Using forall statement - bulk bind performance improvement, PL-SQL Programming

Using the FORALL Statement

The keyword FORALL instruct the PL/SQL engine to bulk-bind input collections before sending them all to the SQL engine. Though the FORALL statement contain an iteration scheme, but it is not a FOR loop. The syntax for the FORALL Statement is as shown below:

FORALL index IN lower_bound..upper_bound

sql_statement;

The index can only be referenced within the FORALL statement and only as the collection subscript. The SQL statement should be an INSERT, DELETE, or UPDATE statement which references all the collection elements. And, the bounds should state the valid range of the consecutive index numbers. The SQL statement is executed by the SQL engine once for each and every index number in the range. As the example below shows, you can use the bounds to bulk-bind random slices of a collection:

DECLARE

TYPE NumList IS VARRAY(15) OF NUMBER;

depts NumList := NumList();

BEGIN

-- fill varray here

...

FORALL j IN 6..10 -- bulk-bind middle third of varray

UPDATE emp SET sal = sal * 1.10 WHERE deptno = depts(j);

END;

The SQL statement can reference more than one collection. Though, the PL/SQL engine bulk-binds only the subscripted collections. And hence, in the illustration below, it does not bulk-bind the collection sals, that are passed to the function median:

FORALL i IN 1..20

INSERT INTO emp2 VALUES (enums(i), names(i), median(sals), ...);

The next illustration shows that the collection subscript cannot be an expression:

FORALL j IN mgrs.FIRST..mgrs.LAST

DELETE FROM emp WHERE mgr = mgrs(j+1); -- illegal subscript

All the collection elements in the particular range must exist. If an element was deleted or is missing, you get an error, as the example below shows:

DECLARE

TYPE NumList IS TABLE OF NUMBER;

depts NumList := NumList(10, 20, 30, 40);

BEGIN

depts.DELETE(3); -- delete third element

FORALL i IN depts.FIRST..depts.LAST

DELETE FROM emp WHERE deptno = depts(i);

-- raises an "element does not exist" exception

END;

Posted Date: 10/4/2012 3:28:25 AM | Location : United States







Related Discussions:- Using forall statement - bulk bind performance improvement, Assignment Help, Ask Question on Using forall statement - bulk bind performance improvement, Get Answer, Expert's Help, Using forall statement - bulk bind performance improvement Discussions

Write discussion on Using forall statement - bulk bind performance improvement
Your posts are moderated
Related Questions
Use the PLS_INTEGER Datatype When you require to declare an integer variable, use the datatype PLS_INTEGER that is the most efficient numeric type. That is as the PLS_INTEGER

User-Defined Exceptions The PL/SQL defines the exceptions of your own. Dissimilar to the predefined exceptions, the user-defined exceptions should be declared and should be rai

Grouping and Ungrouping in SQL Example specifying EXAM_MARK in place of COURSE in the main FROM clause. Example: Obtaining C_ER2 from EXAM_MARK SELECT CourseId, CAST

Third Step at defining type SID in SQL CREATE DOMAIN SID AS VARCHAR(5) CHECK ( VALUE IS NOT NULL AND SUBSTRING(VALUE FROM 1 FOR 1) = 'S' AND CAST('+'||SUBSTRING(VALUE

Parameter Modes   To define the behavior of formal parameters you use the parameter modes. The 3 parameter modes, IN, OUT, & IN OUT, can be used with any subprogram. Though, a

query to Find the account numbers of all customers whose balance is more than 10,000 $

LEVEL You use the LEVEL with the SELECT CONNECT BY statement to categorize rows from a database table into a tree structure. The LEVEL returns the level number of a node in a

Dynamic SQL: The Most PL/SQL programs do a predictable, specific job. For illustration, a stored procedure may accept an employee number and salary increase, and then update t

Restriction and AND - SQL Restriction is available via the WHERE operator, and so it is in SQL. However, by Example showing how a certain simple restriction can be expressed u

Use the MASCOT tables CREDITRS, PORDS and PAYMENTS to write SQL queries to solve the following business problems. These tables / data are available to you via the USQ Oracle server