Re: problem with volatile functions in subselects ?

On 7/30/06, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Sergey E. Koposov" <math@sai.msu.ru> writes:
> > I see the very strange behaviour with the following set of queries:
>
> > wsdb=# select na,nb, na::double precision as da, nb::double precision  as db from ( select random()::numeric as
na,random()::numericas nb from generate_series(1,2)) as xx;
 
>
> The planner "flattens" this query to a single level of SELECT, so what
> you effectively have is
>
> select random()::numeric as na,
>        random()::numeric as nb,
>        random()::numeric::double precision as da,
>        random()::numeric::double precision as db
> from generate_series(1,2) as xx;
>
> There's been some talk about prohibiting flattening if there are any
> volatile functions in the subselect's targetlist, but nothing's been
> done about that.  Disabling flattening is a sufficiently big hit to
> the planner's optimization ability that it shouldn't be done lightly.
>
>                         regards, tom lane
>

http://archives.postgresql.org/pgsql-hackers/2005-10/msg00396.php

maybe a guc?

-- 
regards,
Jaime Casanova

"Programming today is a race between software engineers striving to
build bigger and better idiot-proof programs and the universe trying
to produce bigger and better idiots.
So far, the universe is winning."                                      Richard Cook