Re: Common Table Expressions applied; some issues remain

On Sat, Oct 4, 2008 at 5:22 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> that Oracle chooses to treat WITH-queries as if they were plain
> sub-selects if they're non-recursive and only referenced once.
> That is, Oracle would rewrite the above into
>
>        SELECT * FROM ( SELECT * FROM foo ) AS q WHERE key = 42;
>
> and then flatten the sub-select and optimize normally.  It would
> not be hard to make Postgres do the same, but then we would lose
> some guarantees about predictable execution of volatile functions.
>
[...]
>
> Any thoughts on what to do?  One possibility is to flatten only
> if the subquery doesn't contain any volatile functions.
>

maybe i'm missing something but AFAIR postgres will not try to
optimize (push down/pull up) if it see any volatile function.

--
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
Asesoría y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157