COUNT rows in 3 tables including zero values with MySQL - mysql

Question

I have a MySQL 5.6 database with 3 tables:
job_offer
+----+----------+-------------+-----------+
| id | name | position_id | status_id |
+----+----------+-------------+-----------+
| 1 | John | 1 | 4 |
| 2 | Smith | 1 | 4 |
| 3 | Williams | 2 | 2 |
+----+----------+-------------+-----------+
position
+----+----------+
| id | name |
+----+----------+
| 1 | frontend |
| 2 | backend |
+----+----------+
status
+----+-----------+
| id | name |
+----+-----------+
| 1 | contacted |
| 2 | declined |
| 3 | rejected |
| 4 | interview |
+----+-----------+
I would like to build a query that can count all job offers by their position and statuses.
I have this query that performs almost the way I want it:
SELECT
position.name AS position_name,
status.name AS status_name
COUNT(job_offer.id) AS offers
FROM
job_offer
LEFT OUTER JOIN
position
ON job_offer.position_id = position.id
LEFT OUTER JOIN
status
ON job_offer.status_id = status.id
GROUP BY
position_name, status_name
Which gives me this result:
+---------------+-------------+--------+
| position_name | status_name | offers |
+---------------+-------------+--------+
| frontend | interview | 2 |
| backend | declined | 1 |
+---------------+-------------+--------+
The only problem is that I also need to display all existing statuses related to positions regardless of being NULL. So ideally it should look like this:
+---------------+-------------+--------+
| position_name | status_name | offers |
+---------------+-------------+--------+
| frontend | contacted | 0 |
| frontend | declined | 0 |
| frontend | rejected | 0 |
| frontend | interview | 2 |
| backend | contacted | 0 |
| backend | declined | 1 |
| backend | rejected | 0 |
| backend | interview | 0 |
+---------------+-------------+--------+
Is it possible to achieve this with one query? Thanks in advance for any help.

Answer 1

We can use a cross join approach between the position and status table to generate all possible combinations. Then, left join to job_offer and aggregate by position and status to find the counts:
SELECT
p.name AS position_name,
s.name AS status_name,
COUNT(jo.id) AS offers
FROM position p
CROSS JOIN status s
LEFT JOIN job_offer jo
ON jo.position_id = p.id AND
jo.status_id = s.id
GROUP BY
p.name,
s.name
ORDER BY
p.name,
s.name;
Demo