题解 | 推荐内容准确的用户平均评分

# EXISTS 很好用，为什么没人用
SELECT
    AVG(score) AS avg_score
FROM
    user_action_tb ua
WHERE EXISTS
    (
        SELECT 1 FROM recommend_tb r WHERE r.rec_info_l = ua.hobby_l AND r.rec_user = ua.user_id
    )