Difference between revisions of "EXPLAIN"

Revision as of 11:46, 26 October 2009

Purpose

Display information about the optimization and result count of an SQL SELECT statement

Syntax

EXPLAIN <SELECT statement>

See Also

CLOSE ALTERNATE, CREATE INDEX, INDEX, PROFILE, SELECT, SET ALTERNATE, SET CONSOLE, SQLCNT

Description

When an SQL SELECT statement is preceded by the EXPLAIN command, information is displayed about the optimization that would be carried out on that SELECT statement and the number of results that it would return. Analysis of the EXPLAIN output can be used by the Developer to target index creation for the maximum perfomance of SELECT statements.

Example

> EXPLAIN SELECT * FROM example
sqlcnt=100
> EXPLAIN SELECT * FROM example WHERE start_date < date()
Could not optimize WHERE condition
sqlcnt=100
> EXPLAIN SELECT * FROM example WHERE account_no = '000'
Optimized using index tag 'ACCOUNT_NO'
sqlcnt=99
 
// Send EXPLAIN output to a text file
set alternate to explain
set console off
set alternate on
EXPLAIN SELECT * FROM example
close alternate

Products

Recital Database Server, Recital Mirage Server, Recital Terminal Developer