Re: order by date desc but NULLs last

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