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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Josh Berkus <josh@agliodbs.com>
cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: Weird, bad 0.5% selectivity estimate for a column equal to itself
In-reply-to: <51C4AEE5.8040704@agliodbs.com>
References: <51C4AEE5.8040704@agliodbs.com>
Comments: In-reply-to Josh Berkus <josh@agliodbs.com>
 message dated "Fri, 21 Jun 2013 12:52:05 -0700"
Date: Fri, 21 Jun 2013 17:32:58 -0400
Message-ID: <25930.1371850378@sss.pgh.pa.us>
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Josh Berkus <josh@agliodbs.com> writes:
> I'm getting something really odd in 9.2.4, where the planner estimates
> that the selectivity of a column equal to itself is always exactly 0.5%
> (i.e. 0.005X).  I can't figure out where this constant is coming from,
> or why it's being applied.

See DEFAULT_EQ_SEL.  But why exactly do you care?  Surely it's a stupid
query and you should fix it.

			regards, tom lane


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