getting a query column to return 0 if nothing matches

I have a query like this (this one is simplified to illustrate my question):

select
l.email, p.practice_name, count(lp.provider_key) as patient_count
from
login l, provider p, login_provider lp
where
p.login_key = l.id
and
lp.provider_key = p.provider_key
group by
l.email, p.practice_name

It works fine but only returns rows where the provider key appears in the
login_provider table.
I want to show all rows where the first part of the WHERE clause is true,
regardless of whether the provider_key is in the login_provider table (in
that cause, I want to show 0 in that column).

In other words, currently if I run the above query, it will return 19 rows,
and if I run this one:
select
l.email, p.practice_name
from
login l, provider p
where
p.login_key = l.id

I get 57 rows. What I want is for the first query to also return 57 rows
and just show 0 for patient_count if the second part of the where clause
cannot be satisfied.

I'm sure this is a simple thing, but I'm not sure how do do it. Can anyone
help?
Thanks