给关系人推荐歌曲
网易云音乐推荐(网易校招笔试真题)
https://www.nowcoder.com/practice/048ed413ac0e4cf4a774b906fc87e0e7
with t as( select f.user_id, m_n1.id id1, m_n1.music_name name1, follower_id, m_n2.id id2, m_n2.music_name name2 from follow f left join music_likes m1 on f.user_id=m1.user_id left join music m_n1 on m1.music_id=m_n1.id left join music_likes m2 on follower_id=m2.user_id left join music m_n2 on m2.music_id=m_n2.id ), t2 as( select distinct id2, name2 from t where user_id=1 and (name2 not in ( select name1 from t where user_id=1 ) or name1 is null) ) select name2 from t2 order by id2