On 03/02/2012 08:30, Chris Travers wrote:
On Fri, Feb 3, 2012 at 12:26 AM, garry <garry@xxxxxxxxxxxxxxx>
wrote:
I have a table which holds a user name and their results in
exams. There can be multiple entries per user. I am trying to
return the last entry for each user. I can get the last entry
in the table using the order by/limit method but how would
this be applied per user. My table definition is like the
following:
gradeid serial primary key,
user text,
grade char(1),
entered timestamp,
Any help would be appreciated.
Regards
What about a combination of a common table _expression_ and a
windowing function? You ought to be able to order by your
criteria and then pull where the rowcount in the window is 1.
Best Wishes,
Chris Travers
Garry
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There is no simple solution like there is for the last row in the
table.
Window functions are one option, sub queries are another:
SELECT *
FROM results,
( SELECT student_id,
max(result_date) result_date
FROM results
GROUP BY student_id
) as latest
WHERE results.student_id = latest.student_id
AND results.result_date = latest.result_date
Note that for this to work correctly, result_date will need to be
unique.
Regards
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