES

only in a package spec or object type spec. You can specify up to four constraints (

RNDS

RNPS

WNDS

WNPS

) in any order. To call a function from parallel queries, you must specify all four constraints. No constraint implies another. Typically, this pragma is specified for functions. If a function calls procedures, then specify the pragma for those procedures as well.

When you specify

TRUST

, the function body is not checked for violations of the constraints listed in the pragma. The function is trusted not to violate them. Skipping these checks can improve performance.

If you specify

DEFAULT

instead of a subprogram name, the pragma applies to all subprograms in the package spec or object type spec (including the system-defined constructor for object types). You can still declare the pragma for individual subprograms, overriding the default pragma.

RESTRICT_REFERENCES

pragma can apply to only one subprogram declaration. A pragma that references the name of overloaded subprograms always applies to the most recent subprogram declaration.

Examples

For examples, see the following:

Example 6–48, "Calling an Autonomous Function" on page 6-42

"SERIALLY_REUSABLE Pragma" on page 13-111

PL/SQL Language Elements

13-99

RETURN Statement

The

RETURN

statement immediately completes the execution of a subprogram and returns control to the caller. Execution resumes with the statement following the subprogram call. In a function, the

RETURN

statement also sets the function identifier

to the return value. See "Using the RETURN Statement" on page 8-5.

Syntax

return statement ::=

(

RETURN expression

)

;

Keyword and Parameter Description

expression

A combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the

RETURN

statement is executed, the value of expression

is assigned to the function identifier.

Usage Notes

The

RETURN

statement is different than the

RETURN

clause in a function spec, which specifies the datatype of the return value.

A subprogram can contain several

RETURN

statements. Executing any of them completes the subprogram immediately. The

RETURN

statement might not be positioned as the last statement in the subprogram. The

RETURN

statement can be used in an anonymous block to exit the block and all enclosing blocks, but the

RETURN statement cannot contain an expression.

In procedures, a

RETURN

statement cannot contain an expression. The statement just returns control to the caller before the normal end of the procedure is reached. In functions, a

RETURN

statement must contain an expression, which is evaluated when the

RETURN

statement is executed. The resulting value is assigned to the function identifier. In functions, there must be at least one execution path that leads to a

RETURN

statement. Otherwise, PL/SQL raises an exception at run time.

Examples

For examples, see the following:

Example 1–13, "Creating a Package and Package Body" on page 1-14

Example 2–15, "Using a Subprogram Name for Name Resolution" on page 2-15

Example 5–44, "Returning a Record from a Function" on page 5-31

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Example 6–48, "Calling an Autonomous Function" on page 6-42

Example 9–3, "Creating the emp_admin Package" on page 9-6

Related Topics

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RETURNING INTO Clause

The returning clause specifies the values return from

DELETE

EXECUTE IMMEDIATE

INSERT

, and

UPDATE

statements. You can retrieve the column values into individual variables or into collections. You cannot use the

RETURNING

clause for remote or parallel deletes. If the statement does not affect any rows, the values of the variables specified in the

RETURNING

clause are undefined.

Syntax

returning clause ::=

, single_row_expression INTO

: variable_name host_variable_name

RETURNING

RETURN , multiple_row_expression

BULK COLLECT

INTO

, collection_name

: host_array_name

Keyword and Parameter Description

BULK COLLECT

Stores result values in one or more collections, for faster queries than loops with

FETCH

statements. For more information, see

Statements and Queries with Bulk SQL" on page 11-8.

collection_name

A declared collection into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible collection in the list.

host_array_name

An array (declared in a PL/SQL host environment and passed to PL/SQL as a bind variable) into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible array in the list. Host arrays must be prefixed with a colon.

host_variable_name

INTO ...

INTO

clause.

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RETURNING INTO Clause

multiple_row_expression

Expression that returns multiple rows of a table.

RETURNING | RETURN

Used only for DML statements that have a RETURNING clause (without a BULK

COLLECT clause), this clause specifies the bind variables into which column values are returned. For each value returned by the DML statement, there must be a corresponding, type-compatible variable in the RETURNING INTO clause

single_row_expression

Expression that returns a single row of a table.

variable_name

A variable that stores a selected column value.

Usage

For DML statements that have a

RETURNING

clause, you can place

OUT

arguments in the

RETURNING INTO

clause without specifying the parameter mode, which, by definition, is

OUT

. If you use both the

USING

clause and the

RETURNING INTO

clause, the

USING

clause can contain only

arguments.

At run time, bind arguments replace corresponding placeholders in the dynamic string. Every placeholder must be associated with a bind argument in the

USING clause and/or

RETURNING INTO

clause. You can use numeric, character, and string literals as bind arguments, but you cannot use Boolean literals (

TRUE

FALSE

, and

NULL

). To pass nulls to the dynamic string, you must use a workaround. See

"Passing

Nulls to Dynamic SQL" on page 7-10.

Dynamic SQL supports all the SQL datatypes. For example, define variables and bind arguments can be collections,

LOB s, instances of an object type, and refs. Dynamic SQL does not support PL/SQL-specific types. For example, define variables and bind arguments cannot be

BOOLEAN s or index-by tables. The only exception is that a

PL/SQL record can appear in the

INTO

clause.

Examples

For examples, see the following:

Example 5–52, "Using the RETURNING Clause with a Record" on page 5-35

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

Example 7–5, "Dynamic SQL with RETURNING BULK COLLECT INTO Clause" on page 7-6

Example 7–6, "Dynamic SQL Inside FORALL Statement" on page 7-7

Example 11–15, "Using BULK COLLECT With the RETURNING INTO Clause" on page 11-18

Example 11–16, "Using FORALL With BULK COLLECT" on page 11-19

Related Topics

"DELETE Statement" on page 13-36

"UPDATE Statement" on page 13-121

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ROLLBACK Statement

The

ROLLBACK

statement is the inverse of the

COMMIT

statement. It undoes some or all database changes made during the current transaction. For more information, see

"Overview of Transaction Processing in PL/SQL" on page 6-30.

The SQL

ROLLBACK

statement can be embedded as static SQL in PL/SQL. For syntax details on the SQL

ROLLBACK

statement, see Oracle Database SQL Reference.

Usage Notes

All savepoints marked after the savepoint to which you roll back are erased. The savepoint to which you roll back is not erased. For example, if you mark savepoints A,

B, C, and D in that order, then roll back to savepoint B, only savepoints C and D are erased.

An implicit savepoint is marked before executing an

INSERT

UPDATE

, or

DELETE statement. If the statement fails, a rollback to this implicit savepoint is done. Normally, just the failed SQL statement is rolled back, not the whole transaction. If the statement raises an unhandled exception, the host environment determines what is rolled back.

Examples

For examples, see the following:

Example 2–14, "Using a Block Label for Name Resolution" on page 2-14

Example 6–38, "Using SAVEPOINT With ROLLBACK" on page 6-31

Example 6–39, "Reusing a SAVEPOINT With ROLLBACK" on page 6-32

Related Topics

"SAVEPOINT Statement" on page 13-106

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%ROWTYPE Attribute

The

%ROWTYPE

attribute provides a record type that represents a row in a database table. The record can store an entire row of data selected from the table or fetched from a cursor or cursor variable. Variables declared using

%ROWTYPE

are treated like those declared using a datatype name. You can use the

%ROWTYPE

attribute in variable declarations as a datatype specifier.

Fields in a record and corresponding columns in a row have the same names and datatypes. However, fields in a

%ROWTYPE

record do not inherit constraints, such as the

NOT NULL

column or check constraint, or default values. For more information, see

"Using the %ROWTYPE Attribute" on page 2-11.

Syntax

%rowtype attribute ::=

cursor_name cursor_variable_name table_name

% ROWTYPE

Keyword and Parameter Description

cursor_name

An explicit cursor previously declared within the current scope.

cursor_variable_name

A PL/SQL strongly typed cursor variable, previously declared within the current scope.

table_name

A database table or view that must be accessible when the declaration is elaborated.

Usage Notes

Declaring variables as the type table_name

%ROWTYPE

is a convenient way to transfer data between database tables and PL/SQL. You create a single variable rather than a separate variable for each column. You do not need to know the name of every column. You refer to the columns using their real names instead of made-up variable names. If columns are later added to or dropped from the table, your code can keep working without changes.

To reference a field in the record, use dot notation ( record_name.field_name

). You can read or write one field at a time this way.

There are two ways to assign values to all fields in a record at once:

■

First, PL/SQL allows aggregate assignment between entire records if their declarations refer to the same table or cursor.

You can assign a list of column values to a record by using the

SELECT

FETCH statement. The column names must appear in the order in which they were

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%ROWTYPE Attribute declared. Select-items fetched from a cursor associated with

%ROWTYPE

must have simple names or, if they are expressions, must have aliases.

Examples

For examples, see the following:

Example 1–6, "Using %ROWTYPE with an Explicit Cursor" on page 1-9

Example 2–8, "Using %ROWTYPE With Table Rows" on page 2-11

Example 2–9, "Using the %ROWTYPE Attribute" on page 2-11

Example 2–10, "Assigning Values to a Record With a %ROWTYPE Declaration" on page 2-12

Example 3–11, "Using SUBTYPE With %TYPE and %ROWTYPE" on page 3-20

Example 5–7, "Specifying Collection Element Types with %TYPE and %ROWTYPE" on page 5-9

Example 5–20, "Assigning Values to VARRAYs with Complex Datatypes" on page 5-15

Example 5–42, "Declaring and Initializing Record Types" on page 5-29

Example 6–24, "Cursor Variable Returning a %ROWTYPE Variable" on page 6-21

Example 6–25, "Using the %ROWTYPE Attribute to Provide the Datatype" on page 6-21

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

Processing in PL/SQL" on page 6-30.

PL/SQL Language Elements

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SAVEPOINT Statement

The

SAVEPOINT

statement names and marks the current point in the processing of a transaction. With the

ROLLBACK TO

statement, savepoints undo parts of a transaction instead of the whole transaction. For more information, see

"Overview of Transaction

The SQL

SAVEPOINT

statement can be embedded as static SQL in PL/SQL. For syntax details on the SQL

SAVEPOINT

statement, see Oracle Database SQL Reference.

Usage Notes

A simple rollback or commit erases all savepoints. When you roll back to a savepoint, any savepoints marked after that savepoint are erased. The savepoint to which you roll back remains.

You can reuse savepoint names within a transaction. The savepoint moves from its old position to the current point in the transaction.

If you mark a savepoint within a recursive subprogram, new instances of the

SAVEPOINT

statement are executed at each level in the recursive descent. You can only roll back to the most recently marked savepoint.

An implicit savepoint is marked before executing an

INSERT

UPDATE

, or

DELETE statement. If the statement fails, a rollback to the implicit savepoint is done. Normally, just the failed SQL statement is rolled back, not the whole transaction; if the statement raises an unhandled exception, the host environment (such as SQL*Plus) determines what is rolled back.

Examples

For examples, see the following:

Example 6–38, "Using SAVEPOINT With ROLLBACK" on page 6-31

Example 6–39, "Reusing a SAVEPOINT With ROLLBACK" on page 6-32

Related Topics

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SELECT INTO Statement

The

SELECT INTO

statement retrieves data from one or more database tables, and assigns the selected values to variables or collections. For a full description of the

SELECT

SQL statement, see Oracle Database SQL Reference.

In its default usage (

SELECT ... INTO

), this statement retrieves one or more columns from a single row. In its bulk usage (

SELECT ... BULK COLLECT INTO

), this statement retrieves an entire result set at once.

Syntax

select into statement ::=

DISTINCT

UNIQUE

ALL

SELECT

, select_item

INTO variable_name record_name

FROM table_reference

THE

( subquery ) alias rest_of_statement ;

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SELECT INTO Statement

select item ::=

function_name

NULL numeric_literal schema_name .

( parameter_name table_name view_name schema_name .

table_name view_name

)

, column_name sequence_name .

’ subquery text ’

CURRVAL

NEXTVAL

AS alias

Keyword and Parameter Description

alias

Another (usually short) name for the referenced column, table, or view.

BULK COLLECT

Stores result values in one or more collections, for faster queries than loops with

FETCH

statements. For more information, see

Statements and Queries with Bulk SQL" on page 11-8.

collection_name

A declared collection into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible collection in the list.

function_name

A user-defined function.

host_array_name

An array (declared in a PL/SQL host environment and passed to PL/SQL as a bind variable) into which select_item

values are fetched. For each select_item

, there must be a corresponding, type-compatible array in the list. Host arrays must be prefixed with a colon.

numeric_literal

A literal that represents a number or a value implicitly convertible to a number.

parameter_name

A formal parameter of a user-defined function.

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SELECT INTO Statement

Usage Notes

By default, a

SELECT INTO

statement must return only one row. Otherwise, PL/SQL raises the predefined exception

TOO_MANY_ROWS

and the values of the variables in the

INTO

clause are undefined. Make sure your

WHERE

clause is specific enough to only match one row

If no rows are returned, PL/SQL raises

NO_DATA_FOUND

. You can guard against this exception by selecting the result of an aggregate function, such as

COUNT(*)

AVG()

, where practical. These functions are guaranteed to return a single value, even if no rows match the condition.

SELECT ... BULK COLLECT INTO

statement can return multiple rows. You must set up collection variables to hold the results. You can declare associative arrays or nested tables that grow as needed to hold the entire result set.

The implicit cursor

SQL

and its attributes

%NOTFOUND

%FOUND

%ROWCOUNT

, and

%ISOPEN

provide information about the execution of a

SELECT INTO

statement.

Examples

record_name

A user-defined or

%ROWTYPE

record into which rows of values are fetched. For each select_item

value returned by the query, there must be a corresponding, type-compatible field in the record.

rest_of_statement

Anything that can follow the

FROM

clause in a SQL

SELECT

statement (except the

SAMPLE

clause).

schema_name

The schema containing the table or view. If you omit schema_name

, Oracle assumes the table or view is in your schema.

subquery

SELECT

statement that provides a set of rows for processing. Its syntax is similar to that of select_into_statement

without the

INTO

clause.

table_reference

A table or view that must be accessible when you execute the

SELECT

statement, and for which you must have

SELECT

privileges. For the syntax of table_reference

see "DELETE Statement" on page 13-36.

TABLE (subquery2)

The operand of

TABLE

is a

SELECT

statement that returns a single column value, which must be a nested table or a varray. Operator

TABLE

informs Oracle that the value is a collection, not a scalar value.

variable_name

A previously declared variable into which a select_item

value is fetched. For each select_item

value returned by the query, there must be a corresponding, type-compatible variable in the list.

Example 13–4 shows various ways to use the

SELECT INTO

statement.

PL/SQL Language Elements

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SELECT INTO Statement

Example 13–4 Using the SELECT INTO Statement

DECLARE

deptid employees.department_id%TYPE;

jobid employees.job_id%TYPE;

emp_rec employees%ROWTYPE;

TYPE emp_tab IS TABLE OF employees%ROWTYPE INDEX BY PLS_INTEGER;

all_emps emp_tab;

BEGIN

SELECT department_id, job_id INTO deptid, jobid

FROM employees WHERE employee_id = 140;

IF SQL%FOUND THEN

DBMS_OUTPUT.PUT_LINE('Dept Id: ' || deptid || ', Job Id: ' || jobid);

END IF;

SELECT * INTO emp_rec FROM employees WHERE employee_id = 105;

SELECT * BULK COLLECT INTO all_emps FROM employees;

DBMS_OUTPUT.PUT_LINE('Number of rows: ' || SQL%ROWCOUNT);

END;

For examples, see the following:

Example 1–3, "Assigning Values to Variables by SELECTing INTO" on page 1-6

Example 1–4, "Assigning Values to Variables as Parameters of a Subprogram" on page 1-7

Example 1–9, "Using WHILE-LOOP for Control" on page 1-11

Example 5–51, "Updating a Row Using a Record" on page 5-34

Example 5–52, "Using the RETURNING Clause with a Record" on page 5-35

Example 6–5, "Using CURRVAL and NEXTVAL" on page 6-4

Example 6–38, "Using SAVEPOINT With ROLLBACK" on page 6-31

Example 6–43, "Declaring an Autonomous Function in a Package" on page 6-38

Example 7–2, "Dynamic SQL Procedure that Accepts Table Name and WHERE Clause" on page 7-4

Related Topics

"Assignment Statement" on page 13-3

"%ROWTYPE Attribute" on page 13-104

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SERIALLY_REUSABLE Pragma

The pragma

SERIALLY_REUSABLE

indicates that the package state is needed only for the duration of one call to the server. An example could be an OCI call to the database or a stored procedure call through a database link. After this call, the storage for the package variables can be reused, reducing the memory overhead for long-running sessions. For more information, see Oracle Database Application Developer's Guide -

Fundamentals.

