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

问题:

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!

回答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

回答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

回答3:

A little late but I can't be the only one bumping into this.

A solution could be to create a temporary table like this:

-- If previous run of this query fails, the temp table will be deleted.
-- Selecting into creates the temp table which fails if it already exists
IF EXISTS(SELECT [name] FROM tempdb.sys.tables WHERE [name] like '#dtBalansOpgesteldGefilterd%') BEGIN
   DROP TABLE #temp
END;

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)

-- Followed by select statement as required
SELECT *
INTO #temp
FROM CTE

IF @awsome = 1
BEGIN
    SELECT 'WHATEVERYOUWANT' AS WhateverColumnNameYouWant, *
    FROM #temp
END

回答4:

Try putting the CTE in the IF. It worked for me.

IF @awsome = 1 BEGIN ;WITH CTE AS ( SELECT * FROM SOMETABLE ) SELECT 'WHATEVERYOUWANT' FROM CTE END ELSE IF @awesome = 2 BEGIN ;WITH CTE2 AS ( SELECT * FROM SOMETABLE ) SELECT 'WHATEVERYOUWANT' FROM CTE2 END