From: | "Mattias Kregert" <mattias(at)kregert(dot)se> |
---|---|
To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Strange plan in pg 8.1.0 |
Date: | 2006-10-30 15:38:13 |
Message-ID: | 003e01c6fc39$6970bf90$09000a0a@kregert.se |
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Lists: | pgsql-performance |
From: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> Mattias Kregert <mattias(at)kregert(dot)se> writes:
>> Why does it come up with this strange plan?
>
> Because 8.1 can't reorder outer joins. To devise the plan you want,
> the planner has to be able to prove that it's OK to perform the IN join
> before the LEFT join, something that isn't always the case. 8.2 can
> prove this, but no existing release can.
>
> The only workaround I can think of is to do the IN in a sub-select.
>
> regards, tom lane
>
Thanks!
I'll try some subselect solution for now, and make a note to change it when
8.2 is out.
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