sql - MSSQL 2008 中的行合并，

Question

我正在尝试确定 MSSQL 2008 中的最佳方法。

这是我的示例数据

TransDate  Id     Active
-------------------------
1/18 1pm   5      1    
1/18 2pm   5      0    
1/18 3pm   5      Null    
1/18 4pm   5      1    
1/18 5pm   5      0    
1/18 6pm   5      Null

如果按 Id 分组并按 TransDate 排序，我需要事件列的最后一个非空值以及 TransDate 的最大值

SELECT MAX(TransDate) AS TransDate, 
       Id,
       --LASTNonNull(Active) AS Active

结果如下:

TransDate  Id  Active
---------------------    
1/18 6pm   5   0

这就像合并，但在行上，而不是两个值/列。

还有许多其他列也会应用这种类似的方法，所以我真的不想为每个列进行单独的连接。

有什么想法吗？

Answer 1

我可能会使用相关子查询。

SELECT MAX(TransDate)             AS TransDate,
       Id,
       (SELECT TOP (1) Active
        FROM   T t2
        WHERE  t2.Id = t1.Id
               AND Active IS NOT NULL
        ORDER  BY TransDate DESC) AS Active
FROM   T t1
GROUP  BY Id  

没有的方法

SELECT
    Id,
    MAX(TransDate) AS TransDate,
    CAST(RIGHT(MAX(CONVERT(CHAR(23),TransDate,121) + CAST(Active AS CHAR(1))),1) AS BIT) AS Active,
    /*You can probably figure out a more efficient thing to 
    compare than the above depending on your data. e.g.*/
    CAST(MAX(DATEDIFF(SECOND,'19500101',TransDate) * CAST(10 AS BIGINT) + Active)%10  AS BIT) AS Active2
FROM T
GROUP BY Id

或者按照评论交叉应用对您来说效果更好？

WITH T (TransDate, Id, Active, SomeOtherColumn) AS
(
select GETDATE(), 5, 1, 'A' UNION ALL
select 1+GETDATE(), 5, 0, 'B' UNION ALL
select 2+GETDATE(), 5, null, 'C' UNION ALL
select 3+GETDATE(), 5, 1, 'D' UNION ALL
select 4+GETDATE(), 5, 0, 'E' UNION ALL
select 5+GETDATE(), 5, null,'F'

),
T1 AS
(
SELECT MAX(TransDate) AS TransDate,
       Id
FROM   T
GROUP  BY Id  
)
SELECT T1.TransDate,
       Id,
       CA.Active AS Active,
       CA.SomeOtherColumn AS SomeOtherColumn
FROM   T1
CROSS APPLY (SELECT TOP (1) Active, SomeOtherColumn
        FROM   T t2
        WHERE  t2.Id = T1.Id
               AND Active IS NOT NULL
        ORDER  BY TransDate DESC) CA