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Re: Optimize sub query with large group by
Posted by: Rick James
Date: March 14, 2011 06:31PM

GROUP BY object_id -- yet you nowhere else do you mention object_id.

The group-by-trick depends on the inner query having an order by -- that way the GROUP BY at the next level can pick the right row, namely the 'first' row in each grouping.

Another topic to study is "compound indexes".

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