查询：
SQLFIDDLE示例
SELECt t1.*FROM lms_attendance t1WHERe t1.time = (SELECt MAX(t2.time) FROM lms_attendance t2 WHERe t2.user = t1.user)
结果：
| ID | USER | TIME | IO |--------------------------------| 2 | 9 | 1370931664 | out || 3 | 6 | 1370932128 | out || 5 | 12 | 1370933037 | in |
每次都会起作用的解决方案：
SQLFIDDLE示例
SELECt t1.*FROM lms_attendance t1WHERe t1.id = (SELECt t2.id FROM lms_attendance t2 WHERe t2.user = t1.user ORDER BY t2.id DESC LIMIT 1)
