--> 测试数据：[tb]
IF OBJECT_ID('[tb]') IS NOT NULL DROP TABLE [tb]
GO 
CREATE TABLE [tb]([SMT_id] INT,[dyid] INT,[SMT_data] DATETIME)
INSERT [tb]
SELECT 1,9,'2012-4-12 14:33:36' UNION ALL
SELECT 2,11,'2012-4-18 19:23:36' UNION ALL
SELECT 3,9,'2012-4-12 14:33:36' UNION ALL
SELECT 4,9,'2012-4-12 14:33:36' UNION ALL
SELECT 5,12,'2012-5-19 19:23:36' UNION ALL
SELECT 6,11,'2012-3-17 19:23:36'
--------------开始查询--------------------------
--1
SELECT * FROM [tb] t WHERE NOT EXISTS(SELECT 1 FROM [tb] WHERE [SMT_data]=t.[SMT_data] AND [SMT_id]>t.[SMT_id])
AND NOT EXISTS(SELECT 1 FROM [tb] WHERE [dyid]=t.[dyid] AND [SMT_data]>t.[SMT_data])
--2
SELECT * FROM [tb] t WHERE [SMT_id]=(SELECT MAX([SMT_id]) FROM [tb] WHERE [SMT_data]=t.[SMT_data])
AND [SMT_data]=(SELECT MAX([SMT_data]) FROM [tb] WHERE [dyid]=t.[dyid])
----------------结果----------------------------

/* 
SMT_id      dyid        SMT_data
----------- ----------- -----------------------
2           11          2012-04-18 19:23:36.000
4           9           2012-04-12 14:33:36.000
5           12          2012-05-19 19:23:36.000

(3 行受影响)


*/

------解决方案--------------------

探讨


本人是菜鸟，看不懂这个意思：WHERE [SMT_data]=t.[SMT_data]   这是同一个标里的字段做比较？


------解决方案--------------------

Select MAX(T1.SMT_id) As SMT_id , T1.dyid, T1.SMT_data
From @Tb T1 , (Select dyid, MAX(SMT_data) As SMT_data From @Tb
Group By dyid) T2  
Where (T1.dyid = T2.dyid And T1.SMT_data = T2.SMT_data)
Group By  T1.dyid, T1.SMT_data
Order By T1.SMT_data Desc