Question

Given a very simplified table with the columns

  Name, Action, Status,   Timepoint
1 "A"   "Open"  "OK"      "2012-09-04 10:10:00"
2 "A"   "Close" "OK"      "2012-09-04 10:05:00"
3 "A"   "Close" "ERROR"   "2012-09-04 10:02:00"
4 "B"   "Look"  "NICE"    "2012-09-04 10:05:00"
5 "B"   "Blow"  "COLD"    "2012-09-04 10:00:00"
6 "C"   "Laugh" "OK"      "2012-09-04 10:02:00"
7 "C"   "Laugh" "MUTE"    "2012-09-04 10:00:00"

How do I most efficiently select each row for a combination of Name and Action but only of the Action of the newest Timepoint?
In the above example it would return rows

1, 2, 4, 5, 6

The working implementation fetches the rows and uses a sub query to only return if there are 0 rows with the same Name, Action combination of a newer Timepoint. But that seems very inefficient when the data set becomes large. It’s something like this

SELECT Name, Action, Status, Timepoint
FROM foobar
WHERE Name IN (... Names of interest ...) AND 
Status IN (... statuses of interest ...) AND
(SELECT COUNT(*) FROM foobar AS t2 WHERE t2.Name = Name AND t2.Status = Status AND t2.Timepoint > Timepoint) = 0
order by Name, Timepoint

Answer 1

Select *
from 
(
      select *,
             row_number() over (partition by Name, Action order by timepoint desc) RN
      from yourtable
) v
where RN = 1