SQL 向用户推荐好友喜欢的音乐

问题描述：向用户 user_id = 1 推荐其关注的人喜欢的音乐

有如下三个表：

1. 用户关注表 follow
   
2. 用户喜欢的音乐 music_likes
   
3. 音乐名字表 music

create table follow
(
  user_id int,
  follower_id int
);

insert into follow values (1,2);
insert into follow values (1,4);
insert into follow values (1,5);

create table music_likes
(
  user_id int,
  music_id int
);

insert into music_likes values (1,20);
insert into music_likes values (1,30);
insert into music_likes values (1,40);
insert into music_likes values (2,10);
insert into music_likes values (2,20);
insert into music_likes values (2,30);
insert into music_likes values (4,10);
insert into music_likes values (4,20);
insert into music_likes values (4,30);
insert into music_likes values (4,60);

create table music
(
  id int,
  music_name char(10)
);

insert into music values (10,'a');
insert into music values (20,'b');
insert into music values (30,'c');
insert into music values (40,'d');
insert into music values (50,'e');
insert into music values (60,'f');

select music_name from  music where
    id in
    (
        select distinct music_id from music_likes where user_id in
        (
            select follower_id from follow where user_id = 1
        ) 
    ) 
    and id not  in
    (
        select music_id from music_likes where user_id = 1
    ) 
    order by id asc
;

推荐结果：