如何使用JOIN命令使用SQL查询获取所有记录（与Distinct相关）

Question

This is my SQL Query

SELECT tmdb_movies.movie_title
,GROUP_CONCAT(DISTINCT recommendations.recommendations_vote_average) as recommendations_vote_average

FROM tmdb_movies 

LEFT JOIN recommendations ON recommendations.recommendations_tmdb_id=tmdb_movies.tmdb_id

Where tmdb_movies.tmdb_id=155

GROUP BY tmdb_movies.movie_title

This is how my recommentions able looks like:

So, now ,GROUP_CONCAT(DISTINCT recommendations.recommendations_vote_average) as recommendations_vote_average If I use DISTINCT here, then it do not show vote_average of the following movies: The Matrix, Inception, Iron Man 2, Captain America: The First Avenger . +it shows wrong vote_average of all movies (leaving first)

If i do not use Distinct then it shows 7.5 in all records.

How to solve this problem? Let me know, if you need more information.

Answer 1

If you need the average recommendation, you can use the AVG aggregate function:

SELECT tmdb_movies.movie_title
,AVG( recommendations.recommendations_vote_average) as recommendations_vote_average
FROM tmdb_movies 
LEFT JOIN recommendations ON recommendations.recommendations_tmdb_id=tmdb_movies.tmdb_id
Where tmdb_movies.tmdb_id=155
GROUP BY tmdb_movies.movie_title

Answer 2

Try This:

        SELECT tmdb_movies.movie_title,
        GROUP_CONCAT(recommendations.recommendations_vote_average) 
         as recommendations_vote_average
        FROM tmdb_movies 
        LEFT JOIN (select * from recommendations group by recommendations_vote_average) 
        recommendations 
        ON recommendations.recommendations_tmdb_id=tmdb_movies.tmdb_id 
        Where tmdb_movies.tmdb_id=155
        GROUP BY tmdb_movies.movie_title