Re: bad selectivity estimates for CASE

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Robert Haas" <robertmhaas(at)gmail(dot)com>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: bad selectivity estimates for CASE
Date: 2009-01-06 04:40:43
Message-ID: 3032.1231216843@sss.pgh.pa.us
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"Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
> While looking at a complex query that is being poorly planned by
> PostgreSQL 8.2.9, I discovered that any non-trivial CASE...WHEN
> expression seems to produce a selectivity estimate of 0.005.

If you have an idea for a non-silly estimate, feel free to enlighten
us...

regards, tom lane

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