select music_name from music where id in
(
select music_id from music_likes left join follow on music_likes.user_id = follow.follower_id where follow.user_id=1
) and id not in
(select music_id from music_likes where user_id=1) 
order by id

思路：

1.求出user_id为1的人喜欢的音乐id

select music_id from music_likes where user_id=1

2.求出user_id为1的人关注的人喜欢的音乐id，将music_likes和follow表join连接即可

select music_id from music_likes left join follow on music_likes.user_id = follow.follower_id 
where follow.user_id=1

3.从music中筛选出来已关注人喜欢的音乐，并剔除自己喜欢的音乐

select music_id from music_likes left join follow on music_likes.user_id = follow.follower_id 
where follow.user_id=1
order by id