From: Manfred Koizar <mkoi-pg@aon.at>
To: Dmitry Tkach <dmitry@openratings.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Debugging postmaster to fix possible bug in Postgres? Followup
Date: Fri, 14 Feb 2003 00:01:54 +0100
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References: <44sn4vgisulljq45qo35bug12sed1ll3ce@4ax.com>
	<3E4C212E.2080805@openratings.com>
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On Thu, 13 Feb 2003 17:50:22 -0500, Dmitry Tkach
<dmitry@openratings.com> wrote:
>Then it looks like postgres behaviour is still not compliant, if I read it correctly, because
>
>select x from mytable order by y;
>
>should be invalid according to this, but works just fine in postres.

Yes, this is a Postgres extension to the standard.  Your query is
handled like

	SELECT x, y FROM mytable ORDER BY y

with y being eliminated after the sort step.  This also explains why
the OP got the error message

ERROR:  Attribute t.y must be GROUPed or used in an aggregate function

because the implicitely rewritten form would look like

	SELECT COUNT(*), y FROM t WHERE ... ORDER BY y

>P.S. I think, this is a great feature actually (missed it a lot in informix),
> so, I hope, you guys won't start discussing how to fix it :-)

AFAICT there's no need to worry.  Everyone agrees that this is a good
feature and it does not break standard SQL queries.

Servus
 Manfred