Re: group by can use alias from select list

On Tue, Jul 11, 2023 at 07:31:26AM -0700, David G. Johnston wrote:
> On Tue, Jul 11, 2023 at 7:19 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
> 
>     On Fri, 2023-07-07 at 07:36 +0000, PG Doc comments form wrote:
>     > i have a discussion in pgsql-bugs@lists.postgresql.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)".

How is the attached patch?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Only you can decide what is important to you.