Question

我的SQL查询代码中需要支持。我必须用下一行的非空值替换一列中的空值。

作为示例，我们可以使用以下代码：

declare   @value table (r# int, value varchar(15))
insert into @value ( r#, value ) values
 (1, NULL   ) ,
 (2, 'January'), 
 (3, 'February' ), 
 (4, NULL    ),
 (5, 'March'  ),
 (6, NULL    ),
(7, Null  ),
(8, 'December' ),
(9, Null ),
(10, Null  ),
(11, Null  ),
(12, 'November' ),
(13, Null )
select * from @value

当我使用Lead函数时，会得到此值，但不适用于NULL。我需要得到的是：

1 January
2 January
3 February
4 March
5 March
6 December
7 December
8 December
9 November
10 November
11 November
12 November
13 NULL

我的查询中的Bu：

SELECT r#, 
  value
 ,case when value is null  then Lead(value) OVER ( order by  r#  asc) else value end as RESULT 
FROM @value
order by r#

我有：

Answer 1

下一种方法可能会有所帮助。您需要其他APPLY运算符才能找到第一个没有NULL值的记录：

T-SQL：

SELECT 
    v1.[r#], 
    CASE 
        WHEN v1.[value] IS NULL THEN v2.[value]
        ELSE v1.[value]
    END AS [value]
 FROM @value v1
 OUTER APPLY (
    SELECT TOP 1 [Value]
    FROM @value 
    WHERE (v1.[r#] < [r#]) AND [value] IS NOT NULL
) v2

输出：

r#  value
1   January
2   January
3   February
4   March
5   March
6   December
7   December
8   December
9   November
10  November
11  November
12  November
13  NULL

Answer 2

您可以使用窗口功能执行此操作。不幸的是，SQL Server不支持IGNORE NULL上的LEAD() s选项，因此这不是一个选项。

但是，您可以使用两个级别的窗口功能：

select v.r#, v.value,
       coalesce(v.value, max(value) over (partition by next_r#)) as imputed_value
from (select v.*,
             min(case when value is not null then r# end) over (order by r# desc) as next_r#
      from @value v
     ) v
order by v.r#;

在13行上，性能差异可能并不明显。但是，随着行数的增加，这应该具有更好的性能。

Answer 3

您可以使用相关子查询尝试以下sql代码

SELECT v1.r#,CASE WHEN value IS NOT NULL THEN v1.Value 

             ELSE ( SELECT TOP 1 value
                    FROM @value  v2
                    WHERE v2.r# > v1.r# AND v2.[value] IS NOT NULL
                  ) END  Value 
FROM @value v1

结果

r#  Value
----------
1   January
2   January
3   February
4   March
5   March
6   December
7   December
8   December
9   November
10  November
11  November
12  November
13  NULL

Answer 4

以下查询在SQL Server中有效：

;WITH CTE_Value
AS (
    SELECT R#, Value
    FROM @value AS T
    WHERE Value IS NOT NULL

    UNION ALL

    SELECT t.r#, c.Value
    FROM @value AS t
    INNER JOIN CTE_Value AS c ON t.r# + 1 = c.r#
    WHERE t.Value IS NULL
    )
SELECT *
FROM CTE_Value

UNION ALL

SELECT v.*
FROM @value AS v
LEFT JOIN CTE_value AS c ON v.r# = c.r#
WHERE c.r# IS NULL
ORDER BY r#

如何用下一行中的值替换空值

4 个答案: