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Re: Group by Optimization
Posted by: Björn Steinbrink
Date: December 03, 2005 06:07AM

Looks like your IDX3_PROPSTATE index does not cover PROP_STATE and PROP_CITY.
AFAIK MySQL does not use multiple keys when searching a single table, so you'd need an index that covers both, PROP_STATE and PROP_CITY, otherwise MySQL creates a temporary table with all rows that it can find using an index and does a table scan on the resulting table which holds about 3.7 million rows according to your EXPLAIN output, which creates some io action. ;)
I assume that DB2 does use more than one key at a time and thus is faster.

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