How can I use if statement after a CTE (SQL Server 2005)

Question

Last night I was writing a simple T-SQL program something like this

DECLARE @ROLEID AS INT

SELECT @ROLEID = [ROLE ID] FROM TBLROLE

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
IF (@ROLEID  = 1) 
BEGIN
      //SOMECODE
END
ELSE IF(@ROLEID  = 2) 
BEGIN
      //SOMECODE
END
ELSE
BEGIN 
      //SOMECODE
END

I found after compilation that it is throwing error something like "Incorrect statement near if"

What is wrong?

However, I did that by using some other way. But I wanted to know why it did not work!

Answer 1

Common table expressions are defined within the context of a single statement:

WITH cte_name AS (
  <cte definition>)
<statement that uses cte>;

So you can do something like:

WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
SELECT * FROM CTE;

or

WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
UPDATE CTE 
SET somefield = somevalue
WHERE id = somekey;

A CTE must be followed by a single SELECT, INSERT, UPDATE, MERGE, or DELETE statement that references some or all the CTE columns. A CTE can also be specified in a CREATE VIEW statement as part of the defining SELECT statement of the view

Answer 2

The closest you'll get is using a UNION ALL to do a crude switched select:

DECLARE @ROLEID AS INT

SELECT @ROLEID = [ROLE ID] FROM TBLROLE

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 1
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 2
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 3
...
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = n