COALESCE returns the leftmost non-null value. Perhaps what you wanted
was sum(coalesce(b,0)) instead of coalesce(0,sum(b))
>>> On Tue, Dec 12, 2006 at 9:22 AM, in message
<20061212152219.GC290@quartz.itdept.newn.cam.ac.uk>, Patrick Welche
<prlw1@newn.cam.ac.uk> wrote:
> Is this a bug, or don't I understand coalesce()?
>
> create table test (a int, b int);
> insert into test values (1,null);
> insert into test values (2,1);
> insert into test values (2,2);
> select * from test; -- returns:
> select sum(b) from test where a=1; -- null
> select sum(b) from test where a=2; -- 3
> select coalesce(0,sum(b)) from test where a=1; -- 0
> select coalesce(0,sum(b)) from test where a=2; -- 0
> delete from test where a=1;
> select coalesce(0,sum(b)) from test where a=2; -- 0 !
>
> So when I use coalesce() with sum(), I always get the constant. I
would
> have expected it only in the case where sum() returns null..
>
> What am I missing?