从最大查询

Question

选择列名我有一个查询是这样的：

;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，但我想知道的是马克斯（金额）的由来。 （RowNumber，ObjectId，Amount）我想要列（Col1，Col2，Col3，Col4）的名称作为字符串。

有没有办法做到这一点？

编辑 问题来自评论：如果两列有相同的最大值，它可能是一个？是的，它可以是任何一个。只要我知道它可能来自哪里，任何列名都会执行。

使用SQL Server 2008

Answer 1

一个步骤中，您可以使用UNPIVOT和OUTER APPLY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 

Answer 2

不要MAX：使用TOP避免聚合/ GROUP BY。

它还可以处理使用WITH TIES重复

我不知道，如果你遇到了什么是伪代码或者一个子查询，但这应该做你想做的

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 

你的主要问题是，无论你如何操作，你都必须触碰表格4次，因为子查询只返回一个值。我看不到ROW_NUMBER解决方案（但是可能有一个虽然... :-)

Answer 3

这是未经测试的：但是要查看您的数据正在发生什么，这可能有所帮助。不是真正的产品代码质量：

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。 你的SQL看起来很奇怪，你使用的是什么DBMS？

Answer 4

添加到user202553's answer

;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