Question

我有下面的查询，我正在寻找从另一个表中动态列名称标签。在表＃Tmp2中，Dim1根据Dim1.Num而变化，例如我可以拥有对于Dim1.Num = 1 => Dim1 =BusinessUnit
在其他cas我可以有Dim1.Num = 1 => Dim1 =Department

SELECT Dim1.Dim1 ,Dim1.ValueDim1  ,
       Dim2.Dim2 ,Dim2.ValueDim2  ,
       #Tmp1.Amount

INTO   #Tmp3

FROM   #Tmp1

INNER JOIN #Tmp2 as Dim1 on Dim1.id = #Tmp1.id And Dim1.Num=1
INNER JOIN #Tmp2 as Dim2 on Dim1.id = #Tmp1.id And Dim2.Num=2

结果如下：

Dim1            ValueDim1  Dim2         ValueDim2  Amount
BusinessUnit    002        Department   027        1000

但我想要这个结果

BusinessUnit    ValueDim1  Department   ValueDim2  Amount
BusinessUnit    002        Department   027        1000

也就是说，根据#Tmp2.Num的值，可以更改列的适用名称。

mybe像这样的事情

SELECT Dim1.Dim1 AS (select Dim from #Tmp2 where #Tmp2.Num = 1)

Answer 1

您可以使用动态SQL：

DECLARE @ColName VARCHAR(20) = (select Dim from #Tmp2 where #Tmp2.Num = 1)

EXEC('SELECT Dim1.Dim1 ['+@ColName+'] ,Dim1.ValueDim1  ,
       Dim2.Dim2 ,Dim2.ValueDim2  ,
       #Tmp1.Amount

INTO   #Tmp3

FROM   #Tmp1

INNER JOIN #Tmp2 as Dim1 on Dim1.id = #Tmp1.id And Dim1.Num=1
INNER JOIN #Tmp2 as Dim2 on Dim1.id = #Tmp1.id And Dim2.Num=2')

此限制（以及您的一般问题）是，如果您的#Tmp2有两条记录具有相同的Num，则查询将抛出Subquery returned more than one value错误。解决这个问题的唯一方法是更改@ColName查询，使其只返回一个值：

DECLARE @ColName VARCHAR(20) = (select TOP 1 Dim from #Tmp2 where #Tmp2.Num = 1)

<强>更新

如果获取列名的查询可能返回0条记录，则按如下方式修改查询：

DECLARE @ColName VARCHAR(20) = (
    select Dim from #Tmp2 where #Tmp2.Num = 1 
    UNION 
    SELECT 'DefaultValue' WHERE NOT EXISTS (select Dim from #Tmp2 where #Tmp2.Num = 1)
    )

但是，如果您的查询返回一条记录，但您要用作列名的列中的值为null，则修改查询，如下所示：

DECLARE @ColName VARCHAR(20) = (select ISNULL(Dim,'DefaultValue') from #Tmp2 where #Tmp2.Num = 1)

如何从另一个表动态化列别名

1 个答案: