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Using CTE Common table expressions with SELECT CASE statement

Hi, This gives me error.

DECLARE @r INT
SELECT @r = 1
;WITH sam AS (select * from test)
SELECT  1, CASE @r
            WHEN 1 THEN (SELECT * FROM sam)
            WHEN 2 THEN 200
            ELSE 0
        END

Msg 156, Level 15, State 1, Line 5
Incorrect syntax near the keyword 'SELECT'.

What I need is a way to run different CTE based on the condition. Something like this:

WITH CTE_1 AS (SELECT * FROM test1)
, CTE_2 AS (SELECT * FROM test2)
IF <condition A>
    SELECT FROM CTE_1
ELSE
    SELECT * FROM CTE_2

But since, CTE's must be followed by a SELECT, INSERT., etc statements only, I tried to use SELECT CASE statement, s given above.

How do I do this, other than defining CTE's twice.

thanks, _Ub

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asked Feb 27 '10 at 04:55 AM in Default

UB gravatar image

UB
37 2 2 2

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3 answers: sort voted first

What you're describing will actually change the shape of the resultset.

You could easily do it in a stored procedure using an IF statement. Otherwise, assuming your CTEs have the same columns, you could do something like:

WITH cte1 as ..., cte2 as ... SELECT * FROM cte1 WHERE <condition> UNION ALL SELECT * FROM cte2 WHERE <not condition> ; 
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answered Feb 27 '10 at 06:46 AM

Rob Farley gravatar image

Rob Farley
5.7k 15 18 20

The SQL query in both cases [IF and ELSE] returns the same number of columns and data types. I wanted to know if CTE's are accessible from If and ELSE locations. From BoL, CTE's must be followed by a SELECT, INSERT, etc.. statements only. So I re-wrote it using SELECT CASE statement. Where CASE 1 runs the first CTE CASE 2 runs the second CTE. But that is giving me error too.
Feb 27 '10 at 01:48 PM UB
You can't say ‘case when ... then (select ...)‘ with something that returns multiple columns. CASE must return a single value only.
Feb 27 '10 at 07:36 PM Rob Farley
Makes sense. I did not think of that. Thanks. I got around the problem in a different way thought. Thanks for your help.
Feb 28 '10 at 01:09 AM UB
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Is there a reason you cannot use multiple statements like so:

Declare @R int Set @R = 1

If @R = 1 With Sam As ( Select ... From Test ) Select ... From Sam

Else Select 200
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answered Feb 27 '10 at 10:43 PM

Thomas 1 gravatar image

Thomas 1
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The CASE expression has two formats:

Simple CASE Expression: compares an expression to a set of simple expressions to determine the result. Syntax CASE input_expression WHEN when_expression THEN result_expression [ ...n ] [ ELSE else_result_expression ] END Searched CASE Expression: evaluates a set of Boolean expressions to determine the result.

Syntax CASE WHEN Boolean_expression THEN result_expression [ ...n ] [ ELSE else_result_expression ] END

a good referance with example:http://cybarlab.blogspot.com/2013/02/sql-case-statementexpression.html

Hope it will help you.

Thanks n regard

1: http://cybarlab.blogspot.com/2013/02/sql-case-statementexpression.html, The CASE expression has two formats:

Simple CASE Expression: compares an expression to a set of simple expressions to determine the result. Syntax CASE input_expression WHEN when_expression THEN result_expression [ ...n ] [ ELSE else_result_expression ] END Searched CASE Expression: evaluates a set of Boolean expressions to determine the result.

Syntax CASE WHEN Boolean_expression THEN result_expression [ ...n ] [ ELSE else_result_expression ] END

a good referance with example:http://cybarlab.blogspot.com/2013/02/sql-case-statementexpression.html

Hope it will help you.

Thanks n regard

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answered Mar 27 '13 at 07:00 AM

cybarcom gravatar image

cybarcom
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asked: Feb 27 '10 at 04:55 AM

Seen: 5235 times

Last Updated: Mar 27 '13 at 07:00 AM