如何选择具有最大日期的行

Question

这是我的表名 tblPE

PEID |idnum  | PE_DATE_EXAM   | ATTENDANCE       
1    | 39    | 2014-08-01     | PRESENT       
2    | 42    | 2014-08-10     | ABSENT            
3    | 39    | 2014-08-12     | PRESENT           
4    | 43    | 2014-08-05     | PRESENT        
5    | 42    | 2014-07-15     | NULL           
6    | 39    | 2014-07-03     | ABSENT       
7    | 41    | 2014-08-01     | PRESENT    

我想选择最大 PE_DATE_EXAM 值，其中 idnum = 39 且 ATTENDANCE=PReSENT

结果应该是：

PEID |idnum  | PE_DATE_EXAM   | ATTENDANCE
-------------------------------------------
3    | 39    | 2014-08-12     | PRESENT

Answer 1

对于单个记录返回，您可以使用LIMIT：

SELECT * FROM tblPE t
WHERE t.idnum = 39 AND t.ATTENDANCE = 'PRESENT'
ORDER BY t.PE_DATE_EXAM DESC
LIMIT 1;

如果你希望它对所有人都是动态的idnum，你可以使用NOT EXISTS()：

SELECT * FROM tblPE t
WHERE NOT EXISTS(SELECT 1 FROM tblPE s
                 WHERE t.idnum = s.idnum AND s.ATTENDANCE = 'PRESENT')
  AND t.attendance = 'PRESENT'