1、查询user_id=1 的用户喜欢的音乐
select music_id from music_likes where user_id=12、查询user_id=1 的用户关注人的id
select follower_id from follow where user_id=13、将两张表连接,筛选用户id在2表范围内,音乐id不在1表范围内的信息
select distinct music_name from music_likes a join music b on a.music_id=b.id where a.user_id in (select follower_id from follow where user_id=1) and b.id not in (select music_id from music_likes where user_id=1) order by b.id;