Re: *very* inefficient choice made by the planner (regarding

From: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
To: Jean-Luc Lachance <jllachan(at)sympatico(dot)ca>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org, Frank van Vugt <ftm(dot)van(dot)vugt(at)foxi(dot)nl>
Subject: Re: *very* inefficient choice made by the planner (regarding
Date: 2004-06-10 17:14:36
Message-ID: 20040610101410.X21002@megazone.bigpanda.com
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On Thu, 10 Jun 2004, Stephan Szabo wrote:

>
> On Thu, 10 Jun 2004, Jean-Luc Lachance wrote:
>
> > I agree, but it should be a simple rewrite. No?
>
> It's NULLs inside the subselect that are the issue.
>
> select 1 in (select a from foo)
> select exists ( select 1 from foo where a=1)
>
> If foo.a contains a row with NULL but no rows containing a 1, the above
> give different results (unknown and exists) and IIRC, exists cannot

Erm that exists should have been false

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