Syntax

pragma serially_resuable ::=

PRAGMA SERIALLY_REUSABLE ;

Keyword and Parameter Description

PRAGMA

Signifies that the statement is a pragma (compiler directive). Pragmas are processed at compile time, not at run time. They do not affect the meaning of a program; they simply convey information to the compiler.

Usage Notes

This pragma is appropriate for packages that declare large temporary work areas that are used once and not needed during subsequent database calls in the same session.

You can mark a bodiless package as serially reusable. If a package has a spec and body, you must mark both. You cannot mark only the body.

The global memory for serially reusable packages is pooled in the System Global Area

(SGA), not allocated to individual users in the User Global Area (UGA). That way, the package work area can be reused. When the call to the server ends, the memory is returned to the pool. Each time the package is reused, its public variables are initialized to their default values or to

NULL

Serially reusable packages cannot be accessed from database triggers or other PL/SQL subprograms that are called from SQL statements. If you try, Oracle generates an error.

Examples

Example 13–5 creates a serially reusable package.

Example 13–5 Creating a Serially Reusable Package

CREATE PACKAGE pkg1 IS

PRAGMA SERIALLY_REUSABLE;

num NUMBER := 0;

PROCEDURE init_pkg_state(n NUMBER);

PROCEDURE print_pkg_state;

END pkg1;

CREATE PACKAGE BODY pkg1 IS

PRAGMA SERIALLY_REUSABLE;

PROCEDURE init_pkg_state (n NUMBER) IS

PL/SQL Language Elements

13-111

SERIALLY_REUSABLE Pragma

BEGIN

pkg1.num := n;

END;

PROCEDURE print_pkg_state IS

BEGIN

DBMS_OUTPUT.PUT_LINE('Num: ' || pkg1.num);

END;

END pkg1;

"RESTRICT_REFERENCES Pragma" on page 13-98

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SET TRANSACTION Statement

The

SET TRANSACTION

statement begins a read-only or read-write transaction, establishes an isolation level, or assigns the current transaction to a specified rollback segment. Read-only transactions are useful for running multiple queries against one or more tables while other users update the same tables. For more information, see

"Setting Transaction Properties with SET TRANSACTION" on page 6-33.

For additional information on the

SET TRANSACTION

SQL statement, see Oracle

Database SQL Reference.

Syntax

SET

set transaction ::=

TRANSACTION

READ

ONLY

WRITE

ISOLATION LEVEL

SERIALIZABLE

READ COMMITTED

USE ROLLBACK SEGMENT rollback_segment_name

NAME ’ text ’

;

Keyword and Parameter Description

READ ONLY

Establishes the current transaction as read-only, so that subsequent queries see only changes committed before the transaction began. The use of

READ ONLY

does not affect other users or transactions.

READ WRITE

Establishes the current transaction as read-write. The use of

READ WRITE

does not affect other users or transactions. If the transaction executes a data manipulation statement, Oracle assigns the transaction to a rollback segment.

ISOLATION LEVEL

Specifies how to handle transactions that modify the database.

SERIALIZABLE

: If a serializable transaction tries to execute a SQL data manipulation statement that modifies any table already modified by an uncommitted transaction, the statement fails.

To enable

SERIALIZABLE

mode, your DBA must set the Oracle initialization parameter

COMPATIBLE

to 7.3.0 or higher.

READ COMMITTED

: If a transaction includes SQL data manipulation statements that require row locks held by another transaction, the statement waits until the row locks are released.

USE ROLLBACK SEGMENT

Assigns the current transaction to the specified rollback segment and establishes the transaction as read-write. You cannot use this parameter with the

READ ONLY

PL/SQL Language Elements

13-113

SET TRANSACTION Statement parameter in the same transaction because read-only transactions do not generate rollback information.

NAME

Specifies a name or comment text for the transaction. This is better than using the

COMMIT COMMENT

feature because the name is available while the transaction is running, making it easier to monitor long-running and in-doubt transactions.

Usage Notes

The

SET TRANSACTION

statement must be the first SQL statement in the transaction and can appear only once in the transaction.

Examples

For examples, see the following:

Example 6–40, "Using SET TRANSACTION to Begin a Read-only Transaction" on page 6-33

Related Topics

"SAVEPOINT Statement" on page 13-106

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SQL Cursor

Oracle implicitly opens a cursor to process each SQL statement not associated with an explicit cursor. In PL/SQL, you can refer to the most recent implicit cursor as the

SQL cursor, which always has the attributes

%FOUND

%ISOPEN

%NOTFOUND

, and

%ROWCOUNT

. They provide information about the execution of data manipulation statements. The

SQL

cursor has additional attributes,

%BULK_ROWCOUNT

and

%BULK_EXCEPTIONS

, designed for use with the

FORALL

statement. For more

information, see "Querying Data with PL/SQL" on page 6-14.

Syntax

sql cursor ::=

SQL %

FOUND

ISOPEN

NOTFOUND

ROWCOUNT

BULK_ROWCOUNT ( index )

BULK_EXCEPTIONS ( index ) .

ERROR_INDEX

ERROR_CODE

Keyword and Parameter Description

%BULK_ROWCOUNT

A composite attribute designed for use with the

FORALL

statement. This attribute acts like an index-by table. Its ith element stores the number of rows processed by the ith execution of an

UPDATE

DELETE

statement. If the ith execution affects no rows,

%BULK_ROWCOUNT(i)

returns zero.

%BULK_EXCEPTIONS

An associative array that stores information about any exceptions encountered by a

FORALL

statement that uses the

SAVE EXCEPTIONS

clause. You must loop through its elements to determine where the exceptions occurred and what they were. For each index value i

between 1 and

SQL%BULK_EXCEPTIONS.COUNT

SQL%BULK_EXCEPTIONS(i).ERROR_INDEX

specifies which iteration of the

FORALL loop caused an exception.

SQL%BULK_EXCEPTIONS(i).ERROR_CODE

specifies the

Oracle error code that corresponds to the exception.

%FOUND

Returns

TRUE

if an

INSERT

UPDATE

, or

DELETE

statement affected one or more rows or a

SELECT INTO

statement returned one or more rows. Otherwise, it returns

FALSE

%ISOPEN

Always returns

FALSE

, because Oracle closes the

SQL

cursor automatically after executing its associated SQL statement.

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SQL Cursor

%NOTFOUND

The logical opposite of

%FOUND

. It returns

TRUE

if an

INSERT

UPDATE

, or

DELETE statement affected no rows, or a

SELECT INTO

statement returned no rows. Otherwise, it returns

FALSE

%ROWCOUNT

Returns the number of rows affected by an

INSERT

UPDATE

, or

DELETE

statement, or returned by a

SELECT INTO

statement.

SQL

The name of the Oracle implicit cursor.

Usage Notes

You can use cursor attributes in procedural statements but not in SQL statements.

Before Oracle opens the

SQL

cursor automatically, the implicit cursor attributes return

NULL

. The values of cursor attributes always refer to the most recently executed SQL statement, wherever that statement appears. It might be in a different scope. If you want to save an attribute value for later use, assign it to a variable immediately.

If a

SELECT INTO

statement fails to return a row, PL/SQL raises the predefined exception

NO_DATA_FOUND

, whether you check

SQL%NOTFOUND

on the next line or not. A

SELECT INTO

statement that calls a SQL aggregate function never raises

NO_DATA_FOUND

, because those functions always return a value or a

NULL

. In such cases,

SQL%NOTFOUND

returns

FALSE

%BULK_ROWCOUNT

is not maintained for bulk inserts because that would be redundant as a typical insert affects only one row. See

"Counting Rows Affected by FORALL with the %BULK_ROWCOUNT Attribute" on page 11-12.

You can use the scalar attributes

%FOUND

%NOTFOUND

, and

%ROWCOUNT

with bulk binds. For example,

%ROWCOUNT

returns the total number of rows processed by all executions of the SQL statement. Although

%FOUND

and

%NOTFOUND

refer only to the last execution of the SQL statement, you can use

%BULK_ROWCOUNT

to infer their values for individual executions. For example, when

%BULK_ROWCOUNT(i)

is zero,

%FOUND

and

%NOTFOUND

are

FALSE

and

TRUE

, respectively.

Examples

For examples, see the following:

Example 6–8, "Using SQL%ROWCOUNT" on page 6-7

Example 6–10, "Fetching With a Cursor" on page 6-10

Example 6–14, "Using %FOUND" on page 6-12

Example 6–15, "Using %ISOPEN" on page 6-12

Example 6–16, "Using %NOTFOUND" on page 6-13

Example 6–17, "Using %ROWCOUNT" on page 6-13

Example 11–7, "Using %BULK_ROWCOUNT With the FORALL Statement" on page 11-13

Example 13–4, "Using the SELECT INTO Statement" on page 13-110

Related Topics

"Cursor Attributes" on page 13-28

"FORALL Statement" on page 13-56

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SQLCODE Function

The function

SQLCODE

returns the number code of the most recent exception.

For internal exceptions,

SQLCODE

returns the number of the associated Oracle error.

The number that

SQLCODE

returns is negative unless the Oracle error is no data found, in which case

SQLCODE

returns

+100

. For user-defined exceptions,

SQLCODE

returns

, or a value you assign if the exception is associated with an Oracle error number through pragma

EXCEPTION_INIT

Syntax

sqlcode function ::=

SQLCODE

Usage Notes

SQLCODE

is only useful in an exception handler. Outside a handler,

SQLCODE

always returns

SQLCODE

is especially useful in the

OTHERS

exception handler, because it lets you identify which internal exception was raised. You cannot use

SQLCODE directly in a SQL statement. Assign the value of

SQLCODE

to a local variable first.

When using pragma

RESTRICT_REFERENCES

to assert the purity of a stored function, you cannot specify the constraints

WNPS

and

RNPS

if the function calls

SQLCODE

Examples

Example 13–6 shows the use of

SQLCODE

and

SQLERRM

Example 13–6 Using SQLCODE and SQLERRM

DECLARE

name employees.last_name%TYPE;

v_code NUMBER;

v_errm VARCHAR2(64);

BEGIN

SELECT last_name INTO name FROM employees WHERE employee_id = 1000;

EXCEPTION

WHEN OTHERS THEN

v_code := SQLCODE;

v_errm := SUBSTR(SQLERRM, 1 , 64);

DBMS_OUTPUT.PUT_LINE('The error code is ' || v_code || '- ' || v_errm);

END;

For examples, see the following:

Example 10–11, "Displaying SQLCODE and SQLERRM" on page 10-14

Related Topics

"SQLERRM Function" on page 13-118

"Retrieving the Error Code and Error Message: SQLCODE and SQLERRM" on page 10-14

PL/SQL Language Elements

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SQLERRM Function

The function

SQLERRM

returns the error message associated with its error-number argument. If the argument is omitted, it returns the error message associated with the current value of

SQLCODE

SQLERRM

with no argument is useful only in an exception handler. Outside a handler,

SQLERRM

with no argument always returns the normal, successful completion

message. For internal exceptions,

SQLERRM

returns the message associated with the Oracle error that occurred. The message begins with the

Oracle error code.

For user-defined exceptions,

SQLERRM

returns the message user-defined exception, unless you used the pragma

EXCEPTION_INIT

to associate the exception with an

Oracle error number, in which case

SQLERRM

returns the corresponding error message.

For more information, see

"Retrieving the Error Code and Error Message: SQLCODE and SQLERRM" on page 10-14.

Syntax

sqlerrm function ::=

( error_number )

SQLERRM

Keyword and Parameter Description

error_number

A valid Oracle error number. For a list of Oracle errors (ones prefixed by ORA-), see

Oracle Database Error Messages.

Usage Notes

SQLERRM

is especially useful in the

OTHERS

exception handler, where it lets you identify which internal exception was raised. The error number passed to

SQLERRM should be negative. Passing a zero to

SQLERRM

always returns the

ORA-0000: normal, successful completion

message. Passing a positive number to

SQLERRM

always returns the

User-Defined Exception

message unless you pass

+100

, in which case

SQLERRM

returns the

ORA-01403: no data found

message.

You cannot use

SQLERRM

directly in a SQL statement. Assign the value of

SQLERRM

to a local variable first, as shown in

Example 13–6 on page 13-117.

When using pragma

RESTRICT_REFERENCES

to assert the purity of a stored function, you cannot specify the constraints

WNPS

and

RNPS

if the function calls

SQLERRM

Examples

For examples, see the following:

Example 10–11, "Displaying SQLCODE and SQLERRM" on page 10-14

Example 13–6, "Using SQLCODE and SQLERRM" on page 13-117

Related Topics

"SQLCODE Function" on page 13-117

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%TYPE Attribute

The

%TYPE

attribute lets use the datatype of a field, record, nested table, database column, or variable in your own declarations, rather than hardcoding the type names.

You can use the

%TYPE

attribute as a datatype specifier when declaring constants, variables, fields, and parameters. If the types that you reference change, your declarations are automatically updated. This technique saves you from making code changes when, for example, the length of a

VARCHAR2

column is increased. Note that column constraints, such as the

NOT NULL

and check constraint, or default values are not inherited by items declared using

%TYPE

. For more information, see

"Using the

%TYPE Attribute" on page 2-10.

Syntax

%type attribute ::=

collection_name cursor_variable_name object name

field_name record_name db_table_name .

column_name variable_name

% TYPE

Keyword and Parameter Description

collection_name

A nested table, index-by table, or varray previously declared within the current scope.

cursor_variable_name

A PL/SQL cursor variable previously declared within the current scope. Only the value of another cursor variable can be assigned to a cursor variable.

db_table_name.column_name

A table and column that must be accessible when the declaration is elaborated.

object_name

An instance of an object type, previously declared within the current scope.

record_name

A user-defined or

%ROWTYPE

record, previously declared within the current scope.

record_name.field_name

A field in a user-defined or

%ROWTYPE

record, previously declared within the current scope.

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13-119

%TYPE Attribute

variable_name

A variable, previously declared in the same scope.

Usage Notes

The

%TYPE

attribute is particularly useful when declaring variables, fields, and parameters that refer to database columns. Your code can keep working even when the lengths or types of the columns change.

Examples

For examples, see the following:

Example 1–15, "Using a PL/SQL Collection Type" on page 1-16

Example 2–6, "Using %TYPE With the Datatype of a Variable" on page 2-10

Example 2–7, "Using %TYPE With Table Columns" on page 2-10

Example 2–15, "Using a Subprogram Name for Name Resolution" on page 2-15

Example 2–10, "Assigning Values to a Record With a %ROWTYPE Declaration" on page 2-12

Example 3–11, "Using SUBTYPE With %TYPE and %ROWTYPE" on page 3-20

Example 5–5, "Declaring a Procedure Parameter as a Nested Table" on page 5-8

Example 5–7, "Specifying Collection Element Types with %TYPE and %ROWTYPE" on page 5-9

Example 5–42, "Declaring and Initializing Record Types" on page 5-29

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

Example 6–13, "Fetching Bulk Data With a Cursor" on page 6-11

Example 13–1, "Declaring and Assigning Values to Variables" on page 13-5

"%ROWTYPE Attribute" on page 13-104

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Oracle Database PL/SQL User’s Guide and Reference

UPDATE Statement

The

UPDATE

statement changes the values of specified columns in one or more rows in a table or view. For a full description of the

UPDATE

SQL statement, see Oracle Database

SQL Reference.

Syntax

UPDATE

update statement ::=

table_reference

( subquery1

TABLE ( subquery2

) alias

SET column_name =

( column_name

( sql_expression subquery3 )

) = ( subquery4 )

WHERE search_condition

CURRENT_OF cursor_name returning_clause

Keyword and Parameter Description

alias

Another (usually short) name for the referenced table or view, typically used in the

WHERE

clause.

column_name

The column (or one of the columns) to be updated. It must be the name of a column in the referenced table or view. A column name cannot be repeated in the column_name list. Column names need not appear in the

UPDATE

statement in the same order that they appear in the table or view.

returning_clause

Returns values from updated rows, eliminating the need to

SELECT

the rows afterward. You can retrieve the column values into variables or host variables, or into collections or host arrays. You cannot use the

RETURNING

clause for remote or parallel updates. If the statement does not affect any rows, the values of the variables specified in the

RETURNING

clause are undefined. For the syntax of returning_clause

, see

"RETURNING INTO Clause" on page 13-101.

