从两个表中获取电影列表和评级MySQL LEFT JOIN

Question

I have a table

movies

movie_id
movie_name
language
cast 

ratings

id
movie_id
rating
comment

I need to fetch all movies details with average and total count of ratings.

If there is no rating for any movie, average rating and total ratings count must be zero.

for this i tried this MySQL query:

SELECT m.movie_id,movie_name,cast,language,AVG(rating) as average_rating,COUNT(rating) as total_rating 
FROM movies m 
LEFT JOIN ratings r ON m.movie_id=r.movie_id;

But this query not giving all movies lists from 'movies' table.

Please help. Thank you.

Answer 1

Use group by with movie_id so it will differentiate your result with unique movie_id.

SELECT m.movie_id,m.movie_name,m.cast,m.language,AVG(r.rating) as average_rating,COUNT(r.rating) as total_rating 
FROM movies m 
LEFT JOIN ratings r ON m.movie_id=r.movie_id
GROUP BY m.movie_id;

Answer 2

You need to add GROUP BY m.movie_id

SELECT
    `m`.`movie_id`, `m`.`movie_name`, `m`.`cast`, `m`.`language`,
    AVG(`r`.`rating`) `average_rating`, COUNT(`r`.`rating`) `total_rating`
FROM
    `movies` `m`
LEFT JOIN
    `ratings` `r`
ON
    `m`.`movie_id` = `r`.`movie_id`
GROUP BY
    `m`.`movie_id`;