SQL语句

fworkdate      fempid     fdepartment    fdaysal
2008-06-16    宋铁军    电焊组    57.6
2008-06-15    王俊虎    电焊组  50.05
2008-06-18    王俊虎    电焊组    120
2008-06-16    王晴    电焊组   102.
2008-06-16    杨明新    电焊组 190
2008-06-16    张春兵    电焊组    66.6
2008-06-16    张高峰    电焊组 188.82
2008-06-17    张高峰    电焊组 80.64
2008-06-16    张玉宝    电焊组 61.68
2008-06-16    赵德红    电焊组 79.2
2008-06-16    赵翼    电焊组 188.82
2008-06-16    朱宝科    电焊组    57.6
要求fempid这一字段中有重复的只出现时间最早的那一个,其它为空如上面的我要它成为如下
fworkdate     fempid    fdepartment fdaysal
2008-06-16    宋铁军    电焊组    57.6
2008-06-15    王俊虎    电焊组 50.05
2008-06-18        电焊组    120
2008-06-16    王晴    电焊组  102.
2008-06-16    杨明新    电焊组  109.
2008-06-16    张春兵    电焊组    66.6
2008-06-16    张高峰    电焊组 188.82
2008-06-17        电焊组 80.64
2008-06-16    张玉宝    电焊组 61.68
2008-06-16    赵德红    电焊组    79.2
2008-06-16    赵翼    电焊组 188.82
2008-06-16    朱宝科    电焊组    57.6