From: Tom Lane <tgl@sss.pgh.pa.us>
To: salah jubeh <s_jubeh@yahoo.com>
Cc: Volodymyr Kostyrko <c.kworr@gmail.com>; pgsql <pgsql-general@postgresql.org>
Sent: Thursday, January 26, 2012 5:47 PM
Subject: Re: [GENERAL] How to push predicate down
salah jubeh <
s_jubeh@yahoo.com> writes:
> Sorry, The scenario, that I posted was not correct. I have traced it and the union was not the problem, As I said the query excusion plan is over 5000 line. I have created a scenario which similar to the scenario causes the problem I have.
> [ query uses EXCEPT not UNION ]
Hmm. The code explicitly won't push conditions down through an EXCEPT:
* 3. If the subquery contains EXCEPT or EXCEPT ALL set ops we cannot push
* quals into it, because that could change the results.
I remember coming to the conclusion that this is safe for
UNION/INTERSECT but not EXCEPT, but right at the moment I'm not sure why
I thought that --- it seems like a qual that suppresses specific rows
should suppress all matching copies.
regards, tom lane
--
Sent via pgsql-general mailing list (
pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general