Re: Index optimization ?

Bo Lorentsen <bl@netgroup.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.

            regards, tom lane