On Wed, Sep 19, 2012 at 12:34 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Wed, Sep 19, 2012 at 10:30 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> To do what you want, I'd suggest wrapping the join into a sub-select >>> with an "OFFSET 0" clause, which will serve as an optimization fence >>> that prevents the random() call from being pushed down. > >> You've repeatedly objected to complaints on pgsql-performance on the >> grounds that WITH is an optimization fence. It seems awfully >> inconsistent to turn around and say, oh, sometimes it's not a fence >> after all. > > Huh? The join in question is not inside a WITH. If it were, that > would work too, as noted by Merlin.
Oh, hmm. I see now: the problem isn't that random() is being pushed into the WITH, it's that it's being pushed into the join. Sorry, I should have read that more carefully. It still seems like awfully weird behavior. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
