Thread: order by date desc but NULLs last

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 |
2003-02-0614:21:43.043587
 

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.)

Thanks for any advice.><><><><><><><><><
AgentM
agentm@cmu.edu

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_gradedmaterialWHERE gradedmaterialid=3 and studentid=102 order
bycoalesce(gradedtime,'-infinity')desc;
 

Ross

> 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.)
> 
> Thanks for any advice.
>  ><><><><><><><><><
> AgentM
> agentm@cmu.edu

order by gradetime is null asc, gradetime desc;

Regards,
Tomasz Myrta

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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On Mon, Feb 10, 2003 at 01:32:54PM -0500, Jean-Luc Lachance wrote:
> Why not try the obvious first?

Because it's not always obvious ;-) Yup, if you want two kinds of order
(NULLs last, descending dates), use two order by clauses. 
> order by gradedtime is null, gradedtime desc;
> 
> "Ross J. Reedstrom" wrote:

<a different, less elegant way to get the NULLs last>

Ross