SQL: Select a row only if that cell has the max value given the ID

Question

I realize the title of the question is much more difficult than the question itself.

Basically I have a dataset like this one:

ID  Hour
01  1
01  2
01  3
02  1
02  2
03  1
03  2
03  3
03  4

The dataset refers to people that are playing a game. ID is, of course, the ID of the subject whilst 'Hour' refers to what happened in that hour of game. Now, I would like to select only the rows that refer to the last hour played by that player .

So that:

ID  Hour
01  3
02  2
03  4

Any ideas?

Answer 1

simply use MAX()

SELECT ID, MAX(HOUR) Max_hour
FROM   TableName
GROUP  BY ID

Answer 2

here is the solution

SELECT ID, MAX(HOUR) as Maxhour FROM Table1 GROUP BY ID

Answer 3

In the event that you actually want to select other columns on the same row, then the simple group by / max solution doesn't quite work.

One solution that works in any database that supports window functions is:

select t.*
from (select t.*,
             row_number() over (partition by id order by hour desc) as seqnum
      from TableName t
     ) t
where seqnum = 1

Answer 4

OR, if you want to make it more complicated as it is^^ this is the way to go:

select * from tablename t1 where t.hour = (select max(hour) from tablename t2 where t2.id = t1.id)