Delete rows older than Max date by given ID

Question

I've a simple temp table created in a stored proc, consisting of an ID field (not primary key) and a date associated to each. What I want to do is keep only the ID/Date record which has the most recent Date, for each ID

I'd written the following, but it does not seem to be doing quite what I want

DELETE #summary
FROM #summary s1, #summary s2
WHERE s1.evt_dte != (
SELECT MAX(s1.evt_dte)
    FROM #summary s1, #summary s2
    WHERE s1.evt_or_cat_num = s2.evt_or_cat_num)
AND s1.evt_or_cat_num = s2.evt_or_cat_num

What I've tried to do is compare the table with itself and delete any records with the evt_dte less than the MAX for each evt_or_cat_num stored.

Any ideas how this can be tweaked to work correctly?

Answer 1

You could join on the data you want to keep and delete all where that link could not be made

DELETE s1
FROM #summary s1
left JOIN 
(
   select evt_or_cat_num, MAX(evt_dte) maxdt
   from #summary
   group evt_or_cat_num
) s2 on s1.evt_or_cat_num = s2.evt_or_cat_num 
    and s1.evt_dte = s2.maxdt
where s2.evt_or_cat_num is null