Обсуждение: group by

I have a problem whith group by and aliases

select s1.channelname as channelname, s1.id as channelid,
count(*) as anz from mgw_news n left join mgw_news_channels s1 on
n.channelid = s1.id group by channelid, channelname order by channelid,
channelname


this runs under mysql and postgresql seems not to accept aliases in
group by

cause when i'm changing channelid to s1.id it works perfectly

is anyone working on that?
I didn't see this in the TODO list

With whom can I talk about this problem?

regards Ewald Geschwinde

Ewald,

> select s1.channelname as channelname, s1.id as channelid,
> count(*) as anz from mgw_news n left join mgw_news_channels s1 on
> n.channelid = s1.id group by channelid, channelname order by channelid,
> channelname
>
> this runs under mysql and postgresql seems not to accept aliases in group by
>
> cause when i'm changing channelid to s1.id it works perfectly

I believe that the PostgreSQL behavior, i.e. not accepting the real names of
 columns that have been aliased, is the SQL92 standard behavior.  Certainly it
 prevents a certain confusion in the query parser in the case of multiple
 references to an aliased column.

In other words, I believe that the behavior you are observing is by design and
 is not a bug.  Please keep in mind that MySQL does *not* uphold the SQL92
 standard, so it cannot be used as an index of proper behavior.  So, change
 your GROUP BY reference.

However, the behavior you mention should certainly be mentioned in one or more
 of the porting articles at TechDocs ( http://techdocs.postgresql.org/ ).
  E-mail one of the authors if it's not.

-Josh Berkus

______AGLIO DATABASE SOLUTIONS___________________________
                                       Josh Berkus
  Complete information technology      josh@agliodbs.com
   and data management solutions       (415) 565-7293
  for law firms, small businesses        fax 621-2533
    and non-profit organizations.      San Francisco

Ewald Geschwinde <webmaster@geschwinde.net> writes:
> I have a problem whith group by and aliases

> select s1.channelname as channelname, s1.id as channelid,
> count(*) as anz from mgw_news n left join mgw_news_channels s1 on
> n.channelid = s1.id group by channelid, channelname order by channelid,
> channelname

I would expect "group by channelid" to refer to n.channelid, which is
the SQL-mandated interpretation.  Using aliases in GROUP BY is a flat
violation of the SQL92 standard, but a lot of implementations accept it
anyway.  However, when there is an ambiguous situation, as here, we must
treat GROUP BY as referring to the underlying column name not the alias,
else we do not conform to the standard.

> this runs under mysql and postgresql seems not to accept aliases in
> group by

> cause when i'm changing channelid to s1.id it works perfectly

> is anyone working on that?

No, because it's not a bug.  MySQL's behavior is not SQL92 compliant,
if you've described it accurately.

            regards, tom lane