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Re: Automatic optimization of IN clauses via INNER JOIN

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>
Cc: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Hamilton <thomashamilton76(at)yahoo(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Automatic optimization of IN clauses via INNER JOIN
Date: 2009-12-19 00:22:29
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Lists: pgsql-performance
2009/12/18 Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>:
> 2009/12/18 Robert Haas <robertmhaas(at)gmail(dot)com>:
>> 2009/12/18 Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>:
>>> On Fri, Dec 18, 2009 at 2:18 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>>> NOT IN is the only that really kills you as far as optimization is
>>>> concerned.  IN can be transformed to a join.  NOT IN forces a NOT
>>>> (subplan)-type plan, which bites - hard.
>>> in a well designed database (read: not abusing NULLs) - it can be done
>>> with joins too.
>> But not by PostgreSQL, or so I believe.
> using left join ?

If at least one column in the subselect is strict, you can rewrite it
that way yourself, but the optimizer won't do it. I wish it did, but I
don't wish it badly enough to have written the code myself, and
apparently neither does anyone else.


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