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Re: MySQL 5.1.31 -- Same query scans widely different # of rows
Posted by: Rick James
Date: April 09, 2011 01:13PM

Oops. No.

Filtering on both tables in a JOIN is usually poorly optimizable. The optimizer might be able to filter in one table, but lug around the potential rows while reaching into the other table to see if they are needed. This is especially problematical if you have ORDER BY and LIMIT (which is not your case). Jørgen, can you explain it better?

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