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Re: Slow left outer join

  • From: Alexander Staubo <alex(at)purefiction(dot)net>
  • To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
  • Cc: PgSQL General <pgsql-general(at)postgresql(dot)org>
  • Subject: Re: Slow left outer join
  • Date: Mon, 27 Nov 2006 10:34:21 +0100
  • Message-id: <E42CBF48-B44F-48C4-8746-1BD10F359E39(at)purefiction(dot)net>
On Nov 27, 2006, at 02:45 , Tom Lane wrote:


Alexander Staubo <alex(at)purefiction(dot)net> writes:

select comments.*, users.*
from comments
left outer join users on
   users.id = comments.creator_id
inner join events_comments on
   comments.id = events_comments.comment_id
   and events_comments.event_id = 9244



The outer join seems unnecessarily slow.
Try flipping the order of the two joins. PG 8.2 will be smart enough to 
do that for itself, but no existing release understands when it's safe
to rearrange outer-join order.


That fixes it. Thanks.

Alexander.
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