Re: coalesce and aggregate functions

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?