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Using MySQL's Analysis Tools to Improve Query Performance

Feb 19, 2011, 15:04 (1 Talkback[s])
(Other stories by Rob Gravelle)


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"MySQL's Explain Extended Explained

"One nice feature added to the EXPLAIN statement in MySQL 4.1 is the EXTENDED keyword which provides you with some helpful additional information on query optimization. It should be used together with SHOW WARNINGS to get information about how query looks after transformation as well as what other notes the optimizer may wish to tell us. This article will demonstrate how to use Explain Extended with Show Warnings to fine tune your Select statements as well as how to rev up performance even more using optimizer hints and SHOW STATUS.

"What the Extended Keyword Adds

"While it may look like a regular Explain statement, behind the scenes, MySQL engineers the SQL statement into its optimized form. Using Show Warnings afterwards prints out the optimized Select statement. Examining it can give us a better idea of how MySQL is interpretting our SQL. Here's an example:

"The following query could be used to find how many employees show up in the bonuses table. That is to say, how many employees have received bonuses:"

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