Re: last entry per person

On 03/02/2012 08:30, Chris Travers wrote:

On Fri, Feb 3, 2012 at 12:26 AM, garry <garry@scholarpack.com> 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