Re: Index optimization ?

On Sat, Jan 15, 2005 at 01:27:49PM -0500, Tom Lane wrote:
> Bo Lorentsen <bl(at)netgroup(dot)dk> writes:
> > select * from sale where id = currval( 'sale_id_seq' );
>
> This is not legally optimizable into an indexscan, because currval() is
> a volatile function. (It's easy to construct cases where its value
> actually does change from row to row --- just use a nextval() as well.)
>
> You can fake it out in a couple of ways --- the recommended method is to
> wrap currval in a user-defined function that is misleadingly marked
> stable. I think it still works to just put the call in a sub-select:
> select * from sale where id = (select currval( 'sale_id_seq' ));
> but I take no responsibility if future improvements in the planner break
> that trick.

Would it make sense to have a version of currval that will only return
one value in a statement/transaction? So the first time it's called it
remembers what currval for that sequence is and always returns the same
value?
--
Jim C. Nasby, Database Consultant decibel(at)decibel(dot)org
Give your computer some brain candy! www.distributed.net Team #1828

Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"