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Re: Performance of Dependent Subquery
Posted by: KimSeong Loh
Date: October 24, 2004 08:06PM

I don't know why.

But, from the 2 EXPLAIN results, both queries choose to use different index.
Query 1 uses index (week) and expect to get 48034 rows
Query 2 uses index (ObjectID) and expect to get 2009 rows.

So, 1 possible explanation is that MySQL unables to decide properly which index is better in Query 1 due to the subquery. You can try to force MySQL to use index (ObjectID) in query 1 and becnhmark it.

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