Return Count Value back as 0 if emtpy or none - oracle

Question

I am running the following query in our database and I am trying to get the count value back as 0 if none are present, but having problems doing so. Could someone help assist and explain how to accomplish this
select state, count(phone_number) from VOIP_PHONE_NUMBER_POOL
where status = 3
group by state
order by state asc;
For example, currently my query is returning something back like this
State Count
AZ 25
When I want it to return the empty values and look like this
State Count
AZ 25
CA 0

Answer 1

This mimics what you have now:
SQL> with voip_phone_number_pool (state, phone_number, status) as
2 (select 'AZ', 1234, 3 from dual union all
3 select 'AZ', 2232, 3 from dual union all
4 select 'AZ', 4444, 3 from dual union all
5 select 'AZ', 7756, 1 from dual union all
6 --
7 select 'CA', 9999, 1 from dual
8 )
9 select state,
10 count(phone_number)
11 from voip_phone_number_pool
12 where status = 3
13 group by state
14 order by state;
ST COUNT(PHONE_NUMBER)
-- -------------------
AZ 3
SQL>
There's no row for the CA state which has status = 3, so it isn't returned by that query.
What you could do, is to use outer self-join in such a manner:
SQL> with voip_phone_number_pool (state, phone_number, status) as
2 (select 'AZ', 1234, 3 from dual union all
3 select 'AZ', 2232, 3 from dual union all
4 select 'AZ', 4444, 3 from dual union all
5 select 'AZ', 7756, 1 from dual union all
6 --
7 select 'CA', 9999, 1 from dual
8 ),
9 states as
10 (select distinct state from voip_phone_number_pool)
11 select s.state,
12 count(v.phone_number)
13 from states s left join voip_phone_number_pool v on v.state = s.state
14 and v.status = 3
15 group by s.state
16 order by s.state;
ST COUNT(V.PHONE_NUMBER)
-- ---------------------
AZ 3
CA 0
SQL>
the states CTE selects all states
it is then used in outer join with voip_phone_number_pool
note that condition (status = 3) has to be moved into join (line #14); if you leave it in the where clause, you won't get desired result

Answer 2

If there are no rows in the fact table (VOIP_PHONE_NUMBER_POOL) with a particular state, you will not get such a result from only querying that table.
You will need to join your fact table to a dimension table (a table with all possible states) in order to get the desired counts.
For example, assuming you have such a dimension table and it is named "state_info":
SELECT s.state,
COUNT(v.phone_number) AS phone_number_count
FROM state_info s
LEFT OUTER JOIN voip_phone_number_pool v
ON s.state = v.state
GROUP BY s.state;

Answer 3

SELECT s.state,
COUNT(v.phone_number) AS phone_number_count
FROM CORP_ACCT s
LEFT OUTER JOIN voip_phone_number_pool v
ON s.state = v.state
GROUP BY s.state;
worked for me