sql-server – 如何在UPDATE子句中使用ROW_NUMBER()？

参见英文答案 > SQL Update with row_number()
ROW_NUMBER()仅用于MS SQL Server中的SELECT子句，但是我想将其用于如下更新：

Update MyTab Set MyNo = 123 +  ROW_NUMBER() over (Order By ID)
Where a=b;

那我就得错了，

Windowed functions can only appear in the SELECT or ORDER BY clauses.

如何在UPDATE子句中使用ROW_NUMBER()？

解决方法

DECLARE @MyTable TABLE
(
    ID INT IDENTITY(2,2) PRIMARY KEY,MyNum INT,ColA INT,ColB INT
);

INSERT  @MyTable (ColA,ColB)
SELECT 11,11 UNION ALL
SELECT 22,22 UNION ALL
SELECT NULL,NULL UNION ALL
SELECT 33,NULL UNION ALL
SELECT NULL,44 UNION ALL
SELECT 55,66;

UPDATE  UpdateTarget
SET     MyNum = RowNum
FROM
(
    SELECT  x.MyNum,ROW_NUMBER() OVER(ORDER BY x.ID) AS RowNum
    FROM    @MyTable x
    WHERE   x.ColA = x.ColB
) AS UpdateTarget;

SELECT * FROM @MyTable;

结果：

ID          MyNum       ColA        ColB
----------- ----------- ----------- -----------
2           1           11          11
4           2           22          22
6           NULL        NULL        NULL
8           NULL        33          NULL
10          NULL        NULL        44
12          NULL        55          66