Re: Common Table Expressions applied; some issues remain

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <stark(at)enterprisedb(dot)com>
Cc: Yoshiyuki Asaba <y-asaba(at)sraoss(dot)co(dot)jp>, Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Common Table Expressions applied; some issues remain
Date: 2009-05-27 13:44:33
Message-ID: 7826.1243431873@sss.pgh.pa.us
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Greg Stark <stark(at)enterprisedb(dot)com> writes:
> On Wed, May 27, 2009 at 12:47 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I'm not too thrilled about that solution because it still eliminates
>> predictability of execution of volatile functions.

> How so? It means the volatile function might only be executed for the
> matching rows

Exactly. If the point of the CTE is to ensure that nextval() is
executed N times, and it actually gets executed less than that,
then we've broken the semantics in a visible way.

regards, tom lane

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