SET column_name = sql_expression

This clause assigns the value of sql_expression

to the column identified by column_name

. If sql_expression

contains references to columns in the table being

PL/SQL Language Elements

13-121

UPDATE Statement updated, the references are resolved in the context of the current row. The old column values are used on the right side of the equal sign.

SET column_name = (subquery3)

Assigns the value retrieved from the database by subquery3

to the column identified by column_name

. The subquery must return exactly one row and one column.

SET (column_name, column_name, ...) = (subquery4)

Assigns the values retrieved from the database by subquery4

to the columns in the column_name

list. The subquery must return exactly one row that includes all the columns listed. The column values returned by the subquery are assigned to the columns in the column list in order. The first value is assigned to the first column in the list, the second value is assigned to the second column in the list, and so on.

sql_expression

Any valid SQL expression. For more information, see Oracle Database SQL Reference.

subquery

SELECT

statement that provides a set of rows for processing. Its syntax is like that of select_into_statement

without the

INTO

clause. See

see "DELETE Statement" on page 13-36.

table_reference

A table or view that must be accessible when you execute the

UPDATE

statement, and for which you must have

UPDATE

privileges. For the syntax of table_reference

TABLE (subquery2)

The operand of

TABLE

is a

SELECT

statement that returns a single column value, which must be a nested table or a varray. Operator

TABLE

informs Oracle that the value is a collection, not a scalar value.

WHERE CURRENT OF cursor_name

Refers to the latest row processed by the

FETCH

statement associated with the specified cursor. The cursor must be

FOR UPDATE

and must be open and positioned on a row. If the cursor is not open, the

CURRENT OF

clause causes an error. If the cursor is open, but no rows have been fetched or the last fetch returned no rows, PL/SQL raises the predefined exception

NO_DATA_FOUND

WHERE search_condition

Chooses which rows to update in the database table. Only rows that meet the search condition are updated. If you omit this clause, all rows in the table are updated.

Usage Notes

You can use the

UPDATE WHERE CURRENT OF

statement after a fetch from an open cursor (including fetches done by a cursor

FOR

loop), provided the associated query is

FOR UPDATE

. This statement updates the row that was just fetched.

The implicit cursor

SQL

and the cursor attributes

%NOTFOUND

%FOUND

%ROWCOUNT

, and

%ISOPEN

let you access useful information about the execution of an

UPDATE statement.

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UPDATE Statement

Examples

Example 13–7 creates a table with correct employee IDs but garbled names. Then it

runs an

UPDATE

statement with a correlated query, to retrieve the correct names from the

EMPLOYEES

table and fix the names in the new table.

Example 13–7 Using UPDATE With a Subquery

-- Create a table with all the right IDs, but messed-up names

CREATE TABLE employee_temp AS

SELECT employee_id, UPPER(first_name) first_name,

TRANSLATE(last_name,'aeiou','12345') last_name

FROM employees;

BEGIN

-- Display the first 5 names to show they're messed up

FOR person IN (SELECT * FROM employee_temp WHERE ROWNUM < 6)

LOOP

DBMS_OUTPUT.PUT_LINE(person.first_name || ' ' || person.last_name);

END LOOP;

UPDATE employee_temp SET (first_name, last_name) =

(SELECT first_name, last_name FROM employees

WHERE employee_id = employee_temp.employee_id);

DBMS_OUTPUT.PUT_LINE('*** Updated ' || SQL%ROWCOUNT || ' rows. ***');

-- Display the first 5 names to show they've been fixed up

FOR person IN (SELECT * FROM employee_temp WHERE ROWNUM < 6)

LOOP

DBMS_OUTPUT.PUT_LINE(person.first_name || ' ' || person.last_name);

END LOOP;

END;

For examples, see the following:

Example 1–12, "Creating a Stored Subprogram" on page 1-13

Example 4–1, "Using a Simple IF-THEN Statement" on page 4-2

Example 5–51, "Updating a Row Using a Record" on page 5-34

Example 5–52, "Using the RETURNING Clause with a Record" on page 5-35

Example 6–1, "Data Manipulation With PL/SQL" on page 6-1

Example 6–5, "Using CURRVAL and NEXTVAL" on page 6-4

Example 6–6, "Using ROWNUM" on page 6-5

Example 6–38, "Using SAVEPOINT With ROLLBACK" on page 6-31

Example 6–41, "Using CURRENT OF to Update the Latest Row Fetched From a

Cursor" on page 6-35

Example 7–5, "Dynamic SQL with RETURNING BULK COLLECT INTO Clause" on page 7-6

Example 7–6, "Dynamic SQL Inside FORALL Statement" on page 7-7

Example 11–6, "Using Rollbacks With FORALL" on page 11-12

Example 11–9, "Bulk Operation That Continues Despite Exceptions" on page 11-15

Related Topics

"Data Manipulation" on page 6-1

"DELETE Statement" on page 13-36

"INSERT Statement" on page 13-66

PL/SQL Language Elements

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UPDATE Statement

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Oracle Database PL/SQL User’s Guide and Reference

Obfuscating PL/SQL Source Code

This appendix describes how to use the standalone wrap

utility and subprograms of the

DBMS_DDL

package to obfuscate, or wrap, PL/SQL source code. When you obfuscate (hide) PL/SQL units, you can deliver PL/SQL applications without exposing your source code and implementation details.

This appendix contains these topics:

■

What is Obfuscation?

■

Obfuscating PL/SQL Code With the wrap Utility

Obfuscating PL/QL Code With DBMS_DDL Subprograms

What is Obfuscation?

Obfuscation, or wrapping, of a PL/SQL unit is the process of hiding the PL/SQL source code. Wrapping can be done with the wrap

utility and

DBMS_DDL subprograms. The wrap

utility is run from the command line and processes an input

SQL file, such as a SQL*Plus installation script. The

DBMS_DDL

subprograms wrap a single PL/SQL unit, such as a single

CREATE PROCEDURE

command, that has been generated dynamically.

The advantages of obfuscating, or hiding, the source code of PL/SQL units with the wrap

utility or wrap subprograms of the

DBMS_DDL

package are:

■

It is difficult for other developers to misuse your application, or business competitors to see your algorithms.

■

Your source code is not visible through the

USER_SOURCE

ALL_SOURCE

, or

DBA_

SOURCE

data dictionary views.

SQL*Plus can process the obfuscated source files.

The Import and Export utilities accept wrapped files. You can back up or move wrapped procedures.

Tips When Obfuscating PL/SQL Units

When obfuscating (wrapping) PL/SQL units note the following:

■

When wrapping a package or object type, wrap only the body, not the specification. This allows other developers see the information they need to use the package or type, but they cannot see its implementation.

Obfuscating PL/SQL Source Code

A-1

Obfuscating PL/SQL Code With the wrap Utility

■

PL/SQL source inside wrapped files cannot be edited. To change wrapped

PL/SQL code, edit the original source file and wrap it again. You can either hold off on wrapping your code until it is ready for shipment to end-users, or include the wrapping operation as part of your build environment.

To be sure that all the important parts of your source code are obfuscated, view the wrapped file in a text editor before distributing it.

Limitations of Obfuscation

The following are limitations when obfuscating PL/SQL source code:

■

Although wrapping a compilation unit helps to hide the algorithm and makes reverse-engineering difficult, Oracle Corporation does not recommend it as a secure method for hiding passwords or table names. Obfuscating a PL/SQL unit prevents most users from examining the source code, but might not stop all attempts.

The wrapping does not obfuscate the source code for triggers. To hide the workings of a trigger, you can write a one-line trigger that calls a wrapped procedure.

Wrapping only detects tokenization errors, such as a runaway string, when obfuscating PL/SQL code. Wrapping does not detect syntax or semantic errors, such as tables or views that do not exist. Those errors are detected during PL/SQL compilation or when executing the output file in SQL*Plus.

Obfuscated PL/SQL program units cannot be imported into a database of a previous (lower) release. Wrapped compilation units are upward-compatible between Oracle releases, but are not downward-compatible. For example, you can load files processed by the V8.1.5 wrap

utility into a V8.1.6 Oracle database, but you cannot load files processed by the V8.1.6 wrap

utility into a V8.1.5 Oracle database.

■

Limitations of the wrap Utility

Because the source code is parsed by the PL/SQL compiler, not by SQL*Plus, you cannot include substitution variables using the SQL*Plus

DEFINE

notation inside the PL/SQL code. You can use substitution variables in other SQL statements that are not obfuscated.

Most of the comments are removed in wrapped files. See

"Input and Output Files for the PL/SQL wrap Utility" on page A-3.

■

Limitations of the DBMS_DDL wrap Function

If you invoke

DBMS_SQL

PARSE

(when using an overload where the statement formal has datatype

VARCHAR2A

VARCHAR2S

for text which exceeds 32767 bytes) on the output of

DBMS_DDL

WRAP

, then you need to set the

LFFLG parameter to

FALSE

. Otherwise

DBMS_SQL

PARSE

adds newlines to the wrapped unit which corrupts the unit.

Obfuscating PL/SQL Code With the wrap Utility

The wrap

utility processes an input SQL file and obfuscates only the PL/SQL units in the file, such as a package specification, package body, function, procedure, type specification, or type body. It does not obfuscate PL/SQL content in anonymous blocks or triggers or non-PL/SQL code.

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Oracle Database PL/SQL User’s Guide and Reference

Obfuscating PL/SQL Code With the wrap Utility

To run the wrap utility, enter the wrap

command at your operating system prompt using the following syntax: wrap iname=

input_file [ oname=

output_file]

Do not use any spaces around the equal signs.

input_file

is the name of a file containing SQL statements, that you typically run using SQL*Plus. If you omit the file extension, an extension of

.sql

is assumed. For example, the following commands are equivalent: wrap iname=/mydir/myfile wrap iname=/mydir/myfile.sql

You can also specify a different file extension: wrap iname=/mydir/myfile.src

output_file

is the name of the obfuscated file that is created. The oname

option is optional, because the output file name defaults to that of the input file and its extension defaults to

.plb

. For example, the following commands are equivalent: wrap iname=/mydir/myfile wrap iname=/mydir/myfile.sql oname=/mydir/myfile.plb

You can use the option oname

to specify a different file name and extension: wrap iname=/mydir/myfile oname=/yourdir/yourfile.out

Input and Output Files for the PL/SQL wrap Utility

The input file can contain any combination of SQL statements. Most statements are passed through unchanged.

CREATE

statements that define subprograms, packages, or object types are obfuscated; their bodies are replaced by a scrambled form that the

PL/SQL compiler understands.

The following CREATE statements are obfuscated:

CREATE [OR REPLACE] FUNCTION

function_name

CREATE [OR REPLACE] PROCEDURE

procedure_name

CREATE [OR REPLACE] PACKAGE

package_name

CREATE [OR REPLACE] PACKAGE BODY

package_name

CREATE [OR REPLACE] TYPE

type_name

AS OBJECT

CREATE [OR REPLACE] TYPE

type_name

UNDER

type_name

CREATE [OR REPLACE] TYPE BODY

type_name

The

CREATE [OR REPLACE] TRIGGER

statement, and

[DECLARE] BEGIN..END

anonymous blocks, are not obfuscated. All other SQL statements are passed unchanged to the output file.

All comment lines in the unit being wrapped are deleted, except for those in a

CREATE

OR REPLACE

header and C-style comments (delimited by

/* */

The output file is a text file, which you can run as a script in SQL*Plus to set up your

PL/SQL procedures, functions, and packages. Run a wrapped file as follows:

SQL> @wrapped_file_name.plb;

Running the wrap Utility

For example, assume that the wrap_test.sql

file contains the following:

Obfuscating PL/SQL Source Code

A-3

Obfuscating PL/QL Code With DBMS_DDL Subprograms

CREATE PROCEDURE wraptest IS

TYPE emp_tab IS TABLE OF employees%ROWTYPE INDEX BY PLS_INTEGER;

all_emps emp_tab;

BEGIN

SELECT * BULK COLLECT INTO all_emps FROM employees;

FOR i IN 1..10 LOOP

DBMS_OUTPUT.PUT_LINE('Emp Id: ' || all_emps(i).employee_id);

END LOOP;

END;

To wrap the file, run the following from the operating system prompt: wrap iname=wrap_test.sql

The output of the wrap

utility is similar to the following:

PL/SQL Wrapper: Release 10.2.0.0.0 on Tue Apr 26 16:47:39 2005

Processing wrap_test.sql to wrap_test.plb

If you view the contents of the wrap_test.plb

text file, the first line is

CREATE

PROCEDURE wraptest wrapped

and the rest of the file contents is hidden.

You can run wrap_test.plb

in SQL*Plus to execute the SQL statements in the file:

SQL> @wrap_test.plb

After the wrap_test.plb

is run, you can execute the procedure that was created:

SQL> CALL wraptest();

Obfuscating PL/QL Code With DBMS_DDL Subprograms

The

DBMS_DDL

package contains procedures for obfuscating a single PL/SQL unit, such as a package specification, package body, function, procedure, type specification, or type body. These overloaded subprograms provide a mechanism for obfuscating dynamically generated PL/SQL program units that are created in a database.

The

DBMS_DDL

package contains the

WRAP

function and the

CREATE_WRAPPED procedure. The

CREATE_WRAPPED

both wraps the text and creates the PL/SQL unit.

When calling the wrap procedures, use the fully-qualified package name,

SYS.DBMS_

DDL

, to avoid any naming conflicts and the possibility that someone might create a local package called

DBMS_DDL

or define the

DBMS_DDL

public synonym. The input

CREATE OR REPLACE

statement executes with the privileges of the user who invokes

DBMS_DDL.WRAP()

DBMS_DDL.CREATE_WRAPPED()

The

DBMS_DDL

package also provides the

MALFORMED_WRAP_INPUT

exception

(ORA-24230) which is raised if the input to the wrap procedures is not a valid PL/SQL unit.

Using the DBMS_DDL create_wrapped Procedure

Example A–1 illustrates how

CREATE_WRAPPED

can be used to dynamically create and wrap a package specification and a package body in a database.

Example A–1 Using the create_wrapped Procedure to Wrap a Package

DECLARE

-- the package_text variable contains the text to create the package spec and body

package_text VARCHAR2(32767);

A-4

Oracle Database PL/SQL User’s Guide and Reference

Obfuscating PL/QL Code With DBMS_DDL Subprograms

FUNCTION generate_spec (pkgname VARCHAR2) RETURN VARCHAR2 AS

BEGIN

RETURN 'CREATE PACKAGE ' || pkgname || ' AS

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER);

PROCEDURE fire_employee (emp_id NUMBER);

END ' || pkgname || ';';

END generate_spec;

FUNCTION generate_body (pkgname VARCHAR2) RETURN VARCHAR2 AS

BEGIN

RETURN 'CREATE PACKAGE BODY ' || pkgname || ' AS

PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER) IS

BEGIN

UPDATE employees SET salary = salary + amount WHERE employee_id = emp_id;

END raise_salary;

PROCEDURE fire_employee (emp_id NUMBER) IS

BEGIN

DELETE FROM employees WHERE employee_id = emp_id;

END fire_employee;

END ' || pkgname || ';';

END generate_body;

BEGIN

package_text := generate_spec('emp_actions'); -- generate package spec

SYS.DBMS_DDL.CREATE_WRAPPED(package_text); -- create and wrap the package spec

package_text := generate_body('emp_actions'); -- generate package body

SYS.DBMS_DDL.CREATE_WRAPPED(package_text); -- create and wrap the package body

END;

-- call a procedure from the wrapped package

CALL emp_actions.raise_salary(120, 100);

When you check the

*_SOURCE

views, the source is wrapped, or hidden, so that others cannot view the code details. For example:

SELECT text FROM USER_SOURCE WHERE name = 'EMP_ACTIONS';

The resulting output appears similar to:

TEXT

---------------------------------------------------------------

PACKAGE emp_actions wrapped a000000

1f abcd

...

