我有一个这样的表：
CREATE TABLE Table1
(ID int, empid int, time datetime, state int);
+--------------+---------------------+-----------------+
| empid | time | state |
+--------------+---------------------+-----------------+
( 4 | 2014-03-01 11:12:00 | 0 )
( 5 | 2014-03-01 12:28:06 | 0 )
( 4 | 2014-03-01 12:50:07 | 1 )
( 4 | 2014-03-01 13:38:00 | 0 )
( 5 | 2014-03-01 13:28:06 | 1 )
( 4 | 2014-03-01 18:42:15 | 1 )
( 4 | 2014-03-02 08:11:08 | 0 )
( 4 | …