Question

I want to select Info by timestamp and UnitID. Heres the two tables:

Table Info:

 ID | UnitID |       Time            | Info   
 -----------------------------------------------
 1  |  101   |  2011-07-20 08:22:02  |  info 101
 2  |  102   |  2011-07-21 08:22:02  |  info 102
 3  |  103   |  2011-07-22 08:22:02  |  info 103
 4  |  104   |  2011-07-23 08:22:02  |  info 104
 5  |  104   |  2011-07-25 08:22:02  |  info 104
 6  |  102   |  2011-07-26 08:22:02  |  info 102

The results I want is one for each UnitID and latest Time (timestamp) for this UnitID as:

 ID | UnitID |       Time             |  Info   
 ------------------------------------------------
 1  |  101   |   2011-07-20 08:22:02  |  info 101
 3  |  103   |   2011-07-22 08:22:02  |  info 103
 5  |  104   |   2011-07-25 08:22:02  |  info 104
 6  |  102   |   2011-07-26 08:22:02  |  info 102

How do I make this Query?

Answer 1

SELECT t1.ID, t1.UnitID, t2.MaxTime, t1.Info
FROM Info t1
INNER JOIN (SELECT UnitID, MAX(Time) As MaxTime 
            FROM Info
            GROUP BY UnitID) AS t2
ON (t1.UnitD = t2.UnitID AND t1.Time = t2.MaxTime)