Obfuscating PL/SQL Source Code

A-5

Obfuscating PL/QL Code With DBMS_DDL Subprograms

A-6

Oracle Database PL/SQL User’s Guide and Reference

How PL/SQL Resolves Identifier Names

This appendix explains how PL/SQL resolves references to names in potentially ambiguous SQL and procedural statements.

This appendix contains these topics:

■

What Is Name Resolution?

■

Examples of Qualified Names and Dot Notation

Differences in Name Resolution Between PL/SQL and SQL

Understanding Capture

Avoiding Inner Capture in DML Statements

Qualifying References to Object Attributes and Methods

What Is Name Resolution?

During compilation, the PL/SQL compiler determines which objects are associated with each name in a PL/SQL subprogram. A name might refer to a local variable, a table, a package, a procedure, a schema, and so on. When a subprogram is recompiled, that association might change if objects have been created or deleted.

A declaration or definition in an inner scope can hide another in an outer scope. In

Example B–1

, the declaration of variable client

hides the definition of datatype

Client

because PL/SQL names are not case sensitive:

Example B–1 Resolving Global and Local Variable Names

BEGIN

<<block1>>

DECLARE

TYPE Client IS RECORD ( first_name VARCHAR2(20), last_name VARCHAR2(25) );

TYPE Customer IS RECORD ( first_name VARCHAR2(20), last_name VARCHAR2(25) );

BEGIN

DECLARE

client Customer; -- hides definition of type Client in outer scope

-- lead1 Client; --

not allowed; Client resolves to the variable client

lead2 block1.Client; -- OK; refers to type Client

BEGIN

NULL; -- no processing, just an example of name resolution

END;

How PL/SQL Resolves Identifier Names

B-1

Examples of Qualified Names and Dot Notation

You can refer to datatype

Client

by qualifying the reference with block label block1

In the following set of

CREATE TYPE

statements, the second statement generates a warning. Creating an attribute named manager

hides the type named manager

, so the declaration of the second attribute does not execute correctly.

CREATE TYPE manager AS OBJECT (dept NUMBER);

CREATE TYPE person AS OBJECT (manager NUMBER, mgr manager) -- raises a warning;

Examples of Qualified Names and Dot Notation

During name resolution, the compiler can encounter various forms of references including simple unqualified names, dot-separated chains of identifiers, indexed components of a collection, and so on. This is shown in

Example B–2 .

Example B–2 Using the Dot Notation to Qualify Names

CREATE OR REPLACE PACKAGE pkg1 AS

m NUMBER;

TYPE t1 IS RECORD (a NUMBER);

v1 t1;

TYPE t2 IS TABLE OF t1 INDEX BY PLS_INTEGER;

v2 t2;

FUNCTION f1 (p1 NUMBER) RETURN t1;

FUNCTION f2 (q1 NUMBER) RETURN t2;

END pkg1;

CREATE OR REPLACE PACKAGE BODY pkg1 AS

FUNCTION f1 (p1 NUMBER) RETURN t1 IS

n NUMBER;

BEGIN

-- (1) unqualified name

n := m

;

-- (2) dot-separated chain of identifiers (package name used as scope

-- qualifier followed by variable name)

n := pkg1.m

;

-- (3) dot-separated chain of identifiers (package name used as scope

-- qualifier followed by function name also used as scope qualifier

-- followed by parameter name)

n := pkg1.f1.p1

;

-- (4) dot-separated chain of identifiers (variable name followed by

-- component selector)

n := v1.a

;

-- (5) dot-separated chain of identifiers (package name used as scope

-- qualifier followed by variable name followed by component selector)

n := pkg1.v1.a

;

-- (6) indexed name followed by component selector

n := v2(10).a

;

-- (7) function call followed by component selector

n := f1(10).a

;

-- (8) function call followed by indexing followed by component selector

n := f2(10)(10).a

;

-- (9) function call (which is a dot-separated chain of identifiers,

-- including schema name used as scope qualifier followed by package

-- name used as scope qualifier followed by function name)

-- followed by component selector of the returned result followed

B-2

Oracle Database PL/SQL User’s Guide and Reference

Differences in Name Resolution Between PL/SQL and SQL

-- by indexing followed by component selector

n := hr.pkg1.f2(10)(10).a

;

-- (10) variable name followed by component selector

v1.a := p1;

RETURN v1;

END f1;

FUNCTION f2 (q1 NUMBER) RETURN t2 IS

v_t1 t1;

v_t2 t2;

BEGIN

v_t1.a := q1;

v_t2(1) := v_t1;

RETURN v_t2;

END f2;

END pkg1;

Note that an outside reference to a private variable declared in a function body is not legal. For example, an outside reference to the variable n

declared in function f1

, such as hr.pkg1.f1.n

from function f2

, raises an error. See

"Private Versus Public Items in Packages" on page 9-8.

Additional Examples of How to Specify Names With the Dot Notation

Dot notation is used for identifying record fields, object attributes, and items inside packages or other schemas. When you combine these items, you might need to use expressions with multiple levels of dots, where it is not always clear what each dot refers to. Here are some of the combinations:

Field or Attribute of a Function Return Value

func_name().field_name

func_name().attribute_name

Schema Object Owned by Another Schema

schema_name.table_name

schema_name.procedure_name() schema_name.type_name.member_name()

Packaged Object Owned by Another User

schema_name.package_name.procedure_name() schema_name.package_name.record_name.field_name

Record Containing an Object Type

record_name.field_name.attribute_name

record_name.field_name.member_name()

Differences in Name Resolution Between PL/SQL and SQL

The name resolution rules for PL/SQL and SQL are similar. You can avoid the few differences if you follow the capture avoidance rules. For compatibility, the SQL rules are more permissive than the PL/SQL rules. SQL rules, which are mostly context sensitive, recognize as legal more situations and DML statements than the PL/SQL rules.

How PL/SQL Resolves Identifier Names

B-3

Understanding Capture

■

PL/SQL uses the same name-resolution rules as SQL when the PL/SQL compiler processes a SQL statement, such as a DML statement. For example, for a name such as

HR.JOBS

, SQL matches objects in the

schema first, then packages, types, tables, and views in the current schema.

PL/SQL uses a different order to resolve names in PL/SQL statements such as assignments and procedure calls. In the case of a name

HR.JOBS

, PL/SQL searches first for packages, types, tables, and views named

in the current schema, then for objects in the

schema.

For information on SQL naming rules, see Oracle Database SQL Reference.

Understanding Capture

When a declaration or type definition in another scope prevents the compiler from resolving a reference correctly, that declaration or definition is said to capture the reference. Usually this is the result of migration or schema evolution. There are three kinds of capture: inner, same-scope, and outer. Inner and same-scope capture apply only in SQL scope.

Inner Capture

An inner capture occurs when a name in an inner scope no longer refers to an entity in an outer scope:

■

The name might now resolve to an entity in an inner scope.

■

The program might cause an error, if some part of the identifier is captured in an inner scope and the complete reference cannot be resolved.

If the reference points to a different but valid name, you might not know why the program is acting differently.

In the following example, the reference to col2

in the inner

SELECT

statement binds to column col2

in table tab1

because table tab2

has no column named col2

CREATE TABLE tab1 (col1 NUMBER, col2 NUMBER);

INSERT INTO tab1 VALUES (100, 10);

CREATE TABLE tab2 (col1 NUMBER);

INSERT INTO tab2 VALUES (100);

CREATE OR REPLACE PROCEDURE proc AS

CURSOR c1 IS SELECT * FROM tab1

WHERE EXISTS (SELECT * FROM tab2 WHERE col2 = 10);

BEGIN

NULL;

END;

In the preceding example, if you add a column named col2

to table tab2

ALTER TABLE tab2 ADD (col2 NUMBER); then procedure proc

is invalidated and recompiled automatically upon next use.

However, upon recompilation, the col2

in the inner

SELECT

statement binds to column col2

in table tab2

because tab2

is in the inner scope. Thus, the reference to col2

is captured by the addition of column col2

to table tab2

Using collections and object types can cause more inner capture situations. In the following example, the reference to hr.tab2.a

resolves to attribute a

of column

B-4

Oracle Database PL/SQL User’s Guide and Reference

Avoiding Inner Capture in DML Statements tab2

in table tab1

through table alias hr,

which is visible in the outer scope of the query:

CREATE TYPE type1 AS OBJECT (a NUMBER);

CREATE TABLE tab1 (tab2 type1);

INSERT INTO tab1 VALUES ( type1(10) );

CREATE TABLE tab2 (x NUMBER);

INSERT INTO tab2 VALUES ( 10 );

-- in the following, alias tab1 with same name as schema name, which

-- is not a good practice but is used here for illustration purpose

-- note lack of alias in second SELECT

SELECT * FROM tab1 hr

WHERE EXISTS (SELECT * FROM hr.tab2 WHERE x = hr.tab2.a);

In the preceding example, you might add a column named a

to table hr.tab2,

which appears in the inner subquery. When the query is processed, an inner capture occurs because the reference to hr.tab2.a

resolves to column a

of table tab2

in schema hr

You can avoid inner captures by following the rules given in

"Avoiding Inner Capture in DML Statements" on page B-5. According to those rules, you should revise the

query as follows:

SELECT * FROM hr.tab1 p1

WHERE EXISTS (SELECT * FROM hr.tab2 p2 WHERE p2.x = p1.tab2.a);

Same-Scope Capture

In SQL scope, a same-scope capture occurs when a column is added to one of two tables used in a join, so that the same column name exists in both tables. Previously, you could refer to that column name in a join query. To avoid an error, now you must qualify the column name with the table name.

Outer Capture

An outer capture occurs when a name in an inner scope, which once resolved to an entity in an inner scope, is resolved to an entity in an outer scope. SQL and PL/SQL are designed to prevent outer captures. You do not need to take any action to avoid this condition.

Avoiding Inner Capture in DML Statements

You can avoid inner capture in DML statements by following these rules:

■

Specify an alias for each table in the DML statement.

Keep table aliases unique throughout the DML statement.

Avoid table aliases that match schema names used in the query.

Qualify each column reference with the table alias.

Qualifying a reference with schema_name.table_name

does not prevent inner capture if the statement refers to tables with columns of a user-defined object type.

How PL/SQL Resolves Identifier Names

B-5

Qualifying References to Object Attributes and Methods

Columns of a user-defined object type allow for more inner capture situations. To minimize problems, the name-resolution algorithm includes the following rules for the use of table aliases.

References to Attributes and Methods

All references to attributes and methods must be qualified by a table alias. When referencing a table, if you reference the attributes or methods of an object stored in that table, the table name must be accompanied by an alias. As the following examples show, column-qualified references to an attribute or method are not allowed if they are prefixed with a table name:

CREATE TYPE t1 AS OBJECT (x NUMBER);

CREATE TABLE tb1 (col1 t1);

BEGIN

-- following inserts are allowed without an alias

-- because there is no column list

INSERT INTO tb1 VALUES ( t1(10) );

INSERT INTO tb1 VALUES ( t1(20) );

INSERT INTO tb1 VALUES ( t1(30) );

END;

BEGIN

UPDATE tb1 SET col1.x = 10 WHERE col1.x = 20; -- error, not allowed

END;

BEGIN

UPDATE tb1 SET tb1.col1.x = 10 WHERE tb1.col1.x = 20; -- not allowed

END;

BEGIN

UPDATE hr.tb1 SET hr.tb1.col1.x = 10 WHERE hr.tb1.col1.x = 20; -- not allowed

END;

BEGIN -- following allowed with table alias

UPDATE hr.tb1 t set t.col1.x = 10 WHERE t.col1.x = 20;

END;

DECLARE

y NUMBER;

BEGIN -- following allowed with table alias

SELECT t.col1.x INTO y FROM tb1 t WHERE t.col1.x = 30;

END;

BEGIN

DELETE FROM tb1 WHERE tb1.col1.x = 10; -- not allowed

END;

BEGIN -- following allowed with table alias

DELETE FROM tb1 t WHERE t.col1.x = 10;

END;

B-6

Oracle Database PL/SQL User’s Guide and Reference

Qualifying References to Object Attributes and Methods

References to Row Expressions

Row expressions must resolve as references to table aliases. You can pass row expressions to operators

REF

and

VALUE

, and you can use row expressions in the

SET clause of an

UPDATE

statement. Some examples follow:

CREATE TYPE t1 AS OBJECT (x number);

CREATE TABLE ot1 OF t1;

BEGIN

-- following inserts are allowed without an alias

-- because there is no column list

INSERT INTO ot1 VALUES ( t1(10) );

INSERT INTO ot1 VALUES ( 20 );

INSERT INTO ot1 VALUES ( 30 );

END;

BEGIN

UPDATE ot1 SET VALUE(ot1.x) = t1(20) WHERE VALUE(ot1.x) = t1(10); -- not allowed

END;

BEGIN -- following allowed with table alias

UPDATE ot1 o SET o = (t1(20)) WHERE o.x = 10;

END;

DECLARE

n_ref REF t1;

BEGIN -- following allowed with table alias

SELECT REF(o) INTO n_ref FROM ot1 o WHERE VALUE(o) = t1(30);

END;

DECLARE

n t1;

BEGIN -- following allowed with table alias

SELECT VALUE(o) INTO n FROM ot1 o WHERE VALUE(o) = t1(30);

END;

DECLARE

n NUMBER;

BEGIN -- following allowed with table alias

SELECT o.x INTO n FROM ot1 o WHERE o.x = 30;

END;

BEGIN

DELETE FROM ot1 WHERE VALUE(ot1) = (t1(10)); -- not allowed

END;

BEGIN -- folowing allowed with table alias

DELETE FROM ot1 o WHERE VALUE(o) = (t1(20));

END;

How PL/SQL Resolves Identifier Names

B-7

Qualifying References to Object Attributes and Methods

B-8

Oracle Database PL/SQL User’s Guide and Reference

PL/SQL Program Limits

This appendix discusses the program limits that are imposed by the PL/SQL language. PL/SQL is based on the programming language Ada. As a result, PL/SQL uses a variant of Descriptive Intermediate Attributed Notation for Ada (DIANA), a tree-structured intermediate language. It is defined using a meta-notation called

Interface Definition Language (IDL). DIANA is used internally by compilers and other tools.

At compile time, PL/SQL source code is translated into machine-readable m-code.

Both the DIANA and m-code for a procedure or package are stored in the database. At run time, they are loaded into the shared memory pool. The DIANA is used to compile dependent procedures; the m-code is simply executed.

In the shared memory pool, a package spec, object type spec, standalone subprogram, or anonymous block is limited to 67108864 (2**26) DIANA nodes which correspond to tokens such as identifiers, keywords, operators, and so on. This allows for ~6,000,000 lines of code unless you exceed limits imposed by the PL/SQL compiler, some of

which are given in Table C–1 .

Table C–1 PL/SQL Compiler Limits

Item

bind variables passed to a program unit exception handlers in a program unit fields in a record levels of block nesting levels of record nesting levels of subquery nesting levels of label nesting levels of nested collections magnitude of a

BINARY_INTEGER

value magnitude of a

PLS_INTEGER

value number of formal parameters in an explicit cursor, function, or procedure objects referenced by a program unit precision of a

FLOAT

value (binary digits) precision of a

NUMBER

value (decimal digits) precision of a

REAL

value (binary digits)

Limit

32768

65536

255

254

98 no predefined limit

-2147483648..2147483647

65536

126

PL/SQL Program Limits

C-1

Table C–1 (Cont.) PL/SQL Compiler Limits

Item

size of an identifier (characters) size of a string literal (bytes) size of a

CHAR

value (bytes) size of a

LONG

value (bytes) size of a

LONG RAW

value (bytes) size of a

RAW

value (bytes) size of a

VARCHAR2

value (bytes) size of an

NCHAR

value (bytes) size of an

NVARCHAR2

value (bytes) size of a

BFILE

value (bytes) size of a

BLOB

value (bytes) size of a

CLOB

value (bytes) size of an

NCLOB

value (bytes)

Limit

32767

32760

32767

4G * value of DB_BLOCK_SIZE parameter

To estimate how much memory a program unit requires, you can query the data dictionary view user_object_size

. The column parsed_size

returns the size (in bytes) of the "flattened" DIANA. For example:

SQL> SELECT * FROM user_object_size WHERE name = 'PKG1';

NAME TYPE SOURCE_SIZE PARSED_SIZE CODE_SIZE ERROR_SIZE

----------------------------------------------------------------

PKG1 PACKAGE 46 165 119 0

PKG1 PACKAGE BODY 82 0 139 0

Unfortunately, you cannot estimate the number of DIANA nodes from the parsed size.

