Question

我正在使用此代码:(来自这个问题：How to get the last record per group in SQL替换我自己的列）

WITH e AS
(
 SELECT *,
     ROW_NUMBER() OVER
     (
         PARTITION BY ApplicationId
         ORDER BY theDate DESC
     ) AS Recency
 FROM [Event]
)
SELECT *
FROM e
WHERE Recency = 1

仅当两个字段相同时才可以“分区”吗？例如，我有这样的数据：

ID      Name    theDate
123     John    01/01/2012
123     John    01/02/2012
123     Doe     01/01/2012
456     Smith   02/04/2012
789     Smith   02/01/2012
789     Smith   02/09/2012
789     Roger   02/08/2012

根据这些数据，我想回复：

ID      Name    theDate
123     John    01/02/2012
123     Doe     01/01/2012
456     Smith   02/04/2012
789     Smith   02/09/2012
789     Roger   02/08/2012

感谢您的帮助。

托马斯

Answer 1

您可以使用逗号分隔多个列

WITH e AS 
( 
 SELECT *, 
     ROW_NUMBER() OVER 
     ( 
         PARTITION BY ApplicationId , Name
         ORDER BY theDate DESC 
     ) AS Recency 
 FROM [Event] 
) 
SELECT * 
FROM e 
WHERE Recency = 1

Answer 2

我在这里找到答案：Table partitioning using 2 columns

您只能对1列进行分区，但是可以生成该列以创建“多个分区”，如下所示：

WITH e AS 
( 
 SELECT *, 
 ROW_NUMBER() OVER 
 ( 
     PARTITION BY CONVERT(VARCHAR(100),ApplicationId) + ' ' + Name
     ORDER BY theDate DESC 
 ) AS Recency 
 FROM [Event] 
) 
SELECT * 
FROM e 
WHERE Recency = 1

将两列作为一个单独的字符串添加在一起，确保只有在两列完全相同时才会进行分区。

是否可以仅在另一列也相同时使用ROW_NUMBER（）OVER / PARTITION BY？

2 个答案: