Oracle SQL join with counts returning null - sql

Question

I'm having a problem with the following query in Oracle SQL:
SELECT t.diif, t.mlf_response, v.total
FROM t_temp_rows t
LEFT OUTER JOIN
(SELECT a.diif, s.mlf_response, COUNT(a.customer_terid) total
FROM ter_details a
INNER JOIN lieu_details s ON a.lieu_id = s.lieu_id
WHERE a.customer_name = 'CUSTOMER_A' AND mlf_response IS NOT NULL
GROUP BY a.diif, s.mlf_response) v ON v.diif = t.diif AND v.mlf_response = t.mlf_response;
t_temp_rows contains all possible combinations for diif and mlf_response, regardless of whether they actually return counts in the subquery or not. I am hoping to get a count for every row in t_temp_rows, including 0 for rows with no count (I will add the NVL once it actually works).
If I run the query, rather than returning the counts in 'total' where there is a value and null elsewhere, I get null for every row.
Expected:
diif mlf_response total
---- ------------ -----
ABCD YES 12
ABCD NO 32
ABCE YES 54
ABCE NO 01
ABCF YES null
ABCF NO null
Actual:
diif mlf_response total
---- ------------ -----
ABCD YES null
ABCD NO null
ABCE YES null
ABCE NO null
ABCF YES null
ABCF NO null
What have I done wrong?

Answer 1

You need to add a.customer_name = 'CUSTOMER_A' to the left outer join because by adding it to the where, you are making it an inner join.
SELECT t.diif, t.mlf_response, v.total
FROM t_temp_rows t
LEFT OUTER JOIN
(SELECT a.diif, s.mlf_response, COUNT(a.customer_terid) total
FROM ter_details a ON a.customer_name = 'CUSTOMER_A'
LEFT OUTER JOIN lieu_details s ON a.lieu_id = s.lieu_id
WHERE mlf_response IS NOT NULL
GROUP BY a.diif, s.mlf_response) v ON v.diif = t.diif AND v.mlf_response = t.mlf_response;