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。
我有一张包含开始和结束日期的旅程时间表，以及每天的布尔字段来表示当天旅程发生的位置。这是我目前所拥有的，但我遇到了不正确的语法错误：

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

where 语句中不需要case，只需使用括号和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，您的语法对于一个案例是错误的。它不会将内容附加到字符串 - 它返回单个值。如果您实际上要使用 case 语句（您不应该这样做），您会想要这样的东西：

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 

您可以使用between 运算符作为您的日期：

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

只需执行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))

Answer 3

CASE 语句是一个表达式，就像一个布尔比较。这意味着“AND”需要放在“CASE”语句之前，而不是在其中。：

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date)

AND -- Added the "AND" here

CASE WHEN @day = 'Monday' THEN (Monday = 1)   -- Removed "AND" 
    WHEN @day = 'Tuesday' THEN (Tuesday = 1)  -- Removed "AND" 
    ELSE AND (Wednesday = 1) 
END