根据字段组合选择最新结果

SELECt m.id, m.date_time, m.foreign_key, m.key, m.value
FROM MyTable m
LEFT OUTER JOIN MyTable mm
ON (m.foreign_key = mm.foreign_key
AND m.key = mm.key
AND m.date_time < mm.date_time)
WHERe mm.key IS NULL
AND m.foreign_key=4;

给了我我所需要的。即：

+----+---------------------+-------------+-------------+-------+| id | date_time| foreign_key | key         | value |+----+---------------------+-------------+-------------+-------+|  9 | 2010-01-01 00:00:08 |4 | humidity    |    35 || 17 | 2010-01-01 00:00:16 |4 | temperature |    19 || 18 | 2010-01-01 00:00:17 |4 | dew_point   |    24 |+----+---------------------+-------------+-------------+-------+

谢谢您的回应！