where 子句中的 case 语句 - SQL Server [英] case statement in where clause - SQL Server

问题描述

我正在尝试在 SQL 查询的 where 子句中添加 case 或 if 语句.
我有一个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地点.这是我到目前为止所拥有的，但我收到了不正确的语法错误:

I'm trying to add a case or if statement in the where clause of my SQL query.
I have a table of journey times with a start and end date, and a boolean field for each day to signify where the journey happens on that day. Here is what I have so far, but I'm getting incorrect syntax errors:

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 

推荐答案

where 语句中不需要case，只需使用括号和或:

You don't need case in the where statement, just use parentheses and 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，您的语法对于案例是错误的.它不会向字符串追加内容——它返回单个值.如果您真的要使用 case 语句(您不应该这样做)，您会想要这样的东西:

Additionally, your syntax is wrong for a case. It doesn't append things to the string--it returns a single value. You'd want something like this, if you were actually going to use a case statement (which you shouldn't):

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 

另外，您可以使用 between 运算符作为您的日期:

And just for an extra umph, you can use the between operator for your date:

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
    )

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