Re: Behavior of nextval() and currval()

Bruce Momjian wrote:
>
> So you are asking if the order of column function evaluations is
> reliable.  I tend to think so.  I think the only thing that could
> reorder it is rules.

and

Tom Lane wrote:
>
> Mike Mascari <mascarm@mascari.com> writes:
> > The following works in 7.1. Is this behavior guaranteed or is it the
> > subject of possible change in the future? Or am I just "getting
> > lucky" that nextval() is evaluated before currval():
>
> > SELECT nextval('s'), currval('s');
>
> Hmm.  SELECT target expressions are indeed evaluated left to right at
> present, and I don't see any reason to change that --- but it's not
> guaranteed by the spec AFAIK.  I think you're right to be wary of
> depending on it.  Why would you need to do this anyway?

It's an odd scenario, where I need to generate primary keys from an
INSERT..SELECT and the secondary field should match the primary key
in this instance. The secondary field represents a "parent" which
refers to itself if the record is not a child (as opposed to say,
0). I've switched to using a CREATE TEMPORARY TABLE AS SELECT..,
INSERT..SELECT to avoid the scenario.

Thanks,

Mike Mascari
mascarm@mascari.com

>
>                         regards, tom lane