Re: bad Join Performance
Posted by:
Rick James
Date: November 02, 2011 06:23AM
FROM base
INNER JOIN base REV0 USE INDEX(tag_hash) ON REV0.`hash`=base.`hash`
INNER JOIN base REV1 USE INDEX(tag_hash) ON REV1.`hash`=base.`hash`
Why the heck do you have the same table 3 times? Is `hash` unique? If so, it makes no sense; you could simply use one copy of the table. If there are 10 rows with a given `hash`, you are asking for 1000 rows in this JOIN (10*10*10). Why?
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