Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Sep 19, 2012 at 10:30 AM, Tom Lane <tgl@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.
regards, tom lane