题解 | #网易云音乐推荐(网易校招笔试真题)#

select music_name from music where id in (select music_id from music_likes where user_id in (select follower_id from follow where user_id=1)and music_id not in (select music_id from music_likes where user_id=1) )

1.首先查询在follow 表中用户 music_id 时，他的关注人的follower_id，

select follower_id from follow where user_id=1

2.在music_likes表中用户user_id 是follower_id ，查询出music_id，并且限定music_id 不是user_id=1的music_id

#用户user_id 是follower_id

select music_id from music_likes where user_id in (select follower_id from follow where user_id=1)

#并且限定music_id 不是user_id=1的music_id

music_id not in (select music_id from music_likes where user_id=1) )

**推荐其关注的人喜欢的音乐。不要推荐该用户已经喜欢的音乐，

总的来说就是select music_id from music_likes where user_id in (select follower_id from follow where user_id=1) and music_id not in (select music_id from music_likes where user_id=1)

3.最后在表music中查询music_name

select music_name from music where id in (select music_id from music_likes where user_id in (select follower_id from follow where user_id=1)and music_id not in (select music_id from music_likes where user_id=1) )