join two tables along with count of records from second table based on condition

Question

I have following tables -

Here is SQLFIDDLE

categories

+-----------+-------------+
|  column   |    type     |
+-----------+-------------+
| id        | int(11)     |
| name      | varchar(40) |
| unit      | varchar(50) |
| is_active | tinyint(1)  |
+-----------+-------------+

and

products

+-------------+---------------+
|   column    |     type      |
+-------------+---------------+
| id          | int(11)       |
| category_id | int(11)       |
| name        | varchar(40)   |
| base_rate   | decimal(10,2) |
| is_active   | tinyint(1)    |
+-------------+---------------+

I want to get list of categories along with count of number of products active. If no products are active for a category it should return 0.

Somewhat like table below -

+----+--------+--------------+
| id |  name  | active_count |
+----+--------+--------------+
|  1 | Steel  |            1 |
|  2 | Cement |            2 |
+----+--------+--------------+

I have come up with following query -

SELECT c.id, c.name, c.unit, COUNT(p.category_id) as active_count 
FROM `categories` c 
JOIN `products` p
    ON c.id = p.category_id
WHERE ( p.is_active = 1 )
GROUP BY p.category_id;

This above query works only when there is at least one product active in each of category. If there are not products available it should return active_count as 0

How can I fix this ?

Here is SQLFIDDLE

Answer 1

Use LEFT JOIN instead of INNER JOIN:

SELECT c.id, c.name, c.unit, COUNT(p.category_id) as active_count 
FROM `categories` c 
LEFT JOIN `products` p
    ON c.id = p.category_id AND p.is_active = 1 
GROUP BY c.id;

It is also important to move predicate p.is_active = 1 from WHERE clause to ON, so that all records of categories table are returned by the query.