如何在SQL的Where子句中使用If语句？

Question

我需要在sql中的where子句中使用if语句.

Select * from Customer
WHERE  (I.IsClose=@ISClose OR @ISClose is NULL)  
AND    
(C.FirstName like '%'+@ClientName+'%' or @ClientName is NULL )    
AND 
 if (@Value=2)
  begin
  (I.RecurringCharge=@Total  or @Total is NULL )    
  end
 else if(@Value=3)
begin
(I.RecurringCharge like '%'+cast(@Total as varchar(50))+'%' or @Total is NULL )  
end

注意:这不是完整的代码.所有内容都在SP中定义.我只需编写理解该问题所需的代码.

提前致谢.

Answer 1

SELECT *
  FROM Customer
 WHERE (I.IsClose=@ISClose OR @ISClose is NULL)  
   AND (C.FirstName like '%'+@ClientName+'%' or @ClientName is NULL )    
   AND (isnull(@Value,1) <> 2
        OR I.RecurringCharge = @Total
        OR @Total is NULL )    
   AND (isnull(@Value,2) <> 3
        OR I.RecurringCharge like '%'+cast(@Total as varchar(50))+'%'
        OR @Total is NULL )

基本上,你的病情是

if (@Value=2)
   TEST FOR => (I.RecurringCharge=@Total  or @Total is NULL )    

翻了个身,

AND (isnull(@Value,1) <> 2                -- A
        OR I.RecurringCharge = @Total    -- B
        OR @Total is NULL )              -- C

当(A)为真时,即@Value 不是 2,无论B和C结果如何,[A或B或C]都将变为TRUE.B和C实际上只在检查时才会检查@Value = 2,这是初衷.

Answer 2

您必须使用CASE Statement/Expression

Select * from Customer
WHERE  (I.IsClose=@ISClose OR @ISClose is NULL)  
AND    
    (C.FirstName like '%'+@ClientName+'%' or @ClientName is NULL )    
AND 
     CASE @Value
         WHEN 2 THEN (CASE I.RecurringCharge WHEN @Total or @Total is NULL) 
         WHEN 3 THEN (CASE WHEN I.RecurringCharge like 
                               '%'+cast(@Total as varchar(50))+'%' 
                     or @Total is NULL )
     END