如何将列结果分配给查询的参数

Question

我有一个表“ Values”，数据看起来像这样：

    ID     Label     Value

    1     StartDate  1/1/17
    2     EndDate    1/15/17
    3     Dept         6

我想做的是将“标签”列的值加载到查询中的相应参数中：

    Declare 
    @startdate Datetime,
    @enddate Datetime,
    @DepartmentID int

Select * 
From Customers 
Where created between @startdate and @enddate and @DepartmentID

如何在值表中将@Startdate分配给'Startdate''value'？ 另外，由于我在查询中使用的数据类型不同，因此与值表中存储的数据类型不同（值在值表中为“ nvarchar”），我是否会遇到潜在的问题？

Answer 1

您可以尝试执行以下操作：

SELECT 
    * 
FROM 
    CUSTOMERS
WHERE
    CREATED BETWEEN 
        (SELECT TOP 1 [Value] FROM Values WHERE Label = 'StartDate') --perform casts here if necessary
        AND
        (SELECT TOP 1 [Value] FROM Values WHERE Label = 'EndDate')   --perform casts here if necessary

Answer 2

Declare 
@startdate Datetime,
@enddate Datetime,
@DepartmentID int

set @startdate = (Select convert(datetime,[Value]) from dbo.Values where Label='StartDate')
set @enddate = (Select convert(datetime,[Value]) from dbo.Values where Label='EndDate')
set @DepartmentID =(Select convert(int,[Value]) from dbo.Values where Label='Dept')

Select * 
From Customers 
Where created between @startdate and @enddate and DepartmentId = @DepartmentID