MySql使用两个表和Timestamp选择Distinct

Question

我想按时间戳和UnitID选择Info。下面是两张桌子：

表格信息：

 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

我想要的结果是每个UnitID一个，以及此UnitID的最新时间（时间戳）：

 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

如何进行此查询？

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)

Answer 2

试试这个 -

SELECT t1.* FROM table1 t1
JOIN (
  SELECT UnitID, MAX(Time) maxtime FROM table1 GROUP BY UnitID
) t2
ON t1.UnitID = t2.UnitID AND t1.Time = t2.maxtime;

使用实际的表名更改'table1'。

Answer 3

也许这个？

SELECT * FROM Info GROUP BY UnitID HAVING Time = MAX(Time);