Message-ID: <3E47F056.DE8707E2@nsd.ca>
Date: Mon, 10 Feb 2003 13:32:54 -0500
From: Jean-Luc Lachance <jllachan@nsd.ca>
MIME-Version: 1.0
To: "Ross J. Reedstrom" <reedstrm@rice.edu>
Cc: "A.M." <agentm@cmu.edu>, pgsql-sql@postgresql.org
Subject: Re: order by date desc but NULLs last
References: <F427C52A-3C7D-11D7-A094-0030657192DA@cmu.edu>
	<20030209231204.GB11550@wallace.ece.rice.edu>
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Why not try the obvious first?

order by gradedtime is null, gradedtime desc;


"Ross J. Reedstrom" wrote:
> 
> On Sun, Feb 09, 2003 at 05:29:29PM -0500, A.M. wrote:
> > I have a simple query that sorts by descending date but the NULL dates
> > show up first. Is there a way I can sort so they come last without
> > sorting ascending?
> >
> > SELECT submittime,score,gradedtime FROM student_gradedmaterial WHERE
> > gradedmaterialid=3 and studentid=102 order by gradedtime desc;
> >
> >      submittime      | score |         gradedtime
> > ---------------------+-------+----------------------------
> >  2003-01-30 22:56:38 |       |
> >  2003-01-31 03:42:29 |    99 | 2003-02-06 14:21:43.043587
> >
> > but what I want is all the graded items first in gradedtime desc and
> > NULL afterwards. I do need to keep the NULL score rows. (So I get the
> > latest submitted grade for the assignment but also any ungraded
> > submission information.)
> 
> You need to ORDER BY a _function_ of the gradedtime column, substituting
> an extreme value for NULL. Try this:
> 
>  SELECT submittime,score,gradedtime FROM student_gradedmaterial
>  WHERE gradedmaterialid=3 and studentid=102 order by
>  coalesce(gradedtime,'-infinity') desc;
> 
> Ross
> 
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