From: Tom Lane <tgl@sss.pgh.pa.us>
To: Martijn van Oosterhout <kleptog@svana.org>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>
Cc: pgsql-hackers@postgresql.org
Subject: Re: WITH RECUSIVE patches 0723
Date: Mon, 28 Jul 2008 19:04:14 -0400
Message-ID: <203.1217286254@sss.pgh.pa.us> (raw)
In-Reply-To: <20080728222446.GC24856@svana.org>
References: <20080725001513.GF16438@fetter.org>
<20080725.092652.105178884.t-ishii@sraoss.co.jp>
<87r69gs967.fsf@news-spur.riddles.org.uk>
<20080728.162925.23020498.t-ishii@sraoss.co.jp>
<19882.1217256991@sss.pgh.pa.us>
<87myk1rg4z.fsf@news-spur.riddles.org.uk>
<20080728222446.GC24856@svana.org>
Martijn van Oosterhout <kleptog@svana.org> writes:
> Since the problem is using the result of a WITH clause more than once,
> would it be sufficient to simply detect that case and bail? You don't
> want materialisation is most cases, there's just a few where it is
> needed.
Really? I tried googling to see what other people thought that the
WITH clause was for, and the first relevant hit I got was this one:
http://www.oracle-developer.net/display.php?id=212
which certainly treats it as a key part of the feature.
My thought is that we could optimize away materialization in cases where
we can tell it's not needed (no volatile functions and/or no multiple
scans of the subquery). But not being able to do it means we've
implemented the feature incorrectly.
regards, tom lane
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To: pgsql-patches@postgresql.org
Cc: tgl@sss.pgh.pa.us, kleptog@svana.org, andrew@tao11.riddles.org.uk, pgsql-hackers@postgresql.org
Subject: Re: WITH RECUSIVE patches 0723
In-Reply-To: <203.1217286254@sss.pgh.pa.us>
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