Re: multi-part index and when it is used?
MySQL will only use 1 index per instance of a table per query.
So in your above example it would be better to use the multi-part index (a,b), because if you created two single column indices, MySQL would only use which ever one it thinks is more selective. I believe some of this may be changing in MySQL 5.0
Harrison, can correct any mistakes that I have made... =P
Jonathan Cochran
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Re: multi-part index and when it is used?
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