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Re: Analyze question
Posted by: Rick James
Date: July 15, 2010 08:54PM

(InnoDB-specific discussion)

I have seen the optimizer "do the right thing" for a month, then suddenly decide to do a table scan for a day.

ANALYZE TABLE can fix the problem, or it can cause the problem.

select * from A where id=xx ---> Optimizer NOT consider cardinality
* If `id` is UNIQUE (PRIMARY), then it will always(?) use the index.
* If id=xx for most of the table, it will (probably) switch to a table scan.

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