Grouping - beginner's question

Question

I'm a complete beginner at SQL, and generally use it in the Discoverer admin application (so some functions aren't available)
What I need to do is return 4 values from a table. The first value is the case number. The second is (a varchar field) is the description of a particular task carried out and the third is the date it was carried out. The fourth is a task id that uniquely identifies that task in the database.
Each case has multiple tasks associated with it, and I only want to return the last one (the one with the latest date). I can find the date and case number by:
select case_id, max(actioned_date)
from tablename
group by case_id
This gives me the case number, and the date on which the final task was actioned.
however, I want to include the description and the task id, but still only group it by the case id, which I can't do in the above example, but if I include the other fields then the one result per case falls apart.
Any advice appreciated.
Thanks

Answer 1

You can do it either with subquery:
select *
from tablename
where (case_id,action_date) in (
select case_id, max(actioned_date)
from tablename
group by case_id)or eliminate subquery using first/last aggregate functions
select
min(task_id) keep (dense_rank first order by actioned_date desc),
min(description) keep (dense_rank first order by actioned_date desc),
case_id, max(actioned_date)
from tablename
group by case_idSurely, there are some other ways, but i would say, these two are more common.
Best regards
Maxim