Two program units with the same parsed size might require 1500 and 2000 DIANA nodes, respectively because, for example, the second unit contains more complex SQL statements.

When a PL/SQL block, subprogram, package, or object type exceeds a size limit, you get an error such as

PLS-00123: program too large

. Typically, this problem occurs with packages or anonymous blocks. With a package, the best solution is to divide it into smaller packages. With an anonymous block, the best solution is to redefine it as a group of subprograms, which can be stored in the database.

For additional information about the limits on datatypes, see

Chapter 3, "PL/SQL

Datatypes" . For limits on collection subscripts, see

Table D–2 . Reserved words can never be used as identifiers. Keywords

C-2

Oracle Database PL/SQL User’s Guide and Reference

PL/SQL Reserved Words and Keywords

The words listed in this appendix are reserved by PL/SQL. You should not use them to name program objects such as constants, variables, cursors, schema objects such as columns, tables, or indexes.

These words reserved by PL/SQL are classified as keywords or reserved words. See

Table D–1 and

can be used as identifiers, but this is not recommended.

Some of these words are also reserved by SQL. For a list of the Oracle database reserved words, see Oracle Database SQL Reference. You can generate a list of all keywords and reserved words with the

V$RESERVED_WORDS

view, described in Oracle

Database Reference.

Table D–1 lists the PL/SQL reserved words.

Table D–1 PL/SQL Reserved Words

Begins with: Reserved Words

A ALL, ALTER, AND, ANY, ARRAY, ARROW, AS, ASC, AT

BEGIN, BETWEEN, BY

CASE, CHECK, CLUSTERS, CLUSTER, COLAUTH, COLUMNS, COMPRESS, CONNECT, CRASH, CREATE,

CURRENT

DECIMAL, DECLARE, DEFAULT, DELETE, DESC, DISTINCT, DROP

ELSE, END, EXCEPTION, EXCLUSIVE, EXISTS

FETCH, FORM, FOR, FROM

GOTO, GRANT, GROUP

HAVING

IDENTIFIED, IF, IN, INDEXES, INDEX, INSERT, INTERSECT, INTO, IS

LIKE, LOCK

MINUS, MODE

NOCOMPRESS, NOT, NOWAIT, NULL

OF, ON, OPTION, OR, ORDER,OVERLAPS

PRIOR, PROCEDURE, PUBLIC

RANGE, RECORD, RESOURCE, REVOKE

SELECT, SHARE, SIZE, SQL, START, SUBTYPE

TABAUTH, TABLE, THEN, TO, TYPE

UNION, UNIQUE, UPDATE, USE

VALUES, VIEW, VIEWS

WHEN, WHERE, WITH

PL/SQL Reserved Words and Keywords

D-1

Table D–2 lists the PL/SQL keywords.

Table D–2 PL/SQL Keywords

Begins with: Keywords

A, ADD, AGENT, AGGREGATE, ARRAY, ATTRIBUTE, AUTHID, AVG

BFILE_BASE, BINARY, BLOB_BASE, BLOCK, BODY, BOTH, BOUND, BULK, BYTE

C, CALL, CALLING, CASCADE, CHAR, CHAR_BASE, CHARACTER, CHARSETFORM, CHARSETID,

CHARSET, CLOB_BASE, CLOSE, COLLECT, COMMENT, COMMIT, COMMITTED, COMPILED,

CONSTANT, CONSTRUCTOR, CONTEXT, CONVERT, COUNT, CURSOR, CUSTOMDATUM

DANGLING, DATA, DATE, DATE_BASE, DAY, DEFINE, DETERMINISTIC, DOUBLE, DURATION

ELEMENT, ELSIF, EMPTY, ESCAPE, EXCEPT, EXCEPTIONS, EXECUTE, EXIT, EXTERNAL

FINAL, FIXED, FLOAT, FORALL, FORCE, FUNCTION

GENERAL

HASH, HEAP, HIDDEN, HOUR

IMMEDIATE, INCLUDING, INDICATOR, INDICES, INFINITE, INSTANTIABLE, INT, INTERFACE,

INTERVAL, INVALIDATE, ISOLATION

JAVA

LANGUAGE, LARGE, LEADING, LENGTH, LEVEL, LIBRARY, LIKE2, LIKE4, LIKEC, LIMIT, LIMITED,

LOCAL, LONG, LOOP

MAP, MAX, MAXLEN, MEMBER, MERGE, MIN, MINUTE, MOD, MODIFY, MONTH, MULTISET

NAME, NAN, NATIONAL, NATIVE, NCHAR, NEW, NOCOPY, NUMBER_BASE

OBJECT, OCICOLL, OCIDATETIME, OCIDATE, OCIDURATION, OCIINTERVAL, OCILOBLOCATOR,

OCINUMBER, OCIRAW, OCIREFCURSOR, OCIREF, OCIROWID, OCISTRING, OCITYPE, ONLY, OPAQUE,

OPEN, OPERATOR, ORACLE, ORADATA, ORGANIZATION, ORLANY, ORLVARY, OTHERS, OUT,

OVERRIDING

PACKAGE, PARALLEL_ENABLE, PARAMETER, PARAMETERS, PARTITION, PASCAL, PIPE, PIPELINED,

PRAGMA, PRECISION, PRIVATE

RAISE, RANGE, RAW, READ, RECORD, REF, REFERENCE, REM, REMAINDER, RENAME, RESULT,

RETURN, RETURNING, REVERSE, ROLLBACK, ROW

SAMPLE, SAVE, SAVEPOINT, SB1, SB2, SB4, SECOND, SEGMENT, SELF, SEPARATE, SEQUENCE,

SERIALIZABLE, SET, SHORT, SIZE_T, SOME, SPARSE, SQLCODE, SQLDATA, SQLNAME, SQLSTATE,

STANDARD, STATIC, STDDEV, STORED, STRING, STRUCT, STYLE, SUBMULTISET, SUBPARTITION,

SUBSTITUTABLE, SUBTYPE, SUM, SYNONYM

TDO, THE, TIME, TIMESTAMP, TIMEZONE_ABBR, TIMEZONE_HOUR, TIMEZONE_MINUTE,

TIMEZONE_REGION, TRAILING, TRANSAC, TRANSACTIONAL, TRUSTED, TYPE

UB1, UB2, UB4, UNDER, UNSIGNED, UNTRUSTED, USE, USING

VALIST, VALUE, VARIABLE, VARIANCE, VARRAY, VARYING, VOID

WHILE, WORK, WRAPPED, WRITE

YEAR

ZONE

D-2

Oracle Database PL/SQL User’s Guide and Reference

Index

Symbols

%BULK_EXCEPTIONS. See BULK_EXCEPTIONS cursor attribute

%BULK_ROWCOUNT. See BULK_ROWCOUNT cursor attribute

%FOUND. See FOUND cursor attribute

%ISOPEN. See ISOPEN cursor attribute

%NOTFOUND. See NOTFOUND cursor attribute

%ROWCOUNT. See ROWCOUNT cursor attribute

%ROWTYPE. See ROWTYPE attribute

%TYPE. See TYPE attribute

:= assignment operator, 1-6

|| concatenation operator, 2-23

. item separator, 2-2

<< label delimiter, 2-2

.. range operator, 2-2, 4-9

=, !=, <>, and ~= relational operators, 2-22

<, >, <=, and >= relational operators, 2-22

@ remote access indicator, 2-2, 2-13

-- single-line comment delimiter, 2-2

; statement terminator, 2-2, 13-12

- subtraction/negation operator, 2-2

A

ACCESS_INTO_NULL exception, 10-4

actual parameters, 6-19

additional information

Oracle Technology Network, xxii, 1-1

address

REF CURSOR, 6-20

advantages

PL/SQL, 1-1

aggregate assignment, 2-12

aggregate functions

and PL/SQL, 6-3

AVG, 2-39

COUNT, 2-39

AL16UTF16 character encoding, 3-9

aliases

using with a select list, 2-12

aliasing

for expression values in a cursor FOR loop, 6-17

parameters, 8-24

ALL row operator, 6-3, 6-6

ALL_PLSQL_OBJECT_SETTINGS view

PL/SQL compiler parameter settings, 11-2, 11-28

ALTER .. COMPILE statement, 10-18

ALTER PROCEDURE

using to recompile a procedure, 10-19

analytic functions

CORR, 2-39

LAG, 2-39

anonymous blocks, 1-4

apostrophes, 2-6

architecture

PL/SQL, 1-18

ARRAY

VARYING, 5-6

arrays

associative, 5-2 index-by-tables, 5-2 variable-size, 5-2

articles

technical on OTN, xxii

defining a procedure, 8-3 defining a procedure body, 8-3

assignment operator, 1-6

assignment statement

links to examples, 13-5

syntax, 13-3

assignments

aggregate, 2-12

character string, 3-23

collection, 5-12

field, 5-32

IN OUT parameters, 1-6

records, 5-32

semantics, 3-23

variables, 1-6

associative arrays

sets of key-value pairs, 5-3

syntax, 13-17

VARCHAR2 keys and globalization settings, 5-4

versus nested tables, 5-5

asynchronous operations, 9-9

atomically null

object types in PL/SQL, 12-3

attributes

Index-1

%ROWTYPE, 1-9, 2-11

%TYPE, 1-8, 2-10

explicit cursors, 6-12

AUTHID clause

specifying privileges for a subprogram, 8-16

use with functions, 8-4

using to specify privileges of invoker, 8-15

autonomous functions

calling from SQL, 6-42

RESTRICT_REFERENCES pragma, 6-42

autonomous transactions

advantages, 6-37

avoiding errors, 6-40

comparison with nested transactions, 6-39 controlling, 6-39

in PL/SQL, 6-37

SQL%ROWCOUNT attribute, 6-8

autonomous triggers

using, 6-41

AUTONOMOUS_TRANSACTION pragma

defining, 6-37

links to examples, 13-7

syntax, 13-6

AVG

SQL aggregate function, 2-39

B

base types

PL/SQL number types, 3-2

PL/SQL types, 3-17

basic loops, 4-7

BEGIN

block structure, 1-5

start of executable part, 8-3

start of executable PL/SQL block, 13-10 syntax, 13-10

best practices

locating information on OTN, xxii

Oracle Technology Network, 1-1, 11-1

BETWEEN clause

FORALL, 13-56

BETWEEN comparison operator, 2-23

expressions, 13-48

BFILE datatype, 3-11

binary operators, 2-19

BINARY_DOUBLE datatype, 3-2

BINARY_FLOAT and BINARY_DOUBLE datatypes

for computation-intensive programs, 11-20

BINARY_FLOAT datatype, 3-2

BINARY_FLOAT_INFINITY

BINARY_FLOAT_MAX_NORMAL

BINARY_FLOAT_MAX_SUBNORMAL

BINARY_FLOAT_MIN_NORMAL

BINARY_FLOAT_MIN_SUBNORMAL

Index-2

BINARY_FLOAT_NAN

BINARY_INTEGER datatype, 3-2

compared to PLS_INTEGER, xxvii new features, xxvii

BINARY_INTEGER. See also PLS_INTEGER

bind variables, 1-7

binding, 11-8

blank-padding semantics, 3-24

block declaration

blocks

links to examples, 13-12

BODY

CREATE PACKAGE SQL statement, 1-14, 9-1,

13-85

CREATE TYPE SQL statement, 13-78

with SQL CREATE PACKAGE statement, 1-14,

body

procedure, 8-3, 13-87

Boolean

assigning values, 2-19

expressions, 2-24

literals, 2-7

BOOLEAN datatype, 3-12

built-in functions, 2-38

bulk

fetches, 11-17

returns, 11-18

BULK clause

with COLLECT, 11-15

BULK COLLECT clause, 11-15

checking whether no results are returned, 11-16

DELETE statement, 13-36

EXECUTE IMMEDIATE, 13-41

FETCH, 13-53

retrieving DML results, 11-18

retrieving query results with, 11-15

RETURNING clause, 13-101

returning multiple rows, 6-15

SELECT INTO, 13-108

using LIMIT clause, 11-16, 11-18 using ROWNUM pseudocolumn, 11-16 using SAMPLE clause, 11-16

