Re: Slow query
Posted by:
Rick James
Date: December 11, 2015 06:56PM
A SELECT (such as in the EXISTS) can be fast if it can use an INDEX.
"WHERE ... OR ..." cannot use any index and must scan the whole table (or at least until if finds a hit (in the case of EXISTS)).
EXISTS ( SELECT * FROM t WHERE ... )
OR
EXISTS ( SELECT * FROM t WHERE ... )
might run faster.
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