查询中存在IF条件时CTE不起作用

Question

I am trying to add functionality on my query to select which query will be executed on a certain condition.

DECLARE @Test VARCHAR(50)
    SET @Test = 'A'

;WITH A AS (
  Select 'A is Selected' as SELECTED),
      B AS (
  Select 'B is Selected' as SELECTED)

IF(@Test = 'A')
  select * from A

IF(@Test <> 'A')
  select * from B

As of my Sample Test code above i got:

Msg 319, Level 15, State 1, Line 5
Incorrect syntax near the keyword 'with'. If this statement is a common table expression or an xmlnamespaces clause, the previous statement must be terminated with a semicolon.

Msg 102, Level 15, State 1, Line 8
Incorrect syntax near ','.

Maybe I'm missing something?

Answer 1

From WITH common_table_expression (Transact-SQL) .

defined within the execution scope of a single SELECT, INSERT, UPDATE, or DELETE statement.

I guess you want something like this.

declare @Test varchar(50);
set @Test='A';

with A as
(
  select 'A is Selected' as SELECTED
),
B as
(
  select 'B is Selected' as SELECTED
)
select *
from A
where @Test = 'A'    
union all
select *
from B
where @Test = 'B';

Answer 2

It seems to me that you should simply put both queries inside an IF statement as follows:

IF (@Test = 'A')
  select * from A
ELSE
  select * from B