using with FORALL statement, 11-19

bulk SQL

in dynamic SQL, 7-5

using to reduce loop overhead, 11-8

BULK_EXCEPTIONS cursor attribute

ERROR_CODE field, 11-14

ERROR_INDEX field, 11-14

example, 11-15

handling FORALL exceptions, 11-14 using ERROR_CODE field with SQLERRM, 11-14

BULK_ROWCOUNT cursor attribute

affected by FORALL, 11-12

by-reference parameter passing, 8-24 by-value parameter passing, 8-24

C

CALL

SQL statement, 1-15

call specification, 9-2

calling

Java stored procedures, 8-22

procedures, 1-14

stored subprograms, 1-20

calls

inter-language, 8-22

resolving subprogram, 8-12

subprograms, 8-7

CARDINALITY operator

for nested tables, 5-16

carriage returns, 2-2

CASE expressions, 2-26

overview, 1-10

case sensitivity

identifier, 2-3

string literal, 2-6

CASE statement

links to examples, 13-15

searched, 4-5

syntax, 13-14

using, 4-4

CASE_NOT_FOUND exception, 10-4

CHAR datatype, 3-4

differences with VARCHAR2, 3-23

character literals, 2-6

character sets

PL/SQL, 2-1

CHARACTER subtype, 3-5

character values

clauses

AUTHID, 8-4, 8-15, 8-16

BULK COLLECT, 11-15

LIMIT, 11-18

CLOB datatype, 3-11

CLOSE statement

disables cursor, 6-12

disabling cursor variable

closing, 6-26

links to examples, 13-16 syntax, 13-16

code samples

Oracle Technology Network, xxii, 1-1

collating sequence, 2-24

COLLECT clause

with BULK, 11-15

collection exceptions

when raised, 5-28

collection methods

syntax, 13-20

usage, 5-19

COLLECTION_IS_NULL exception, 10-4

collections

allowed subscript ranges, 5-11

applying methods to parameters, 5-26

assigning, 5-12

associative arrays versus nested tables, 5-5

avoiding exceptions, 5-27

bulk binding, 5-36, 11-8

choosing the type to use, 5-5

comparing, 5-16

constructors, 5-10

COUNT method, 5-20

declaring variables, 5-6, 5-7

links to examples, 13-19, 13-22

methods, 5-19

multilevel, 5-18

NEXT method, 5-22

operators to transform nested tables, 5-13

ordered group of elements, 5-1

overview, 1-16

PRIOR method, 5-22

referencing, 5-10

referencing elements, 5-11

scope, 5-6

syntax, 13-17

testing for null, 5-16

TRIM method, 5-24

types in PL/SQL, 5-1

using object types with, 12-9

varrays versus nested tables, 5-5

column aliases

expression values in a cursor loop, 6-17

when needed, 2-12

COMMENT clause

using with transactions, 6-30

comments

Index-3

in PL/SQL, 2-7

links to examples, 13-23

restrictions, 2-8

syntax, 13-23

COMMIT statement, 6-30, 13-24

links to examples, 13-24

comparison operators, 6-6

comparisons

of character values, 3-24

of expressions, 2-24

of null collections, 5-16

operators, 2-22

PL/SQL, 2-19

with NULLs, 2-27

compiler parameter settings

ALL_PLSQL_OBJECT_SETTINGS view, 11-2,

11-28

compiler parameters

and REUSE SETTINGS clause, 11-2

PL/SQL, 11-1

compiling

conditional, 1-12, 2-30

PL/SQL procedures for native execution, 11-22

composite types

collection and records, 5-1

overview, 3-1

concatenation operator, 2-23

treatment of nulls, 2-29

conditional compilation, 1-12, 2-30

availability for previous Oracle database releases, 2-31 control tokens, 2-31

examples, 2-35

inquiry directives, 2-31

limitations, 2-37

NLS_LENGTH_SEMANTICS initialization parameter, 2-32

PLSQL_CCFLAGS initialization parameter, 2-32

PLSQL_CODE_TYPE initialization parameter, 2-32

PLSQL_DEBUG initialization parameter, 2-32

PLSQL_LINE flag, 2-32

PLSQL_OPTIMIZE_LEVEL initialization parameter, 2-32

PLSQL_UNIT flag, 2-33

PLSQL_WARNINGS initialization parameter, 2-32

restrictions, 2-37

static constants, 2-33

using PLSQL_CCFLAGS initialization parameter, 2-34

using static expressions with, 2-33

using with DBMS_DB_VERSION, 2-35

using with DBMS_PREPROCESSOR, 2-36

conditional control, 4-2

conditional statement

guidelines, 4-6

CONSTANT

declaration, 13-26

Index-4

for declaring constants, 1-7, 2-9

constants

declaring, 1-7, 2-8, 2-9

links to examples, 13-27

static, 2-33

syntax, 13-25

understanding PL/SQL, 1-5

constraints

constructors

context

control structures

overview of PL/SQL, 4-1

conventions

conversions

CORR

SQL analytic function, 2-39

correlated subqueries, 6-18

COUNT

SQL aggregate function, 2-39

COUNT method

collections, 5-20, 13-20

CREATE

with PROCEDURE statement, 1-13, 1-19, 8-2

CREATE FUNCTION statement, 1-13, 1-19, 8-2

CREATE PROCEDURE statement, 1-13, 1-19, 8-2

CREATE statement

packages, 1-14, 9-1

with FUNCTION, 1-13, 1-19, 8-2

CREATE_WRAPPED function

obfuscation, A-4 using, A-4

creating

functions, 1-13, 1-19, 8-2

packages, 1-14, 9-1

procedures, 1-13, 1-19, 8-2

CURRENT OF clause

with UPDATE, 6-35

CURRVAL

pseudocolumn, 6-4

cursor attributes

%BULK_EXCEPTIONS, 11-14

%BULK_ROWCOUNT, 11-12

links to examples, 13-29

syntax, 13-28

values after OPEN, FETCH, and CLOSE, 6-14

cursor declarations

links to examples, 13-35

syntax, 13-33

cursor expressions

examples, 6-29

REF CURSORs, 6-29

restrictions, 6-28 using, 6-28

cursor FOR loops

passing parameters to, 6-19

cursor subqueries

using, 6-28

cursor variables, 6-20 advantages of, 6-20

as parameters to table functions, 11-36

avoiding errors with, 6-27

links to examples, 13-32

opening, 6-22 passing as parameters, 6-22

reducing network traffic, 6-26

restrictions, 6-27

syntax, 13-30

using as a host variable, 6-24

CURSOR_ALREADY_OPEN exception, 10-4

cursors

advantages of using cursor variables, 6-20

attributes of explicit, 6-12

attributes of implicit, 6-7

closing explicit, 6-12

declaring explicit, 6-8

definition, 1-16 explicit, 1-16, 6-8

explicit FOR loops, 6-16

expressions, 6-28

fetching from, 6-9

guidelines for implicit, 6-8

implicit, 1-16

opening explicit, 6-9

packaged, 9-11

parameterized, 6-19

REF CURSOR variables, 6-20

RETURN clause, 9-11

scope rules for explicit, 6-9

SYS_REFCURSOR type, 11-36

variables, 6-20

D

data abstraction

understanding PL/SQL, 1-16

database character set, 3-9

database triggers, 1-20

datatypes

explicit conversion, 3-21

families, 3-1

implicit conversion, 3-21

INTERVAL DAY TO SECOND, 3-16

INTERVAL YEAR TO MONTH, 3-16

LONG, 3-5

LONG RAW, 3-6

national character, 3-9

scalar versus composite, 3-1

TABLE, 5-6

TIMESTAMP, 3-13

TIMESTAMP WITH LOCAL TIME ZONE, 3-15

TIMESTAMP WITH TIME ZONE, 3-14

dates

TO_CHAR default format, 3-23

datetime

DAY

DBMS_ALERT package, 9-9

DBMS_DB_VERSION package

using with conditional compilation, 2-35

DBMS_DDL package

functions for hiding PL/SQL source code, A-1

obfuscating PL/SQL code, A-1

using, A-4 wrap functions, A-4

wrapping PL/SQL code, A-1

DBMS_OUTPUT package

displaying output, 1-15

displaying output from PL/SQL, 9-9

using PUT_LINE to display output, 1-6

DBMS_PIPE package, 9-10

DBMS_PREPROCESSOR package

using with conditional compilation, 2-36

DBMS_PROFILE package

Index-5

gathering statistics for tuning, 11-7

DBMS_SQL package, 7-2

PARSE procedure, 8-17

replace with dynamic SQL, 7-2

upgrade to dynamic SQL, 11-20

using for a query, 7-1

DBMS_TRACE package

tracing code for tuning, 11-8

DBMS_WARNING package

controlling warning messages in PL/SQL, 10-19

dbmsupbin.sql script

interpreted compilation, 11-29

dbmsupgnv.sql script

for PL/SQL native compilation, 11-31

deadlocks

how handled by PL/SQL, 6-33

DEC

DECIMAL

declarations

cursor variables, 6-21

exceptions in PL/SQL, 10-6

explicit cursor, 6-8

object in a PL/SQL block, 12-2

PL/SQL functions, 1-8

PL/SQL procedures, 1-8

PL/SQL subprograms, 1-8

PL/SQL variables, 1-8

restrictions, 2-13

subprograms, 8-5

using %ROWTYPE, 2-11

using %TYPE attribute, 2-10

using DEFAULT, 2-9 using NOT NULL constraint, 2-9

declarative part

DECLARE

for local declarations, 8-3

start of declarative part of a PL/SQL block, 13-11 syntax, 13-11

DECODE function

treatment of nulls, 2-29

DEFAULT keyword

for assignments, 2-9

DEFAULT option

FUNCTION, 13-62

RESTRICT_REFERENCES, 13-98

default parameter values, 8-9

default value

effect on %ROWTYPE declaration, 2-11

effect on %TYPE declaration, 2-10

DEFINE

limitations of use with wrap utility, A-2

Index-6

definer's rights

privileges on subprograms, 8-15

DELETE method

collections, 5-25, 13-21

DELETE statement

links to examples, 13-37

syntax, 13-36

delimiters, 2-2

demos

PL/SQL, xxi

dense collections

arrays versus nested tables, 5-2

DETERMINISTIC hint

function syntax, 13-60

use with functions, 8-4

digits of precision, 3-3

displaying output

from PL/SQL, 1-6

setting SERVEROUTPUT, 1-15, 9-9

using DBMS_OUTPUT.PUT_LINE, 1-6

with DBMS_OUTPUT, 1-15

DISTINCT row operator, 6-3, 6-6

dot notation, 1-8

for collection methods, 5-19

for global variables, 4-12

for object attributes in PL/SQL, 12-4

for object methods in PL/SQL, 12-5

for package contents, 9-4

DOUBLE PRECISION

DUP_VAL_ON_INDEX exception, 10-4

dynamic dispatch, 8-15

dynamic SQL, 1-2, 7-1

building a dynamic multi-row query, 7-7 guidelines, 7-7

improving performance, 7-8

passing nulls, 7-10

passing object names as parameters, 7-8

RETURNING clause, 7-2

specifying parameter modes, 7-4

using cursor attributes, 7-9

using database links, 7-10

using duplicate placeholders, 7-9

using EXECUTE IMMEDIATE statement, 7-2

using invoker rights, 7-11 using RESTRICT_REFERENCES, 7-11

using the semicolon, 7-7

dynamic string length

with OPEN FOR statement, 13-83

dynamic wrapping

DBMS_DDL package, A-1

end of a PL/SQL block, 13-11

E

element types

ELSE clause

ELSIF clause

END

end of executable part, 8-3

syntax, 13-11

END IF

end of IF statement, 4-2

END LOOP

end of LOOP statement, 4-9

error handling

in PL/SQL, 10-1

overview, 1-18

error messages

maximum length, 10-14

ERROR_CODE

BULK_EXCEPTIONS cursor attribute field, 11-14 using with SQLERRM, 11-14

ERROR_INDEX

BULK_EXCEPTIONS cursor attribute field, 11-14

evaluation

short-circuit, 2-21

EXCEPTION

block structure, 1-5

exception handling part, 8-3

exception-handling part of a block, 13-11 syntax in PL/SQL block, 13-11

exception definition

syntax, 13-39

exception handlers

OTHERS handler, 10-2

overview, 1-18

using RAISE statement in, 10-11, 10-12

using SQLCODE function in, 10-14 using SQLERRM function in, 10-14

WHEN clause, 10-12

EXCEPTION_INIT pragma

links to examples, 13-38 syntax, 13-38

using with RAISE_APPLICATION_ERROR, 10-8

with exceptions, 10-7

exception-handling part

of function, 8-4

of PL/SQL block, 1-5

of procedure, 8-3

exceptions

advantages of PL/SQL, 10-3

branching with GOTO, 10-13

catching unhandled in PL/SQL, 10-15 continuing after an exception is raised, 10-15

controlling warning messages, 10-18

declaring in PL/SQL, 10-6

definition, 13-39

handling in PL/SQL, 10-1

links to examples, 13-40

list of predefined in PL/SQL, 10-4

locator variables to identify exception locations, 10-17

OTHERS handler in PL/SQL, 10-12

PL/SQL compile-time warnings, 10-17

PL/SQL error condition, 10-1

PL/SQL warning messages, 10-17

predefined in PL/SQL, 10-4

propagation in PL/SQL, 10-9

raise_application_error procedure, 10-7

raised in a PL/SQL declaration, 10-13 raised in handlers, 10-13

raising in PL/SQL, 10-9 raising predefined explicitly, 10-9 raising with RAISE statement, 10-9

