where子句中的case语句 - SQL Server

Question

我正在尝试在我的SQL查询的where子句中添加case或if语句.
我有一个旅程时间表,包含开始和结束日期,每天都有一个布尔字段表示当天的旅程.这是我到目前为止,但我得到不正确的语法错误:

declare @date datetime
set @Date = '05/04/2012' 
declare @day nvarchar(50)
set @day = 'Monday'

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date)
CASE WHEN @day = 'Monday' THEN
 AND (Monday = 1)
WHEN @day = 'Tuesday' THEN
AND (Tuesday = 1)
ELSE
AND (Wednesday = 1) 
END 

Answer 1

您case在where声明中不需要使用括号和or:

Select * From Times
WHERE StartDate <= @Date AND EndDate >= @Date
AND (
    (@day = 'Monday' AND Monday = 1)
    OR (@day = 'Tuesday' AND Tuesday = 1)
    OR Wednesday = 1
)

此外,您的语法错误的情况.它不会向字符串附加内容 - 它返回单个值.你想要这样的东西,如果你真的要使用一个case声明(你不应该):

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date)
AND 1 = CASE WHEN @day = 'Monday' THEN Monday
             WHEN @day = 'Tuesday' THEN Tuesday
             ELSE Wednesday
        END 

只是为了额外的umph,您可以使用between运营商为您的日期:

where @Date between StartDate and EndDate

进行最终查询:

select
    * 
from 
    Times
where
    @Date between StartDate and EndDate
    and (
        (@day = 'Monday' and Monday = 1)
        or (@day = 'Tuesday' and Tuesday = 1)
        or Wednesday = 1
    )

Answer 2

只需做 select:

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date) AND
((@day = 'Monday' AND (Monday = 1))
OR (@day = 'Tuesday' AND (Tuesday = 1))
OR (Wednesday = 1))