Difference between revisions of "EXPLAIN"
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==See Also== | ==See Also== | ||
| − | [[CLOSE ALTERNATE]], [[CREATE INDEX]], [[INDEX]], [[PROFILE]], [[SQL SELECT|SELECT]], [[SET ALTERNATE]], [[SET CONSOLE]], [[SQLCNT]] | + | [[CLOSE ALTERNATE]], [[CREATE INDEX]], [[INDEX]], [[PROFILE]], [[SQL SELECT|SELECT]], [[SET ALTERNATE]], [[SET CONSOLE]], [[SET EXPLAIN]], [[SQLCNT]] |
==Description== | ==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 | + | 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 performance of SELECT statements. |
| + | |||
| + | Note: from Lianja v2.1, issuing [[SET EXPLAIN|SET EXPLAIN ON]] causes all executed SQL SELECT commands to output their EXPLAIN execution plan to the console. | ||
==Example== | ==Example== | ||
Revision as of 05:59, 14 June 2016
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, SET EXPLAIN, 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 performance of SELECT statements.
Note: from Lianja v2.1, issuing SET EXPLAIN ON causes all executed SQL SELECT commands to output their EXPLAIN execution plan to the console.
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
Lianja Server, Lianja