redeclaring predefined in PL/SQL, 10-8

reraising in PL/SQL, 10-11

retrying a transaction after, 10-16

scope rules in PL/SQL, 10-6

tips for handling PL/SQL errors, 10-15

user-defined in PL/SQL, 10-5

using EXCEPTION_INIT pragma, 10-7

using SQLCODE, 10-14 using SQLERRM, 10-14

using the DBMS_WARNING package, 10-19

using WHEN and OR, 10-12

executable part

EXECUTE IMMEDIATE statement, 7-2

links to examples, 13-43

syntax, 13-41

EXECUTE privilege

subprograms, 8-18

EXISTS method

collections, 5-19, 13-21

EXIT statement

early exit of LOOP, 4-12

links to examples, 13-44

stopping a loop, 4-7

syntax, 13-44

using, 4-7 where allowed, 4-7

EXIT-WHEN statement

overview, 1-11

using, 4-8

explicit cursors, 6-8

explicit datatype conversion, 3-21

explicit declarations

cursor FOR loop record, 6-16

expressions

EXTEND method

collections, 5-23, 13-21

Index-7

extended rowids, 3-7

external

references, 8-16

routines, 8-22 subprograms, 8-22

F

FALSE value, 2-7

features, new, xxv

FETCH statement

links to examples, 13-55

syntax, 13-53

using explicit cursors, 6-9

with cursor variable, 6-25

fetching

fields

FIRST method

collections, 5-21, 13-21

FLOAT

using, 11-9 using to improve performance, 11-9

FOR loops

explicit cursors, 6-16

nested, 4-12

FOR UPDATE clause, 6-9

when to use, 6-34

FORALL statement

links to examples, 13-58

syntax, 13-56

using with BULK COLLECT clause, 11-19

with rollbacks, 11-12

FOR-LOOP statement

syntax, 13-73

using, 4-9

formal parameters, 6-19

format

masks, 3-23

forward

declarations of subprograms, 8-5

references, 2-13

FOUND cursor attribute

explicit, 6-12

with CREATE statement, 1-13, 1-19, 8-2

FUNCTION

function declaration

functions

creating, 1-13, 1-19, 8-2

declaration, 13-59

DETERMINISTIC hint, 8-4

Index-8

in PL/SQL, 8-1

links to examples, 13-62

PARALLEL_ENABLE option, 8-4 parameters, 8-4 parts, 8-4

pipelined, 11-31

RETURN clause, 8-4

RETURN statement, 8-5

specification, 8-4

table, 11-32

understanding, 8-4

G

GOTO statement

branching into or out of exception handler, 10-13

label, 4-13

links to examples, 13-63

H

handlers

exception in PL/SQL, 10-2

handling errors

PL/SQL, 10-1

handling exceptions

PL/SQL, 10-1

raised in as PL/SQL declaration, 10-13 raised in handler, 10-13

using OTHERS handler, 10-12

handling of nulls, 2-27

hash tables

simulating with associative arrays, 5-5

hiding PL/SQL code, A-1

host arrays

bulk binds, 11-19

HOUR

datatype field, 3-12

HTF package, 9-10

HTP package, 9-10 hypertext markup language (HTML), 9-10

hypertext transfer protocol (HTTP), 1-4

UTL_HTTP package, 9-10

I

identifiers

forming, 2-3

maximum length, 2-4 quoted, 2-4

scope rules, 2-15

IF statement, 4-2

ELSE clause, 4-2

links to examples, 13-65

syntax, 13-64

using, 4-2

IF-THEN statement

using, 4-2

IF-THEN-ELSE statement

overview, 1-10

using, 4-2

IF-THEN-ELSEIF statement

using, 4-3

IMMEDIATE

with EXECUTE statement, 7-2

implicit cursors

attributes, 6-7

guidelines, 6-8

implicit datatype conversion, 3-21

implicit datatype conversions

performance, 11-5

implicit declarations

FOR loop counter, 4-11

IN comparison operator, 2-23

IN OUT parameter mode

subprograms, 8-8

IN parameter mode

subprograms, 8-7

INDEX BY

collection definition, 13-18

index-by tables

See associative arrays

INDICES OF clause

FORALL, 13-56

with FORALL, 11-9

infinite loops, 4-7

inheritance

and overloading, 8-14

initialization

collections, 5-10

objects in PL/SQL, 12-3

package, 9-6

using DEFAULT, 2-9

variable, 2-18

with NOT NULL constraint, 2-9

initialization parameters

PL/SQL compilation, 11-1

INSERT statement

links to examples, 13-67

syntax, 13-66

with a record variable, 5-33

INT

INTEGER

integer

inter-language calls, 8-22

interpreted compilation

dbmsupbin.sql script, 11-29 recompiling all PL/SQL modules, 11-29

INTERSECT set operator, 6-6

interval

arithmetic, 3-17

INTERVAL DAY TO SECOND datatype, 3-16

INTERVAL YEAR TO MONTH datatype, 3-16

intervals

datatypes, 3-12

INTO

SELECT INTO statement, 13-107

INTO clause

with FETCH statement, 6-26

INTO list

using with explicit cursors, 6-10

INVALID_CURSOR exception, 10-4

INVALID_NUMBER exception, 10-4

invoker's rights

advantages, 8-16

privileges on subprograms, 8-15

defining a procedure, 8-3 defining a procedure body, 8-3

IS A SET operator, 5-16

IS EMPTY operator, 5-16

IS NULL comparison operator, 2-23

expressions, 13-50

ISOLATION LEVEL parameter

READ COMMITTED, 13-113

SERIALIZABLE, 13-113 setting transactions, 13-113

ISOPEN cursor attribute

explicit, 6-12

use for calling external subprograms, 8-22

J

JAVA

Java

call specs, 8-23

Java stored procedures

calling from PL/SQL, 8-22

JDeveloper with PL/SQL

Oracle By Example tutorial, xxv

K

keywords

in PL/SQL, D-1

list of PL/SQL, D-2

use in PL/SQL, 2-4

L

labels

block, 2-16

block structure, 13-12

LAG

SQL analytic function, 2-39

LANGUAGE

use for calling external subprograms, 8-22

language elements

Index-9

of PL/SQL, 13-1

large object (LOB) datatypes, 3-10

LAST method

collections, 5-21, 13-21

LEVEL

with ISOLATION to set transactions, 13-113

LEVEL parameter

lexical units

PL/SQL, 2-1

LIKE comparison operator, 2-23

expressions, 13-50

LIMIT clause

FETCH, 13-54

using to limit rows for a Bulk FETCH operation, 11-18

LIMIT method

collections, 5-20, 13-21

limitations

DBMS_DDL package, A-2

native compilation, 11-25

of PL/SQL programs, C-1

PL/SQL compiler, C-1

wrap utility, A-2

limits

on PL/SQL programs, C-1

literals

NUMBER datatype, 2-5 numeric, 2-5 numeric datatypes, 2-5

string, 2-6

syntax, 13-68

types of PL/SQL, 2-4

LOB (large object) datatypes, 3-10

lob locators, 3-11

local subprograms, 1-19

locator variables

used with exceptions, 10-17

LOCK TABLE statement

examples, 13-71

locking a table, 6-35

syntax, 13-71

locks

modes, 6-30

overriding, 6-34

transaction processing, 6-30

using FOR UPDATE clause, 6-34

logical operators, 2-20

logical rowids, 3-6

LOGIN_DENIED exception, 10-5

LONG datatype, 3-5 maximum length, 3-5

restrictions, 3-6

supported only for backward compatibility, 3-5

LONG RAW datatype, 3-6

Index-10

converting, 3-23

maximum length, 3-6

supported only for backward compatibility, 3-5

LOOP statement

links to examples, 13-75

loops

exiting using labels, 4-8

implicit declaration of counter, 4-11

iteration, 4-10

labels, 4-8

reversing the counter, 4-10

scope of counter, 4-11

M

maximum precision, 3-3

maximum size

NVARCHAR2 value, 3-10

Oracle error message, 10-14

RAW value, 3-6

VARCHAR2 value, 3-8

MEMBER OF operator, 5-16

membership test, 2-23

memory

avoid excessive overhead, 11-6

MERGE statement

syntax, 13-76

methods

collection, 5-19

MINUS set operator, 6-6

MINUTE

MONTH

multilevel collections

using, 5-18

multi-line comments, 2-8

MULTISET EXCEPT operator, 5-13

MULTISET INTERSECT operator, 5-13

MULTISET UNION operator, 5-13

N

NAME

for calling external subprograms, 8-22

NAME parameter

setting transactions, 13-114

transactions, 6-34

name resolution, 2-14

differences between PL/SQL and SQL, B-3

global and local variables, B-1

inner capture in DML statements, B-5

overriding in subprograms, 8-17

qualified names and dot notation, B-2

qualifying references to attributes and methods, B-6

understanding, B-1

understanding capture, B-4

names

naming conventions

national character datatypes, 3-9 national character set, 3-9

National Language Support (NLS), 3-9

native compilation

and Real Application Clusters, 11-25

certified compilers in installation guides, 11-23

creating databases for, 11-29

dbmsupgnv.sql script, 11-31

dependencies, 11-24

enhancements, xxvi

how it works, 11-24

initialization parameters, 11-25

invalidation, 11-24

limitations, 11-25

modifying databases for, 11-29

new and updated components, xxvi

Oracle Metalink, 11-23

Oracle Technology Network, 11-23 performance gains, 11-23

PL/SQL code, 11-22

plsql_code_type column, 11-28

prerequirements, 11-23

revalidation, 11-24

setting up, 11-27

setting up databases, 11-28

setting up library subdirectories, 11-27

shared libraries, 11-24

spnc_commands file, 11-25

testing, 11-23 understanding, 11-23

using, 11-27

utlirp.sql script, 11-28

utlrp.sql script, 11-31

native dynamic SQL. See dynamic SQL

native execution

compiling PL/SQL procedures for, 11-22

NATURAL

NATURAL and NATURALN subtypes, 3-2

NATURALN

manipulating in PL/SQL, 12-9

NCHAR datatype, 3-9

NCLOB datatype, 3-12

nested collections, 5-18

nested cursors

using, 6-28

nested tables

sets of values, 5-2

syntax, 13-17

transforming with operators, 5-13

versus associative arrays, 5-5 versus varrays, 5-5

nesting

PL/SQL information on Oracle Technology

Network, xxv

NEXT method

collections, 5-22, 13-21

NEXTVAL

pseudocolumn, 6-4

nibble

half a byte, 3-23

NLS (National Language Support), 3-9

NLS_LENGTH_SEMANTICS initialization parameter

NO_DATA_FOUND exception, 10-5

NO COPY hint

FUNCTION, 13-61

NOCOPY compiler hint

for tuning, 11-21

restrictions on, 11-22

non-blank-padding semantics, 3-24

NOT logical operator

treatment of nulls, 2-28

NOT NULL

declaration, 13-26

NOT NULL constraint

effect on %ROWTYPE declaration, 2-11

effect on %TYPE declaration, 2-10

restriction on explicit cursors, 6-9

using in collection declaration, 5-9

using in variable declaration, 2-9

NOT NULL option

record definition, 13-95

NOT_LOGGED_ON exception, 10-5

notation

positional versus named, 8-7

NOTFOUND cursor attribute

explicit, 6-13

using with FOR UPDATE, 6-34

NOWAIT option

LOCK TABLE, 13-71

NOWAIT parameter

NVARCHAR2 datatype, 3-10

NVL function

Index-11

treatment of nulls, 2-29

null handling, 2-27

in dynamic SQL, 7-10

NULL statement

links to examples, 13-77 syntax, 13-77

using, 4-15

using in a procedure, 8-3

NUMBER datatype, 3-3

range of literals, 2-5

range of values, 3-3

NUMBER subtypes, 3-4

NUMERIC

PL/SQL code, A-1 understanding, A-1

numeric literals, 2-5

PL/SQL datatypes, 2-5

O

obfuscating

obfuscation

CREATE_WRAPPED function, A-4

DBMS_DDL package, A-4

hiding PL/SQL code, A-1

recommendations, A-1 tips, A-1 understanding, A-1

using DBMS_DDL CREATE_WRAPPED function, A-4

viewing source, A-1, A-5

WRAP function, A-4

wrap utility, A-2

object constructors

calling in PL/SQL, 12-4 passing parameters to in PL/SQL, 12-4

object methods

calling in PL/SQL, 12-5

object type declaration

syntax, 13-78

object types

declaring in a PL/SQL block, 12-2

defining in PL/SQL, 12-1

initializing in PL/SQL, 12-1, 12-3

overview, 1-17

using with invoker’s rights subprograms, 8-20

using with PL/SQL, 12-1

using with PL/SQL collections, 12-9

object-oriented programming

with PL/SQL, 12-1

ONLY parameter

with READ to set transactions, 13-113

on-the-fly wrapping

DBMS_DDL package, A-1

dynamic string length, 13-83

OPEN FOR statement

OPEN statement

Index-12

explicit cursors, 6-9

links to examples, 13-81

syntax, 13-80

OPEN-FOR statement, 6-22

links to examples, 13-84

syntax, 13-82

OPEN-FOR-USING statement

syntax, 13-82

operators

comparison, 2-22

logical, 2-20 precedence, 2-20

relational, 2-22

optimizing

PL/SQL programs, 11-2

OR keyword

using with EXCEPTION, 10-12

Oracle By Example

PL/SQL new features, xxv

Oracle Metalink

native compilation, 11-23

spnc_commands, 11-25

Oracle Technology Network

best practices, 1-1, 11-1

code samples, xxii, 1-1

information on PL/SQL new features, xxv

native compilation, 11-23

SQL injection, 7-7, 13-43

table function examples, 11-32 table functions, 11-32

tuning information, 11-1

order of evaluation, 2-20, 2-21

OTHERS clause

exception handling, 13-39

OTHERS exception handler, 10-2, 10-12

OTN

technical articles, xxii

OUT parameter mode

subprograms, 8-8

overloading

and inheritance, 8-14

guidelines, 8-10

packaged subprograms, 9-8

restrictions, 8-11

subprogram names, 8-10

P

PACKAGE

with SQL CREATE statement, 1-14, 9-1

PACKAGE BODY

with SQL CREATE statement, 1-14, 9-1

package declaration

syntax, 13-85

packaged cursors, 9-11

packaged subprograms, 1-19

packages

advantages, 9-3

bodiless, 9-4

body, 9-1, 9-5, 13-88

call specification, 9-2

calling subprograms, 9-5

contents of, 9-2

creating, 1-14, 9-1

cursor specifications, 9-11 cursors, 9-11

declaration, 13-85

dot notation, 9-4

examples of features, 9-6

global variables, 9-8

guidelines for writing, 9-10

hidden declarations, 9-1

initializing, 9-6

links to examples, 13-89

modularity, 9-3

overloading subprograms, 9-8

overview, 1-13

overview of Oracle supplied, 9-9

private versus public objects, 9-8

product-specific, 9-9

product-specific for use with PL/SQL, 1-4

referencing, 9-4

restrictions on referencing, 9-5

scope, 9-3

serially reusable, 13-87

specification, 9-1, 13-88

specifications, 9-3

STANDARD package, 9-8

understanding, 9-1 visibility of contents, 9-1

PARALLE_ENABLE option

FUNCTION, 13-61

PARALLEL_ENABLE option

use with functions, 8-4

parameter passing

by reference, 8-24 by value, 8-24

in dynamic SQL, 7-4

parameters

actual, 6-19

actual versus formal, 8-6

in PL/SQL subprograms, 8-3

modes, 8-7

OUT mode, 8-8

summary of modes, 8-9

parentheses, 2-20

pattern matching, 2-23

performance

avoid memory overhead, 11-6

avoiding problems, 11-3

improving with PL/SQL, 1-2 performance. See also tuning

physical rowids, 3-6

pipe, 9-10

PIPE ROW statement

for returning rows incrementally, 11-34

PIPELINED

function option, 11-32, 13-61

pipelined functions

exception handling, 11-39

fetching from results of, 11-35

for querying a table, 11-32 overview, 11-32

passing data with cursor variables, 11-36

performing DML operations inside, 11-38 performing DML operations on, 11-38

returning results from, 11-34

transformation of data, 11-31

transformations, 11-33

writing, 11-32

pipelines

between table functions, 11-35

returning results from table functions, 11-34

support collection types, 11-32

using table functions, 11-33

writing table functions, 11-32

pipelining

definition, 11-32

placeholders

duplicate, 7-9

PLS_INTEGER datatype, 3-4

compared to BINARY_INTEGER, xxvii

new features, xxvi

overflow condition, 3-4

range update, xxvi

PL/SQL

advantages, 1-1

anonymous blocks, 1-4

architecture, 1-18

assigning Boolean values, 2-19 assigning query result to variable, 2-19

assigning values to variables, 2-18

best practices information on OTN, xxii

blocks, 13-8

structure, 1-4

CASE expressions, 2-26

character sets, 2-1

collection types, 5-1

collections

overview, 1-16

comments, 2-7

comparisons, 2-19

compiler limitations, C-1

compiler parameter settings, 11-2, 11-28

compiler parameters, 11-1

compile-time warnings, 10-17

compiling PL/SQL code for native execution, 11-22

conditional compilation, 1-12, 2-30

constants, 1-5

control structures, 1-9, 4-1

creating Web applications and pages, 2-38

data abstraction, 1-16

datatypes, 3-1

Index-13

debugging with JDeveloper tutorial on Oracle by

Example, xxv

declarations

constants, 2-8

demos, xxi

displaying output, 1-6, 9-9

engine, 1-18

environment, 9-8

error handling

overview, 1-18

errors, 10-1 exceptions, 10-1

expressions, 2-19

functions, 2-38, 8-1

hiding or obfuscating source code, A-1

input data, 1-15

keywords, D-1

lexical units, 2-1

limitations of programs, C-1 limits on programs, C-1

literals, 2-4

logical operators, 2-20

name resolution, B-1

naming conventions, 2-13

Oracle By Example tutorial, xxv

output data, 1-15

performance

advantage, 1-2

performance problems, 11-3

portability, 1-3

procedural aspects, 1-4

procedures, 8-1

profiling and tracing programs, 11-7

records

scope of identifiers, 2-15

Server Pages (PSPs), 2-38

syntax of language elements, 13-1

transaction processing, 6-30

tuning code, 11-2

tuning computation-intensive programs, 11-20 tuning dynamic SQL programs, 11-20

using dynamic SQL, 7-1

using NOCOPY for tuning, 11-21

using transformation pipelines, 11-31

variables, 1-5

warning messages, 10-17

Web applications, 2-38

writing reusable code, 1-13

PLSQL datatypes

numeric literals, 2-5

Index-14

PLSQL_CCFLAGS initialization parameter

conditional compilation, 2-34

native compilation, 11-28

plsql_code_type column

PLSQL_CODE_TYPE initialization parameter

setting PL/SQL native compilation, 11-26

PLSQL_DEBUG initialization parameter

PLSQL_LINE flag

for native compilation, 11-26

PLSQL_NATIVE_LIBRARY_DIR initialization parameter

Real Application Clusters with native compilation, 11-25

PLSQL_NATIVE_LIBRARY_SUBDIR_COUNT initialization parameter

for native compilation, 11-26

PLSQL_OPTIMIZE_LEVEL initialization parameter

optimizing PL/SQL programs, 11-2

use with conditional compilation, 2-33

PLSQL_UNIT flag

PLSQL_WARNINGS initialization parameter, 10-17

pointers

REF CIRSOR, 6-20

portability, 1-3

POSITIVE

POSITIVE and POSITIVEN subtypes, 3-2

POSITIVEN

compiler directive with AUTONOMOUS_

PRAGMA

TRANSACTION, 13-6, 13-61

compiler directive with AUTONOMOUS_

TRANSACTION for procedures, 13-92

compiler directive with EXCEPTION_INIT, 13-38

compiler directive with RESTRICT_

REFERENCES, 13-98

compiler directive with SERIALLY_

REUSABLE, 13-87, 13-111

pragmas

AUTONOMOUS_TRANSACTION, 6-37

compiler directives, 10-7

EXCEPTION_INIT, 10-7

RESTRICT_REFERENCES, 6-42, 7-11, 8-23

precedence, operator, 2-20

precision of digits

specifying, 3-3

predefined exceptions

raising explicitly, 10-9

redeclaring, 10-8

predicates, 6-6

PRIOR method

collections, 5-22, 13-21

PRIOR row operator, 6-5

private objects

packages, 9-8

PROCEDURE

with CREATE statement, 1-13, 1-19, 8-2

procedure declaration

syntax, 13-90

procedures

body, 8-3, 13-87

calling, 1-14, 8-4

creating, 1-13, 1-19, 8-2

declaration, 13-90

in PL/SQL, 8-1

links to examples, 13-92

parts, 8-3

recompiling with ALTER PROCEDURE, 10-19

specification, 8-3 understanding PL/SQL, 8-3

productivity, 1-3

program units, 1-13

PROGRAM_ERROR exception, 10-5

propagation

exceptions in PL/SQL, 10-9

pseudocolumns

public objects

PUT_LINE

displaying output with, 1-6

Q

qualifiers

using subprogram names as, 2-15

when needed, 2-13, 2-16

query work areas, 6-20

querying data

BULK COLLECT clause, 6-15 cursor FOR loop, 6-15

implicit cursor FOR loop, 6-16

looping through multiple rows, 6-15

maintaining, 6-19

performing complicated processing, 6-15

SELECT INTO, 6-14

using explicit cursors, 6-15

using implicit cursors, 6-16

with PL/SQL, 6-14

work areas, 6-20

quoted identifiers, 2-4

R

RAISE statement

exceptions in PL/SQL, 10-9

links to examples, 13-94 syntax, 13-94

using in exception handler, 10-11, 10-12

raise_application_error procedure

for raising PL/SQL exceptions, 10-7

raising an exception

READ ONLY parameter

setting transactions, 13-113

transactions, 6-34

READ WRITE parameter

setting transactions, 13-113

readability, 2-1

with NULL statement, 4-15

read-only transaction, 6-33

REAL

and PL/SQL native compilation, 11-25 with native compilation, 11-25

Real Application Clusters

recompiling

functions, packages, and procedures, 10-18

RECORD datatype, 5-1

record definition

syntax, 13-95

records

%ROWTYPE, 6-16

assigning values, 5-32

bulk-binding collections of, 5-36

comparing, 5-33

declaring, 5-29 defining, 5-29

definition, 1-9, 13-95

group of fields, 5-5

group of related data items, 5-1

implicit declaration, 6-16

inserting, 5-33

links to examples, 13-96

manipulating, 5-31

nesting, 5-30

overview, 1-16

passing as parameters, 5-31

restriction on assignments, 5-32

restrictions on inserts and updates of, 5-35 returning into, 5-35

ROWTYPE attribute, 5-5

updating, 5-34

using as function return values, 5-31

recursion

using with PL/SQL subprograms, 8-21

REF CURSOR datatype, 6-20 cursor variables, 6-20 defining, 6-20

using with cursor subqueries, 6-29

REF CURSOR variables

Index-15

as parameters to table functions, 11-36 predefined SYS_REFCURSOR type, 11-36

REF function

manipulating objects in PL/SQL, 12-6

reference datatypes, 3-1

references

external, 8-16

resolving external, 8-17

referencing

collections, 5-10

referencing elements

allowed subscript ranges, 5-11

regular expression functions

REGEXP_LIKE, 6-10

relational operators, 2-22

remote access indicator, 2-13

REPEAT UNTIL structure

PL/SQL equivalent, 4-9

REPLACE function

treatment of nulls, 2-30

reraising an exception, 10-11

reserved words

list of PL/SQL, D-1

PL/SQL, D-1

syntactic meaning in PL/SQL, 2-4

resolution

name, 2-14

references to names, B-1

RESTRICT_REFERENCES pragma, 8-23

links to examples, 13-99

syntax, 13-98

using with autonomous functions, 6-42

using with dynamic SQL, 7-11

restricted rowids, 3-7

restrictions

cursor expressions, 6-28

cursor variables, 6-27

overloading subprograms, 8-11

result sets, 6-9

RETURN clause

cursor, 9-11

cursor declaration, 13-31

FUNCTION, 13-62

functions, 8-4

RETURN statement

functions, 8-5

links to examples, 13-100 syntax, 13-100

return types

overloading, 8-12

REF CURSOR, 6-20

return values

functions, 8-4

RETURNING clause

links to examples, 13-102

syntax, 13-101

with a record variable, 5-35

with dynamic SQL, 7-2

returns

bulk, 11-18

Index-16

REUSE SETTINGS clause

with compiler parameters, 11-2

REVERSE

with LOOP counter, 4-10

REVERSE option

LOOP, 13-74

RNDS option

RESTRICT_REFERENCES, 13-98

RNPS option

effect on savepoints, 6-32

ROLLBACK statement, 6-31

links to examples, 13-103 syntax, 13-103

rollbacks

implicit, 6-32

of FORALL statement, 11-12

routines

external, 8-22

row locks

with FOR UPDATE, 6-34

row operators, 6-6

ROWCOUNT cursor attribute

explicit, 6-13

ROWID

ROWID datatype, 3-6 rowids, 3-6

ROWIDTOCHAR function, 6-5

ROWNUM

effect of default value, 2-11 effect of NOT NULL constraint, 2-11

ROWTYPE attribute

declaring, 1-9

inherited properties from columns, 13-104

links to examples, 13-105

ROWTYPE_MISMATCH exception, 10-5

RPC (remote procedure call)

