左连接只返回一条记录

Question

I want to join two tables. One is 'users' and the other is 'reviews'. What i want to achieve is all the users with their average and total ratings from reviews table. I get the desired result when the review table has the ratings for all the users. But when the reviews table is empty, i get only one record from users table. Currently there are 3 users in users table but the query is showing only one record.

I want to get all the users even when there is no record of a user in reviews table. Here is the query i am using

SELECT u.id, u.name, u.photo, COUNT(r.rating) AS totalratings,
                                ( SELECT ROUND (AVG(r.rating),0)
                                FROM reviews r
                                WHERE r.fk_receiver_id = u.id) AS avg_rating 
                                FROM
                                users u LEFT JOIN reviews r
                                ON r.fk_receiver_id = u.id 
                                WHERE u.role=2
                                GROUP BY r.fk_receiver_id

Answer 1

You are grouping by the wrong column; when it's null (it will be because of the left join) the grouping won't behave as you want. Your query sould look like:

SELECT
  u.id,
  max(u.name) as name,
  max(u.photo) as photo,
  COUNT(r.rating) AS totalratings,
  ROUND(AVG(r.rating), 0) AS avg_rating
FROM users u
LEFT JOIN reviews r ON r.fk_receiver_id = u.id
WHERE u.role = 2
GROUP BY u.id

See running example at DB Fiddle .