From: Sergei Golubchik
Date: January 9 2011 3:41pm
Subject: Re: Optimization about count(*)
List-Archive: http://lists.mysql.com/internals/38230
Message-Id: <20110109154122.GA16230@janus.mylan>
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Hi, ??????!

On Jan 09, ?????? wrote:
> sql:
> select count(*) from t where id > 10 and id < 1000000;
> In table t, there is an B-tree index on id field, this sql will read
> hundreds of thousandes of lines from the storage engine, this is a
> time-consuming operation.
> If tell the storage engine computing the count in the range, does it
> have higher performance? (using records_in_range() api and so on)

There's no API for that in MySQL yet.
records_in_range() is approximate, it cannot be used for count(*).

Regards,
Sergei