Question

我想在where子句中使用case语句，但在下面的查询中收到错误。

where 
 (r.WeekId=@WeekId or @WeekId is null) and
 (ShiftId=@ShiftId or @ShiftId is null)
 and (placeid=@PlaceId or @PlaceId is null)
 and (r.StatusId=3)
 AND     
CASE WHEN @day = 1 THEN ((firstday=@time and (allocateddays is null or NOT (AllocatedDays  LIKE '%1%')))) 
 WHEN @day = 2 THEN ((secondday=@time and (allocateddays is null or NOT (AllocatedDays LIKE '%2%'))))  
 WHEN @day = 3 THEN ((thirdday=@time  and (allocateddays is null or NOT (AllocatedDays LIKE '%3%')))) 
 ELSE AND (1 = 1) 
END

我在第CASE WHEN @day = 1行的Case语句中收到错误。我的查询出了什么问题。请帮忙。

Answer 1

CASE应该被重写为OR链，每个链都使用@day = n作为其中一个条件，因为它CASE已被指示返回一个值。它不能在WHERE子句中有条件地执行。

如果@day = 1之类的条件返回TRUE，则它将作为布尔AND与语句的其余部分一起使用。其中每个都通过OR链接到上一个。

where 
 (r.WeekId=@WeekId or @WeekId is null) and
 (ShiftId=@ShiftId or @ShiftId is null)
 and (placeid=@PlaceId or @PlaceId is null)
 and (r.StatusId=3)
 /* I *think* I have the () groups correct here... There's an unnecessary double (()) around firstday|secondday|thirddad */
 AND (
   (@day = 1 AND ((firstday=@time and (allocateddays is null or NOT (AllocatedDays  LIKE '%1%')))))
   OR (@day = 2 AND ((secondday=@time and (allocateddays is null or NOT (AllocatedDays LIKE '%2%')))))
   OR (@day = 3 AND ((thirdday=@time  and (allocateddays is null or NOT (AllocatedDays LIKE '%3%')))))
   /* Not certain if this is necessary in your case, as a catch-all to replace your ELSE */
   OR (@day NOT IN (1,2,3) AND 1=1) 
 )

Answer 2

在WHERE子句中，CASE语句只能用于为比较指定替代值，如下所示：

where @day = 
    case @SomeCondition
        when 1 then @Sunday
        when 2 then @Monday
        ...
    end

Answer 3

你不能让ELSE AND...没有编译器会处理它（除了像Fortran这样的语言）。

Answer 4

有一件事是错误的，即where子句中的CASE语句是赋值。例如，当您执行firstdaay=@time时。你不能这样做。您只能将表达式放在评估为true或false的where子句中，仅此而已。因此，你的整个where子句是错误的，坦率地说，对我来说没有多大意义。

where子句中的那些条件似乎更多地属于select子句：

select ... 
case when @day=1  and (allocateddays is null or NOT (AllocatedDays  LIKE '%1%') then firstday=@time else null end as first_day,
case when @day=2 and (allocateddays is null or NOT (AllocatedDays LIKE '%2%') then secondday=@time else null end as second_day

from ...

Answer 5

该行： ELSE和（1 = 1）看起来很可疑。拿出来尝试。

在sql server 2005中'='附近的语法不正确。在Where子句中的case语句中出错

5 个答案: