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From:Rick James Date:August 20 2012 5:57pm
Subject:RE: Hi, how did u do de-emphasis of sql statements?
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Let me change your example slightly...
select * from table where name>’A’
versus
select * from table where name>’Z’

Now, let's assume you have an INDEX starting with `name` and names are distributed in the typical way.

The will be perhaps 1% of the names satisfying >'Z', but 95% satisfying >'A'.  The index would be very useful for Z, but a waste for A.

Hence, it is a "feature" that MySQL does not cache execution plans.

You will also find that MySQL's query analyzer is very fast (compared to the competition).  Hence, there is much less need for a cache than 'they' have.

> -----Original Message-----
> From: Johan De Meersman [mailto:vegivamp@stripped]
> Sent: Monday, August 13, 2012 5:49 AM
> To: MID.night
> Cc: 673575760; mysql
> Subject: Re: Hi, how did u do de-emphasis of sql statements?
> 
> 
> 
> ----- Original Message -----
> > From: "MID.night" <693893465@qq.com>
> >
> > Like select * from table where name>’Ae name>’B’.
> 
> The execution plan for both statements is indeed likely (but not
> guaranteed!) to be the same. As far as I'm aware, though, MySQL does
> not bother about that, though, as there is no execution plan cache.
> 
> The query result cache does not equate the statements - it works based
> off the EXACT query text, INCLUDING spaces and capitalization.
> 
> When analyzing various logs, the Maatkit/Aspersa/Percona toolset does
> transform SQL statements into their canonical form, though; so if
> you're looking for ways to do that you can have a look at how it's done
> there.
> 
> 
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Thread
Hi, how did u do de-emphasis of sql statements?MID.night13 Aug
  • Re: Hi, how did u do de-emphasis of sql statements?Johan De Meersman13 Aug
    • RE: Hi, how did u do de-emphasis of sql statements?Rick James20 Aug