按相同列中的值更新空值

Question

我在MS SQL Server中有一个表,其中"value"列中有一些空值

Group   ID    Value
A       1     10
A       2     
A       3     
A       4     40
B       1     
B       2     20
B       3     30
B       4          

我想在具有第一个更高ID的同一组中更新空值,而不是null,或者如果同一组中没有任何更高,则先降低.所以结果应该是这样的.

Group   ID    Value
A       1     10
A       2     40
A       3     40
A       4     40
B       1     20
B       2     20
B       3     30
B       4     30 

谢谢!

Answer 1

您可以使用窗口版本的SUM函数来确定NULL有价值记录的孤岛以及同一组中具有较高ID的记录:

SELECT [Group], ID, Value, 
       SUM(CASE WHEN Value IS NULL THEN 0 ELSE 1 END) OVER 
       (PARTITION BY [Group] ORDER BY ID DESC) AS grp
FROM mytable

输出:

Group   ID  Value   grp
-----------------------
A       4   40      1
A       3   30      2
A       2   NULL    2
A       1   NULL    2
B       4   40      1
B       3   NULL    1
B       2   20      2
B       1   10      3

您现在可以将上述查询包装在一个CTE并使用另一个查询进行CTE更新:

;WITH CTE AS (
SELECT [Group], ID, Value, 
       SUM(CASE WHEN Value IS NULL THEN 0 ELSE 1 END) OVER 
       (PARTITION BY [Group] ORDER BY ID DESC) AS grp
FROM mytable
), ToUpdate AS (
   SELECT [Group], ID, Value,  
          MAX(Value) OVER (PARTITION BY [Group], grp) AS group_value  
   FROM CTE
)
UPDATE ToUpdate
SET Value = group_value
WHERE Value IS NULL

在这里演示

编辑:

上面的查询不处理切片中最后一条记录的边缘情况.要处理这种情况,您可以使用以下查询:GroupNULL

;WITH CTE AS (
SELECT [Group], ID, Value, 
       SUM(CASE WHEN Value IS NULL THEN 0 ELSE 1 END) OVER 
       (PARTITION BY [Group] ORDER BY ID DESC) AS grp,
       SUM(CASE WHEN Value IS NULL THEN 0 ELSE 1 END) OVER 
       (PARTITION BY [Group] ORDER BY ID) AS grp2
FROM mytable
), ToUpdate AS (
   SELECT [Group], ID, Value,            
          MAX(Value) OVER (PARTITION BY [Group], grp) AS group_value,  
          MAX(Value) OVER (PARTITION BY [Group], grp2) AS group_value2  
   FROM CTE
)
UPDATE ToUpdate
SET Value = COALESCE(group_value, group_value2)
WHERE Value IS NULL

在这里演示

Answer 2

请试试这个 -

数据生成

DECLARE @T TABLE
(
    GroupCd CHAR(1),
    Id INT,
    Value INT
)

INSERT INTO @T
VALUES('A',1,10),
('A',2,NULL),
('A',3,NULL),
('A',4,40),
('B',1,NULL),
('B',2,20),
('B',3,30),
('B',4,NULL)

解

UPDATE a
SET a.Value = b.Value
FROM @T a
INNER JOIN 
( 
    SELECT a.GroupCd,a.Id,Coalesce(a.Value,z.Value,z1.Value) Value 
    FROM @T a
    OUTER APPLY 
    (
        SELECT TOP 1 Value
        FROM @T b
        WHERE a.GroupCd = b.GroupCd
        AND b.Value IS NOT NULL AND a.Id < b.Id
        ORDER BY Id 
    )z
    OUTER APPLY 
    (
        SELECT TOP 1 Value
        FROM @T b
        WHERE a.GroupCd = b.GroupCd
        AND b.Value IS NOT NULL AND a.Id > b.Id
        ORDER BY Id DESC
    )z1
)b ON a.GroupCd = b.GroupCd AND a.Id = b.Id

SELECT * FROM @T

OUTPUT

GroupCd Id          Value
------- ----------- -----------
A       1           10
A       2           40
A       3           40
A       4           40
B       1           20
B       2           20
B       3           30
B       4           30

(8 rows affected)