T-SQL:使用OVER和PARTITION BY

Question

我有以下数据

 |  Item  | Value |    Date   |
 ------------------------------
 |   1    |  10   | 01.01.2010
 |   1    |  20   | 02.01.2010
 |   1    |  30   | 03.01.2010
 |   1    |  40   | 04.01.2010
 |   1    |  50   | 05.01.2010
 |   1    |  80   | 10.01.2010
 |   2    |  30   | 04.01.2010
 |   2    |  60   | 06.01.2010
 |   2    |  70   | 07.01.2010
 |   2    |  80   | 08.01.2010
 |   2    |  100  | 09.01.2010

以下声明

SELECT   Item, Value, MIN(Date) OVER (PARTITION BY Item) 
FROM     Data
WHERE    Value >= 50   

我得到以下结果

 |  Item  | Value |    Date   |
 ------------------------------
 |   1    |  50   | 05.01.2010
 |   1    |  80   | 05.01.2010
 |   2    |  60   | 06.01.2010
 |   2    |  70   | 06.01.2010
 |   2    |  80   | 06.01.2010
 |   2    |  100  | 06.01.2010

但我需要的是这个

 |  Item  | Value |    Date   |
 ------------------------------
 |   1    |  10   | 05.01.2010
 |   1    |  20   | 05.01.2010
 |   1    |  30   | 05.01.2010
 |   1    |  40   | 05.01.2010
 |   1    |  50   | 05.01.2010
 |   1    |  80   | 05.01.2010
 |   2    |  30   | 06.01.2010
 |   2    |  60   | 06.01.2010
 |   2    |  70   | 06.01.2010
 |   2    |  80   | 06.01.2010
 |   2    |  100  | 06.01.2010

是否有任何快速的解决方案可以在没有自我加入的情况下使用一个法定单

谢谢 :)

Answer 1

如果没有自连接，请尝试以下操作：

DECLARE @YourTable table (item int,value int, Date datetime)
INSERT @YourTable VALUES (1    ,  10   , '01/01/2010')
INSERT @YourTable VALUES (1    ,  20   , '02/01/2010')
INSERT @YourTable VALUES (1    ,  30   , '03/01/2010')
INSERT @YourTable VALUES (1    ,  40   , '04/01/2010')
INSERT @YourTable VALUES (1    ,  50   , '05/01/2010')
INSERT @YourTable VALUES (1    ,  80   , '10/01/2010')
INSERT @YourTable VALUES (2    ,  30   , '04/01/2010')
INSERT @YourTable VALUES (2    ,  60   , '06/01/2010')
INSERT @YourTable VALUES (2    ,  70   , '07/01/2010')
INSERT @YourTable VALUES (2    ,  80   , '08/01/2010')
INSERT @YourTable VALUES (2    ,  100  , '09/01/2010')


SELECT   Item, Value, MIN(CASE WHEN Value >= 50 THEN Date ELSE NULL END) OVER (PARTITION BY Item) 
FROM     @YourTable

输出：

Item        Value       
----------- ----------- -----------------------
1           10          2010-05-01 00:00:00.000
1           20          2010-05-01 00:00:00.000
1           30          2010-05-01 00:00:00.000
1           40          2010-05-01 00:00:00.000
1           50          2010-05-01 00:00:00.000
1           80          2010-05-01 00:00:00.000
2           30          2010-06-01 00:00:00.000
2           60          2010-06-01 00:00:00.000
2           70          2010-06-01 00:00:00.000
2           80          2010-06-01 00:00:00.000
2           100         2010-06-01 00:00:00.000
Warning: Null value is eliminated by an aggregate or other SET operation.

(11 row(s) affected)