Thread: CASE

Hi everyone, I'm trying to figure out how to get CASE working in a sum
aggregate function.  Pretty simple query:

select sum(numbers) from lists where uid=1;

It's possible that there may be 0 rows where uid == 1.  Instead of
returning 1 blank row, I want it to return '0'.  So, I tried this:

select case(sum(numbers)) when null then 0 else sum(numbers) end from
list_results;

That... Doesn't work.  Any suggestions on how to do this and where I can
find some decent information on use of CASE?

On Sun, 18 May 2003, James Taylor wrote:

> Hi everyone, I'm trying to figure out how to get CASE working in a sum
> aggregate function.  Pretty simple query:
>
> select sum(numbers) from lists where uid=1;
>
> It's possible that there may be 0 rows where uid == 1.  Instead of
> returning 1 blank row, I want it to return '0'.  So, I tried this:
>
> select case(sum(numbers)) when null then 0 else sum(numbers) end from
> list_results;

I believe the case would be:

case when sum(numbers) is null then 0 else sum(numbers) end

It's more like the ternary operator than a switch statement.

On Mon, 2003-05-19 at 02:59, James Taylor wrote:
> Hi everyone, I'm trying to figure out how to get CASE working in a sum
> aggregate function.  Pretty simple query:
>
> select sum(numbers) from lists where uid=1;
>
> It's possible that there may be 0 rows where uid == 1.  Instead of
> returning 1 blank row, I want it to return '0'.  So, I tried this:
>
> select case(sum(numbers)) when null then 0 else sum(numbers) end from
> list_results;

Use Coalesce:

SELECT coalesce(sum(numbers), 0) FROM lists WHERE uid = 1;

To use case, efficiently, if you really want:

SELECT CASE WHEN sum_numbers IS NULL THEN 0           ELSE sum_numbers      END AS sum_numbers FROM (SELECT
sum(numbers)AS sum_numbers         FROM lists        WHERE uid = 1      ) as tab; 


--
Rod Taylor <rbt@rbt.ca>

PGP Key: http://www.rbt.ca/rbtpub.asc

On Sun, 18 May 2003 23:59:46 -0700, "James Taylor"
<jtx@hatesville.com> wrote:
>select case(sum(numbers)) when null then 0 else sum(numbers) end from
>list_results;
>
>That... Doesn't work.

SELECT CASE WHEN SUM(numbers) IS NULL THEN 0 ELSE SUM(numbers) END ...

or

SELECT COALESCE(SUM(numbers), 0) FROM ...

ServusManfred

"James Taylor" <jtx@hatesville.com> writes:
> select case(sum(numbers)) when null then 0 else sum(numbers) end from
> list_results;

The reason the above doesn't work is that it expands toCASE WHEN sum(numbers) = null THEN ...
which always fails ("= null" does not mean "is null").

Easier would be SELECT COALESCE(sum(numbers), 0) FROM list_results
        regards, tom lane