题解 | 推荐内容准确的用户平均评分

# select
#     round((sum(t2.score) / count(distinct t1.rec_user)),3) as avg_score
# from
#     recommend_tb t1
#     left join user_action_tb t2 on t1.rec_user = t2.user_id
# where
#     t1.rec_info_l = t2.hobby_l
SELECT 
    AVG(score) AS avg_score
FROM 
    (SELECT DISTINCT u.user_id, r.rec_info_l, u.score
     FROM user_action_tb u
     JOIN recommend_tb r ON u.hobby_l = r.rec_info_l
     WHERE u.user_id = r.rec_user) AS distinct_scores;

我认为还是有必要加一个DISTINCT u.user_id, r.rec_info_l, u.score，因为一个用户可能推荐准确多条记录，这时候随机选一条就可以了，所以要对user_id加一个DISTINCT来约束