How to select only the latest rows for each user?

Question

My table looks like this:

id  | user_id | period_id | completed_on
----------------------------------------
1   | 1       | 1         | 2010-01-01
2   | 2                


        

Answer 1

Seems like this should work using MAX and a subquery:

SELECT t.Id, t.User_Id, t.Period_Id, t.Completed_On
FROM my_table t
   JOIN (SELECT Max(completed_on) Max_Completed_On, t.User_Id
         FROM my_table
         GROUP BY t.User_ID
         ) t2 ON
      t.User_Id = t2.User_Id AND t.Completed_On = t2.Max_Completed_On

However, if you potentially have multiple records where the completed_on date is the same per user, then this could return multiple records. Depending on your needs, potentially adding a MAX(Id) in your subquery and joining on that would work.