Thread: Referencing function value inside CASE..WHEN

You can try using a CTE/With clause.  Failing that use a function with SELECT INTO...

On Jun 18, 2011, at 22:45, lover boi <lover-boi@live.co.uk> wrote:

> Hi,
>
> In the following statement, does the custom function get executed twice?
>
> SELECT
>   MY_FUNCTION(...),
>   CASE WHEN MY_FUNCTION(...) = '...' THEN '...' ELSE '...' END
> ...
> ...
>
>
> If so, is there a way I can make it execute once?  I tried this but it gave me a "Column my_function does not exist"
error.
>
> SELECT
>
>   MY_FUNCTION(...) AS my_function,
>
>   CASE WHEN my_function = '...' THEN '...' ELSE '...' END
>
> ...
>
> ...
>
>
> Thank you in advance.

Hello

2011/6/19 lover boi <lover-boi@live.co.uk>:
> Hi,
>
> In the following statement, does the custom function get executed twice?
>
> SELECT
>   MY_FUNCTION(...),
>   CASE WHEN MY_FUNCTION(...) = '...' THEN '...' ELSE '...' END
> ...
> ...
>
>
> If so, is there a way I can make it execute once?  I tried this but it gave
> me a "Column my_function does not exist" error.
>

SELECT x, CASE WHEN x THEN .. ELSE .. END FROM (SELECT fce(..) x FROM foo) s;

Regards

Pavel Stehule

> SELECT
>
>   MY_FUNCTION(...) AS my_function,
>
>   CASE WHEN my_function = '...' THEN '...' ELSE '...' END
>
> ...
>
> ...
>
>
> Thank you in advance.

On Sun, Jun 19, 2011 at 10:45:12AM +0800, lover boi wrote:
> In the following statement, does the custom function get executed twice?
>
> SELECT
>   MY_FUNCTION(...),
>   CASE WHEN MY_FUNCTION(...) = '...' THEN '...' ELSE '...' END

Yes

> If so, is there a way I can make it execute once?  I tried this but it gave me a "Column my_function does not exist"
error.
>
> SELECT
>
>   MY_FUNCTION(...) AS my_function,
>
>   CASE WHEN my_function = '...' THEN '...' ELSE '...' END

You almost had it right, there is another syntax for CASE:

CASE MY_FUNCTION(...) WHEN 'foo' THEN ... WHEN 'bar' THEN ... ELSE ... END;

http://www.postgresql.org/docs/8.4/static/functions-conditional.html

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patriotism is when love of your own people comes first; nationalism,
> when hate for people other than your own comes first.
>                                       - Charles de Gaulle