Re: [SQL] Problems using count() with a join

Doug Younger <postgres(at)mindspring(dot)com> writes:
> What I want is to get a count of # of users in each group, even if there
> are no users in the group.

> I have tried the following:
> SELECT t1.g_name,count(t2.g_id)
> FROM groups t1,users t2
> WHERE t1.g_id = t2.g_id
> GROUP BY t1.g_name;

> But it only give the counts of users in each group if there actually are
> users in that group.
> I want the count to be 0 if there are no users in the group.

Try SELECT as above plus

... UNION
SELECT t1.g_name, 0
FROM groups t1
WHERE NOT EXISTS(SELECT * FROM users t2 WHERE t1.g_id = t2.g_id);

Grotty, I know, but we don't have outer joins yet...

regards, tom lane