MySQL Performance Tuning
Syntax
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Don't use DISTINCT and GROUP BY in the same SELECT.
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Don't paginate via OFFSET, "remember where you left off".
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WHERE (a,b) = (22,33) does not optimize at all.
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Explicitly say ALL or DISTINCT after UNION -- it reminds you pick between the faster ALL or the slower DISTINCT.
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Don't use SELECT *, especially if you have TEXT or BLOB columns that you don't need. There is overhead in tmp tables and transmission.
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It is faster when the GROUP BY and ORDER BY can have exactly the same list.
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Don't use FORCE INDEX; it may help today, but will probably hurt tomorrow.
Remarks
See also discussions about ORDER BY, LIKE, REGEXP, etc. Note: this needs editing with links and more Topics.
