Difference between revisions of "EXPLAIN"
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==Class== | ==Class== | ||
Performance and Optimization | Performance and Optimization | ||
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==Purpose== | ==Purpose== | ||
| − | + | Display information about the optimization and result count of an SQL SELECT statement | |
==Syntax== | ==Syntax== | ||
| − | + | EXPLAIN <SELECT statement> | |
==See Also== | ==See Also== | ||
| − | [[SQL SELECT|SELECT]], [[SQLCNT]] | + | [[CLOSE ALTERNATE]], [[CREATE INDEX]], [[INDEX]], [[PROFILE]], [[SQL SELECT|SELECT]], [[SET ALTERNATE]], [[SET CONSOLE]], [[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 perfomance of SELECT statements. | |
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Optimized using index tag 'ACCOUNT_NO' | Optimized using index tag 'ACCOUNT_NO' | ||
sqlcnt=99 | sqlcnt=99 | ||
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| + | // Send EXPLAIN output to a text file | ||
| + | set alternate to explain | ||
| + | set console off | ||
| + | set alternate on | ||
| + | EXPLAIN SELECT * FROM example | ||
| + | close alternate | ||
</code> | </code> | ||
Revision as of 15:40, 12 October 2009
Class
Performance and Optimization
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
