Received: from localhost (postgresql.org [64.49.215.8])
	by postgresql.org (Postfix) with ESMTP id 9A8D5475DC0
	for <pgsql-sql@postgresql.org>; Thu, 12 Dec 2002 03:32:31 -0500 (EST)
Received: from serwer.skawsoft.com.pl (serwer.skawsoft.com.pl [213.25.37.66])
	by postgresql.org (Postfix) with ESMTP id E8752475DD7
	for <pgsql-sql@postgresql.org>; Thu, 12 Dec 2002 03:32:30 -0500 (EST)
Received: from klaster.net (pr192.krakow.cvx.ppp.tpnet.pl [213.76.42.192])
	by serwer.skawsoft.com.pl (Postfix) with ESMTP
	id 82D542B266; Thu, 12 Dec 2002 09:17:16 +0100 (CET)
Message-ID: <3DF84A2D.80004@klaster.net>
Date: Thu, 12 Dec 2002 09:34:53 +0100
From: Tomasz Myrta <jasiek@klaster.net>
User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US;
	rv:1.2b) Gecko/20021016
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: "A.M." <agentm@cmu.edu>
Cc: pgsql-sql@postgresql.org
Subject: Re: Getting the latest unique items
References: <9352B184-0D90-11D7-BA9C-0030657192DA@cmu.edu>
In-Reply-To: <9352B184-0D90-11D7-BA9C-0030657192DA@cmu.edu>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-Virus-Scanned: by AMaViS new-20020517
X-Archive-Number: 200212/147
X-Sequence-Number: 10735

A.M. wrote:

> When I try to run the following query:
>
> select distinct on(student_gradedmaterial.id) student_gradedmaterial.id
> from coursesection_student,student_gradedmaterial WHERE
> gradedmaterialid=1 AND
> coursesection_student.studentid=student_gradedmaterial.studentid AND
> coursesectionid=1 and score is not null order by submittime desc;
>
> I get the following error:
>
> ERROR:  SELECT DISTINCT ON expressions must match initial ORDER BY
> expressions

No
You have to change your sort order (as in error above). It should be:
order by student_gradematerial.id asc, submittime desc;
Tomasz Myrta