如何將列結果分配給查詢的參數

Question

我有一個表“ Values”，數據看起來像這樣：

    ID     Label     Value

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

我想做的是將“標簽”列的值加載到查詢中的相應參數中：

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

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

如何在值表中將@Startdate分配給'Startdate''value'？ 另外，由於我在查詢中使用的數據類型不同，因此與值表中存儲的數據類型不同（值在值表中為“ nvarchar”），我是否會遇到潛在的問題？

Answer 1

您可以嘗試執行以下操作：

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