Hi!
On Mon, 21 Aug 2000, Hannu Krosing wrote:
> And predictability is GOOD ;)
>
> I would even suggest that PG would warn about or even refuse to run
> queries
> that have both nextval and curval of the same sequence inside them
> (and pre-evaluate nextval) as only that case has _any_ predictability.
Isn't the problem more general than just nextval? Any user defined
function with side-effects would be a problematic one... plus a user
defined function might not be constant:
select ... from ... where x in (select side_effects(x) ...) On correlated subqueries there is no guarantee of being
constant.
In Prolog, which is a declarative language with some similarities to
relational algebra the ideia is: "if you use predicates with side effects,
then you're on your own".
Tiago
PS - Apologies for any irrelevant comment, I'm just starting to look to pg
code.