从最大查询中选择列名

Question

我有一个类似这样的查询：

 ;WITH t as
(
select 1 as RowNumber, 1 as ObjectID, 10 as [Col1],  20 as [Col2],  20 as [Col3],  20 as [Col4] UNION ALL
select 2 as RowNumber, 2 as ObjectID, 20 as [Col1],  30 as [Col2],  40 as [Col3],  50 as [Col4]
)
SELECT  RowNumber, ObjectID,
        (
        SELECT  MAX(Amount)
        FROM    (
                SELECT  [Col1] AS Amount
                UNION ALL
                SELECT  [Col2]
                UNION ALL
                SELECT  [Col3]
                UNION ALL
                SELECT  [Col4]
                ) d
       WHERE   Amount > 0
        )
FROM    t

查询工作正常，但我想知道 Max(Amount) 来自哪里。

因此，在我的结果集中，除了具有 (RowNumber, ObjectId, Amount) 之外，我还希望将列的名称 (Col1, Col2, Col3, Col4) 作为字符串。

有什么办法吗？

编辑 cmets 的问题：如果两列具有相同的最大值，它可能是任何一个？是的，它可以是任何一个。只要我知道它可能来自哪里，任何列名都可以。

使用 SQL Server 2008

Answer 1

不要 MAX：使用 TOP 以避免聚合/GROUP BY。

它还可以使用 WITH TIES 处理重复项

我不确定您拥有的是伪代码还是子查询，但这应该可以满足您的需求

 SELECT TOP 1 -- WITH TIES if needed
     *
 FROM
     (
     SELECT  RowNumber, ObjectID, [Col1] AS Amount, 'Col1' AS ColName
     FROM table
     UNION ALL
     SELECT  RowNumber, ObjectID, [Col2], 'Col2' AS ColName
     FROM table
     UNION ALL
     SELECT  RowNumber, ObjectID, [Col3], 'Col3' AS ColName
     FROM table
     UNION ALL
     SELECT  RowNumber, ObjectID, [Col4], 'Col4' AS ColName
     FROM table
     ) foo
 WHERE   Amount > 0
 ORDER BY Amount DESC

您的主要问题是，无论您如何操作，您都必须触摸表格 4 次，因为子查询只返回一个值。我也看不到 ROW_NUMBER 解决方案（但可能有一个... :-)

Answer 2

这是未经测试的：但是要查看您的数据发生了什么，这可能会有所帮助。不是真正的生产代码质量：

SELECT  RowNumber, ObjectID,
        (
        SELECT  MAX(Amount)
        FROM    (
                SELECT str([Col1]) + ", col1, " AS Amount
                UNION ALL
                SELECT str([Col2]) + ", col2" 
                UNION ALL
                SELECT str([Col3]) + ", col3"
                UNION ALL
                SELECT str([Col4]) + ", col4"
                )
        WHERE   Amount > 0
        )
FROM    table

str() 是 DBMS 的“toString()”函数。 您的 SQL 看起来很奇怪，您使用的是什么 DBMS？

Answer 3

给user202553's answer添加一个步骤

;WITH t1 as(
select 1 as RowNumber, 1 as ObjectID, 10 as [Col1],  20 as [Col2],  20 as [Col3],  20 as [Col4] UNION ALL
select 2 as RowNumber, 2 as ObjectID, 20 as [Col1],  30 as [Col2],  40 as [Col3],  50000045 as [Col4]
),
t2 as(
SELECT  RowNumber, ObjectID,
        (
        SELECT  TOP 1 CAST(C AS BINARY(4)) + CAST(Amount as BINARY(4)) 
        FROM    (
                SELECT 'Col1' AS C, [Col1] AS Amount
                UNION ALL
                SELECT 'Col2' AS C, [Col2]
                UNION ALL
                SELECT 'Col3' AS C, [Col3]
                UNION ALL
                SELECT 'Col4' AS C, [Col4]
                ) d
       WHERE   Amount > 0
       ORDER BY Amount desc
        ) AS Top1
FROM    t1
)
SELECT RowNumber, 
       ObjectID,
       CAST(Left(Top1, 4) AS CHAR(4)) AS Col, 
       CAST(SUBSTRING(Top1,5,4) AS INT) AS Amount
FROM t2

Answer 4

您可以使用UNPIVOT 和OUTER APPLY 的组合：

;WITH t as     (
select 1 as RowNumber, 1 as ObjectID, 10 as [Col1],  20 as [Col2],  
       20 as [Col3],  20 as [Col4] UNION ALL
select 2 as RowNumber, 2 as ObjectID, 20 as [Col1],  30 as [Col2],  
       40 as [Col3],  50 as [Col4] )
SELECT 
  RowNumber,
  ObjectID,
  ColName,
  ColAmount
FROM t
OUTER APPLY (
  SELECT TOP 1 
    ColName,
    ColAmount
  FROM 
    (
      SELECT
        Col1,
        Col2,
        Col3,
        Col4
    ) x 
    UNPIVOT (
      ColAmount FOR ColName IN (Col1, Col2, Col3, Col4) 
    ) y
   WHERE ColAmount > 0
   ORDER BY ColAmount DESC
 ) z

结果：

RowNumber   ObjectID    ColName   ColAmount
----------- ----------- --------- -----------
1           1           Col2      20
2           2           Col4      50