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Re: Slow views

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: David Newall <davidn-postgres(at)rebel(dot)net(dot)au>
Cc: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>,PostgreSQL bugs <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: Slow views
Date: 2004-07-17 05:00:55
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
David Newall <davidn-postgres(at)rebel(dot)net(dot)au> writes:
> It's clearly an optimisation issue:

No, it's an outer-join-semantics issue.

> select * from a join b optimises differently to select * from a join
> (select * from b) as b

The above claim is provably false.  Now, if you throw in some more
tables and sprinkle in a LEFT JOIN instead of just JOIN here and there,
you can get different plans --- but the semantics are not necessarily
the same, either.

			regards, tom lane

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