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Re: Fails to use range index in outer joined table
Posted by: Øystein Grøvlen
Date: May 27, 2011 06:14AM

The MySQL's range optimizer can not handle ref access, only range access. In your second example, where adid is constant, the entire range is known at optimize time, and the range optimizer will find that the index can be used to cover the entire range. In the original example, where the range will vary for each access of table2, MySQL will not consider this kind of optimization.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway

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