Re: functions with side effect

On Thu, Jul 19, 2018 at 6:35 PM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 07/19/2018 07:15 AM, Torsten Förtsch wrote:
> > Hi,
> >
> > assuming
> >
> > SELECT nextval('s'), currval('s');
> >
> > or
> >
> > SELECT * FROM (VALUES (nextval('s'), currval('s'))) t;
> >
> > is there any guarantee that the 2 output values are the same?
>
> Assuming you are only working in single session:
>
> https://www.postgresql.org/docs/10/static/functions-sequence.html
>
> "currval
>
> Return the value most recently obtained by nextval for this
> sequence in the current session. (An error is reported if nextval has
> never been called for this sequence in this session.) Because this is
> returning a session-local value, it gives a predictable answer whether
> or not other sessions have executed nextval since the current session did."

I know that. My question was about the execution order of f1 and f2 in
"SELECT f1(), f2()". In theory they can be executed in any order. But since
the side effect in nextval determines the result of currval, I am asking if
that order is well-defined or considered an implementation detail like in C.