Get the last record of each user by eventid

Question

From the following db,

   id      userid        eventid      created_at
    1         1            100      2010-01-01
    2         1            101      2010-02-01
    3         1            100      2010-03-01
    4         1            101      2010-04-01
    5         2            100      2010-05-01
    6         2            100      2010-06-01

I'm trying to get the latest activity of of each user based on eventid, with an output like this:

6         2            100      2010-06-01
4         1            101      2010-04-01
3         1            100      2010-03-01

Answer 1

Use group by and aggregation

select userid,envid,max(id) as id, max(created_at) as created_at
from tablename a
group by userid,envid

Answer 2

Use Rownumber

SELECT *
FROM (SELECT ROW_NUMBER() OVER (PARTITION BY userid, eventid ORDER BY id DESC) as RId,
             t.*
      FROM Tablename t
     ) T
WHERE RId = 1 ;