Re: group by can use alias from select list

On Tue, Jul 11, 2023 at 7:19 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
wrote:

> On Fri, 2023-07-07 at 07:36 +0000, PG Doc comments form wrote:
> > i have a discussion in pgsql-bugs(at)lists(dot)postgresql(dot)org about this and
> it is
> > mentioned in the answers that it is documented and a "feature" of
> Postgres
> > that this can be done.
> > If this is wanted the documentation
> > (https://www.postgresql.org/docs/current/sql-select.html) that
> mentioned:
> > [execution order of SELECT that says that GROUP BY is before SELECT]
> > isn't correct because how can 4.) be done and the alias from 5.) is
> used?
> > Here is a hint important that there is an exception for alias used in
> group
> > by
>
> I think that is already documented:
>
>
I think the complaint is that someone seeing the behavior in the wild comes
to this order-of-operations and doesn't see that the observed behavior is
documented. Sure, they can go into the GROUP BY section and figure out
that there is a "oh, by the way" comment within there that output
columns/aliases are indeed allowed. But I tend to agree that a mention in
the "order of operations" section that output columns from step 5 can be
seen in step 4 seems like an improvement if we really want the order of
operations to be the main reference entry point for people trying to work
out query behavior. Something like: "(while unadvised it is possible for
the aliases defined in the next step to be used here as well)".

David J.