and exceptions, 10-10

rules

purity, 8-23

run-time errors

PL/SQL, 10-1

S

samples

PL/SQL, xxi

SAVE EXCEPTIONS clause

FORALL, 13-57

SAVEPOINT statement, 6-31

links to examples, 13-106 syntax, 13-106

savepoints

reusing names, 6-32

scalar datatypes, 3-1

scale

specifying, 3-3

scientific notation, 2-5

scope, 2-15

collection, 5-6

definition, 2-15

exceptions in PL/SQL, 10-6

explicit cursor, 6-9 explicit cursor parameter, 6-9

identifier, 2-15

loop counter, 4-11

package, 9-3

searched CASE expression, 2-27

searched CASE statement, 4-5

SECOND

datatype field, 3-12

security

SQL injection, 7-7, 13-43

SELECT INTO statement

links to examples, 13-109

returning one row, 6-14

syntax, 13-107

selector, 2-26

SELF_IS_NULL exception, 10-5

semantics

assignment, 3-23

blank-padding, 3-24 non-blank-padding, 3-24 string comparison, 3-24

separators, 2-2

sequences

CURRVAL and NEXTVAL, 6-4

SERIALLY_REUSABLE pragma

examples, 13-111 syntax, 13-111

use with packages, 13-87

Server Pages (PSPs)

PL/SQL, 2-38

SERVEROUTPUT

displaying output from PL/SQL, 1-15

setting ON to display output, 9-9

SET clause

UPDATE, 13-121

set operators, 6-6

SET TRANSACTION statement, 6-33

links to examples, 13-114

syntax, 13-113

short-circuit evaluation, 2-21

side effects, 8-7

controlling, 8-23

SIGNTYPE

simple CASE expression, 2-26

SIGNTYPE subtype, 3-2

single-line comments, 2-7

size limit

varrays, 5-6

SMALLINT

nested tables versus arrays, 5-2

spaces

where allowed, 2-1

sparse collections

specification

spnc_commands

Oracle Metalink, 11-25

SQL

comparisons operators, 6-6

data manipulation operations, 6-1

define variables and data manipulation statements, 6-3

DML operations, 6-1

dynamic, 1-2, 7-1

exceptions raised by data manipulation statements, 6-3

injection, 7-7, 13-43

issuing from PL/SQL, 6-1

no rows returned with data manipulation statements, 6-3 pseudocolumns, 6-3

static, 1-2

SQL cursor

links to examples, 13-116

syntax, 13-115

SQL injection, 7-7, 13-43

Oracle Technology Network, 7-7, 13-43

SQLCODE function

links to examples, 13-117 syntax, 13-117

using with exception handlers, 10-14

SQLERRM function

links to examples, 13-118 syntax, 13-118

using with BULK_EXCEPTIONS ERROR_CODE field, 11-14

using with exception handlers, 10-14

standalone subprograms, 1-19

STANDARD package

defining PL/SQL environment, 9-8

START WITH clause, 6-5

statement terminator, 13-12

statements

assignment, 13-3

CASE, 13-14

CLOSE, 6-12, 6-26, 13-16

COMMIT, 13-24

DELETE, 13-36

EXECUTE IMMEDIATE, 7-2, 13-41

EXIT, 13-44

FETCH, 6-9, 6-25, 13-53

Index-17

OPEN-FOR, 6-22, 13-82

OPEN-FOR-USING, 13-82

SET TRANSACTION, 13-113

UPDATE, 13-121

WHILE-LOOP, 13-75

static constants

conditional compilation, 2-33

static expressions

boolean, 2-33

PLS_INTEGER, 2-33 use with conditional compilation, 2-33

VARCHAR2, 2-33

static SQL, 1-2

STEP clause

equivalent in PL/SQL, 4-10

STORAGE_ERROR exception, 10-5

raised with recursion, 8-22

store tables, 5-6

stored subprograms

in Oracle database, 1-19

string comparison semantics, 3-24

string literals, 2-6

NCHAR, 2-6

STRING subtype, 3-8

subprograms

actual versus formal parameters, 8-6

advantages in PL/SQL, 8-2

AUTHID clause, 8-15, 8-16

calling external, 8-22

calling from SQL*Plus, 1-20

calling with parameters, 8-7

controlling side effects, 8-23

current user during execution, 8-16

declaring nested, 8-5

declaring PL/SQL, 1-8

default parameter modes, 8-9

definer's rights, 8-15

EXECUTE privilege, 8-18

external references, 8-16

granting privileges on invoker's rights, 8-18

guidelines for overloading, 8-10

how calls are resolved, 8-12

IN OUT parameter mode, 8-8

IN parameter mode, 8-7

in PL/SQL, 8-1

invoker's rights, 8-15

Index-18

local, 1-19

mixed notation parameters, 8-7 named parameters, 8-7

OUT parameter mode, 8-8

overloading and inheritance, 8-14

overloading names, 8-10

overriding name resolution, 8-17

packaged, 1-19

parameter aliasing, 8-24

parameter modes, 8-7, 8-9

passing parameter by value, 8-24

passing parameters, 8-6

passing parameters by reference, 8-24

positional parameters, 8-7

procedure versus function, 8-4

recursive, 8-21

resolving external references, 8-17

restrictions on overloading, 8-11

roles with invoker’s rights, 8-19

standalone, 1-19 stored, 1-19

understanding PL/SQL, 8-1

using database links with invoker’s rights, 8-19

using recursion, 8-21

using triggers with invoker’s rights, 8-19 using views with invoker’s rights, 8-19

subqueries

correlated, 6-18

using in PL/SQL, 6-17

SUBSCRIPT_BEYOND_COUNT exception, 10-5

SUBSCRIPT_OUTSIDE_LIMIT exception, 10-5

substitutability of object types

with overloading, 8-14

SUBSTR function

using with SQLERRM, 10-14

subtypes

BINARY_INTEGER, 3-2

CHARACTER, 3-5

compatibility, 3-19

constrained versus unconstrained, 3-18 defining, 3-18

NATURAL and NATUARALN, 3-2

NUMBER, 3-4

PL/SQL, 3-17

POSITIVE and POSITIVEN, 3-2

synonyms

name resolution, 8-17

syntax

assignment statement, 13-3

AUTONOMOUS_TRANSACTION pragma, 13-6

BEGIN, 13-10

block declaration, 13-8

CASE statement, 13-14

CLOSE statement, 13-16

collection definition, 13-17

collection method, 13-20

comment, 13-23

constant, 13-25

cursor attributes, 13-28

cursor declaration, 13-33

cursor variables, 13-30

DECLARE, 13-11

DELETE statement, 13-36

diagram reading, 13-1

END, 13-11

EXCEPTION, 13-11

exception definition, 13-39

EXCEPTION_INIT pragma, 13-38

EXECUTE IMMEDIATE statement, 13-41

EXIT statement, 13-44

expression, 13-45

FETCH statement, 13-53

FORALL statement, 13-56

FOR-LOOP statement, 13-73

function declaration, 13-59

GOTO statement, 13-63

IF statement, 13-64

INSERT statement, 13-66

label, 13-12

literal declaration, 13-68

LOCK TABLE statement, 13-71

LOOP statement, 13-72

NULL statement, 13-77

object type declaration, 13-78

of PL/SQL language elements, 13-1

OPEN statement, 13-80

OPEN-FOR statement, 13-82

OPEN-FOR-USING statement, 13-82

package declaration, 13-85

procedure declaration, 13-90

RAISE statement, 13-94

record definition, 13-95

RESTRICT_REFERENCES pragma, 13-98

RETURN statement, 13-100

RETURNING clause, 13-101

ROLLBACK statement, 13-103

ROWTYPE attribute, 13-104

SAVEPOINT statement, 13-106

SELECT INTO statement, 13-107

SERIALLY_REUSABLE pragma, 13-111

SET TRANSACTION statement, 13-113

SQL cursor, 13-115

SQLCODE function, 13-117

SQLERRM function, 13-118

TYPE attribute, 13-119

UPDATE statement, 13-121

variable, 13-25

WHILE-LOOP statement, 13-75

SYS_INVALID_ROWID exception, 10-5

SYS_REFCURSOR type, 11-36

T

TABLE datatype, 5-6

table functions

examples on Oracle Technology Network, 11-32

exception handling, 11-39

fetching from results of, 11-35

for querying, 11-32 information on Oracle Technology

Network, 11-32

organizing multiple calls to, 11-35

passing data with cursor variables, 11-36

performing DML operations inside, 11-38 performing DML operations on, 11-38

pipelining data between, 11-35

returning results from, 11-34

setting up transformation pipelines, 11-31

using transformation pipelines, 11-33

writing transformation pipelines, 11-32

TABLE operator

manipulating objects in PL/SQL, 12-8

tabs, 2-2 terminator, statement, 2-2

ternary operators, 2-19

THEN clause

using, 4-2 with IF statement, 4-2

TIMEOUT_ON_RESOURCE exception, 10-5

TIMESTAMP datatype, 3-13

TIMESTAMP WITH LOCAL TIME ZONE datatype, 3-15

TIMESTAMP WITH TIME ZONE datatype, 3-14

TIMEZONE_ABBR

TIMEZONE_HOUR

TIMEZONE_MINUTES

TIMEZONE_REGION

TOO_MANY_ROWS exception, 10-5

trailing blanks, 3-25

transactions, 6-3

autonomous in PL/SQL, 6-37

committing, 6-30

context, 6-39

ending properly, 6-33

processing in PL/SQL, 6-3, 6-30

properties, 6-33 read-only, 6-33

restrictions, 6-34

rolling back, 6-31 savepoints, 6-31

visibility, 6-39

triggers

as a stored PL/SQL subprogram, 1-20

autonomous, 6-41

TRIM method

collections, 5-24, 13-21

TRUE value, 2-7

TRUST option

allocate large VARCHAR2 variables, 11-6 avoid memory overhead, 11-6

tuning

Index-19

compiling PL/SQL code for native execution, 11-22

computation-intensive programs, 11-20

do not duplicate built-in functions, 11-5

dynamic SQL programs, 11-20

guidelines for avoiding PL/SQL performance problems, 11-3

improve code to avoid compiler warnings, 11-7

information on Oracle Technology Network, 11-1

make function calls efficient, 11-3

make loops efficient, 11-4

make SQL statements efficient, 11-3

optimizing PL/SQL programs, 11-2

pin packages in the shared memory pool, 11-7

PL/SQL code, 11-2

profiling and tracing, 11-7

reducing loop overhead, 11-8

reorder conditional tests to put least expensive first, 11-5

use BINARY_FLOAT or BINARY_DOUBLE for floating-point arithmetic, 11-6 use PLS_INTEGER for integer arithmetic, 11-6

using DBMS_PROFILE and DBMS_TRACE, 11-7

using FORALL, 11-9

using NOCOPY, 11-21

using transformation pipelines, 11-31

TYPE attribute

declaring, 1-8

effect of default value, 2-10 effect of NOT NULL constraint, 2-10

inherited properties from column, 13-119

links to examples, 13-120

syntax, 13-119

using, 2-10

with SUBTYPE, 3-18

TYPE definition

associative arrays, 5-7

collection, 5-6 collection types, 5-6 nested tables, 5-6

RECORD, 5-29

REF CURSOR, 6-20

VARRAY, 5-6

U

unary operators, 2-19

underscores, 2-3

unhandled exceptions

catching, 10-15

propagating, 10-9

uninitialized object

how treated in PL/SQL, 12-3

UNION ALL set operator, 6-6

UNION set operator, 6-6

universal rowids, 3-6

UPDATE statement

links to examples, 13-123

syntax, 13-121

Index-20

with a record variable, 5-34

URL (uniform resource locator), 9-10

UROWID

setting transactions, 13-113

UROWID datatype, 3-6

USE ROLLBACK SEGMENT parameter

user-defined

exceptions in PL/SQL, 10-5

records, 5-1

subtypes, 3-17

USING clause

EXECUTE IMMEDIATE, 13-42

with dynamic SQL, 7-2

with EXECUTE IMMEDIATE, 13-42

with OPEN FOR statement, 13-83

UTF8 character encoding, 3-9

UTL_FILE package, 9-10

UTL_HTTP package, 9-10

UTL_SMTP package, 9-10

utlirp.sql script

for PL/SQL native compilation, 11-28

utlrp.sql script

for PL/SQL native compilation, 11-31

V

V$RESERVED_WORDS view

listing of reserved words and keywords, D-1

VALUE function, 12-5

VALUE_ERROR exception, 10-5

VALUES clause

INSERT, 13-67

VALUES OF clause, 11-9

FORALL, 13-56

VARCHAR subtype, 3-8

VARCHAR2 datatype, 3-8

differences with CHAR, 3-23

variables

assigning query result to, 2-19

assigning values, 1-6, 2-18

bind, 1-7, 13-82

declaring, 1-5, 2-8

declaring PL/SQL, 1-8

global, 9-8

host, 13-82

initializing, 2-18

links to examples, 13-27

passing as IN OUT parameter, 1-6

REF CURSOR datatype, 6-20

syntax, 13-25

understanding PL/SQL, 1-5

variable-size arrays (varrays)

VARRAY datatype, 5-3, 5-6

varrays

versus nested tables, 5-5

visibility

of package contents, 9-1

transaction, 6-39

versus scope, 2-15

W

warning messages

controlling PL/SQL, 10-18

Web applications

creating with PL/SQL, 2-38

Web server pages

creating with PL/SQL, 2-38

WHEN clause

exception handling, 13-39

exceptions, 10-12

using, 4-8

WHERE CURRENT OF clause

DELETE statement, 13-37

WHILE-LOOP statement

WNDS option

WNPS option

words

reserved in PL/SQL, D-1

work areas

queries, 6-20

WRAP function

obfuscation, A-4

wrap utility

obfuscating PL/SQL code, A-1

obfuscation of PL/SQL code, A-2

running, A-3

wrapped

PL/SQL source code, A-1

wrapping

DBMS_DDL package, A-4

dynamically, xxv, A-1