CTE之后的IF声明

Question

今天，我遇到了与IF语句有关的怪异问题。完成替换/创建CTE之后，在CTE之后有IF语句，并不断出现以下错误：

'if'附近的语法不正确

查询：

-- Other CTE's above.
CTE6 AS 
(
    SELECT
        -- Multiple Columns
    FROM
        table1
)
-- When the Query runs, I'd like it to use the correct IF BLOCK.

-- Error starts here.
if @param_policy = '1' 
    select * from CTE4
    where mid not in (select distinct mid from CTE6)
        and [CN] = @param_policy

if @param_policy = '2' 
    select * from CTE4 
    where mid not in (select distinct mid from CTE6)
        and [CN] = @param_policy

if @param_policy = '3' 
    select * from CTE4 
    where mid not in (select distinct mid from CTE6)
        and [CN] = @param_policy                

if @param_policy = '4' 
    select * from CTE4 
    where mid not in (select distinct mid from CTE6)
        and [CN] = @param_policy   
-- UPDATED

select * from CTE4 WHERE @param_policy = 'batch' and mid not in (select distinct mid from CTE6)

and not
(([Client Number] ='5' and  Pnum = 'IN' )
or ([Client Number] ='6' and  Pnum = 'G')
or [Client Number] in ('7' , '8', '9')
)

另外要包括的是，这样做select * from CTE4时会考虑CTE4无效，并且也不会将“ mid”识别为有效列。

我的CTE以前是临时表。

有人知道怎么修这个东西吗？

谢谢。

Answer 1

您可以执行以下操作：

select *
from CTE4
where @param_policy in ('1', '2', '3', '4')  and
      mid not in (select distinct mid from CTE6) and
      [CN] = @param_policy;

IF是T-SQL代码的控制流。它不是SELECT查询语法的一部分。

更一般而言，您可以使用以下方法进行操作union all：

select *
from CTE4
where @param_policy in ('1', '2', '3', '4')  and
      mid not in (select distinct mid from CTE6) and
      [CN] = @param_policy
union all
select *
from CTE4 
where @param_policy = 'batch' and
      mid not in (select distinct mid from CTE6) and
      not (([Client Number] ='5' and  Pnum = 'IN' ) or
           ([Client Number] ='6' and  Pnum = 'G') or
           ([Client Number] in ('7' , '8', '9')
          );

您也可以将这些条件添加到单个查询中，但是我认为这union all是您正在寻找的更通用的方法。

编辑：

或者，仅在中使用更复杂的逻辑WHERE：

select *
from CTE4
where mid not in (select distinct mid from CTE6) and
      ( (@param_policy in ('1', '2', '3', '4')  and
         [CN] = @param_policy
         ) or
         (@param_policy = 'batch' and
          not (([Client Number] ='5' and  Pnum = 'IN' ) or
               ([Client Number] ='6' and  Pnum = 'G') or
               ([Client Number] in ('7' , '8', '9')
              )
         )
      )