Question

我试图在SQL Server 2005中的select语句中使用case语句，并且我得到错误“当子查询未引入EXISTS时，只能在选择列表中指定一个表达式。”不能在SQL查询中使用一个案例？！

declare @TypeofDayID int
set @TypeofDayID = (Select TypeofDayID from RepInfo where RepInfoID = @RepInfoID)


Select CASE 
    WHEN @TypeofDayID = 1 
        THEN (Select * from RepInfo RD inner join SellingInfo S on S.RepInfoID = @RepInfoID)
    WHEN @TypeofDayID = 2
        THEN (Select * from RepInfo RD inner join UpgradingInfo U on U.RepInfoID = @RepDailyID)
    WHEN @TypeofDayID = 9 or @TypeofDayID = 10
        THEN (Select * from RepInfo RD inner join DeliveryInfo D on D.RepDailyID = @RepDailyID)
    END
from RepInfo RD

Answer 1

CASE未用于逻辑流控制...请改用IF / ELSE IF：

declare @TypeofDayID int
set @TypeofDayID = (Select TypeofDayID from RepInfo where RepInfoID = @RepInfoID)

IF @TypeofDayID = 1 
  Select * 
  from RepInfo RD inner join SellingInfo S on S.RepInfoID = @RepInfoID
ELSE IF @TypeofDayID = 2
  Select * 
  from RepInfo RD inner join UpgradingInfo U on U.RepInfoID = @RepDailyID
ELSE IF @TypeofDayID = 9 or @TypeofDayID = 10
  Select * 
  from RepInfo RD inner join DeliveryInfo D on D.RepDailyID = @RepDailyID

请记住......由于您使用的是SELECT *，并且根据@TypeOfDayID加入了不同的表格，您可能会得到锯齿状的结果集，这意味着您根据采取的分支，将有不同数量的列。

以编程方式处理这可能会很麻烦，因此出于这个原因避免使用SELECT *是个好主意，以及其他原因......

Answer 2

我认为你想要做的事情可以通过这种方式得到更好的处理。

declare @TypeofDayID int
set @TypeofDayID = (Select TypeofDayID from RepInfo where RepInfoID = @RepInfoID)

IF @TypeofDayID = 1 
    Select * 
    from RepInfo RD 
    inner join SellingInfo S on S.RepInfoID = @RepInfoID
ELSE IF @TypeofDayID = 2
    Select * 
    from RepInfo RD 
    inner join UpgradingInfo U on U.RepInfoID = @RepDailyID
ELSE IF @TypeofDayID = 9 or @TypeofDayID = 10
    Select * 
    from RepInfo RD 
    inner join DeliveryInfo D on D.RepDailyID = @RepDailyID

SQL查询中的Case语句

2 个答案: