Missing out on hits when using count

Question

I'm using the count-function to sum up som numbers, these numbers are connected to diffrent users.
As long as a user have at least one number to his name, there is no problem. But if he doesn't, I don't get any hit. I tried with nvl-function, but it doesn't work, I guess beacuse it isn't a null-value in return.
What I would want to get is zero for those users that doesn't have any numbers to sum up.
The code looks something like this...
select user_id, name, count(a.hits)
from user, score a
where ....
group by ....

Answer 1

You would need an outer join between the two tables, like in:
SQL> create table usr
  2  (name varchar2(10))
  3  /
Table created.
SQL> create table score
  2  (usr_name varchar2(10)
  3  ,x int)
  4  /
Table created.
SQL> insert into usr values ('aa');
1 row created.
SQL> insert into usr values ('bb');
1 row created.
SQL> insert into usr values ('cc');
1 row created.
SQL> insert into usr values ('dd');
1 row created.
SQL> insert into score values ('aa', 10);
1 row created.
SQL> insert into score values ('bb', 99);
1 row created.
SQL> insert into score values ('cc', 98);
1 row created.
SQL>
SQL> select name
  2       , count(s.x)
  3  from usr   u
  4     , score s
  5   where u.name = s.usr_name (+)
  6   group by name
  7  /
NAME       COUNT(S.X)
aa                  1
bb                  1
cc                  1
dd                  0
SQL> select name
  2       , Count(s.x)
  3    from usr u
  4    left outer
  5    join score s
  6      on (u.name = s.usr_name)
  7   group by name
  8  /
NAME       COUNT(S.X)
aa                  1
bb                  1
cc                  1
dd                  0