From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tambet Matiisen <t.matiisen@aprote.ee>
Cc: ch@rodos.fzk.de
Cc: pgsql-sql@postgresql.org
Subject: Re: How to force subquery scan?
Date: Wed, 16 Mar 2005 10:41:52 -0500
Message-ID: <6303.1110987712@sss.pgh.pa.us> (raw)
In-Reply-To: <A66A11DBF5525341AEF6B8DE39CDE770088058@black.aprote.com>
References: <A66A11DBF5525341AEF6B8DE39CDE770088058@black.aprote.com>
"Tambet Matiisen" <t.matiisen@aprote.ee> writes:
> It seems that subquery scan is only used, when the query can not be
> translated into single flat query. Which is mostly good, I assume.
The planner thinks so anyway ;-)
If you're desperate you can put in an optimization fence, for instance
LIMIT or OFFSET.
SELECT * FROM (SELECT ... OFFSET 0) ss;
In principle the planner could figure out that this offset is a no-op,
throw it away, and then flatten the query. But it doesn't at the
moment, and I doubt we'll teach it to do so in the future.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, t.matiisen@aprote.ee, ch@rodos.fzk.de
Subject: Re: How to force subquery scan?
In-Reply-To: <6303.1110987712@sss.pgh.pa.us>
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