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
I need to write one function and one procedure to query a Oracle 10.1 DB using PL SQL. I have the schema and exact queries...along with work Ive started and a template to put the a

Using Host Arrays The Client-side programs can use anonymous PL/SQL blocks to bulk-bind input and output host arrays. However, this is the well-organized way to pass the colle

Datatypes Every constant and variable has a datatype that specifies the storage format, constraints, and the valid range of values. The PL/SQL gives a variety of predefined dat

Managing Cursors The PL/SQL uses 2 types of cursors: implicit and explicit. The PL/SQL declares a cursor implicitly for all the SQL data manipulation statements, including th

Using Subqueries A subquery is a query (typically enclosed by parentheses) that appears within another SQL data manipulation statement. If evaluated, the subquery gives a va

EXECUTE IMMEDIATE Statement   The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:

Using Savepoints The scope of the savepoint is a transaction in which it is defined. The Savepoints defined in the major transaction are not related to the savepoints defined

Using EXTEND To enlarge the size of a collection, use EXTEND. This process has 3 forms. The EXTEND appends one null element to a collection. And the EXTEND(n) appends n null e

Project Description: I want a small relational database to be built. I want the database to have the subsequent information tables: Employee Information Document storage

Controlling Cursor Variables You use 3 statements to control the cursor variable: OPEN-FOR, FETCH, & CLOSE. At First, you OPEN a cursor variable FOR a multi-row query. Then, y