题解 | #网易云音乐推荐(网易校招笔试真题)#

/*
select follower_id
from follow
where user_id = 1;

select music_id
from music_likes as ml
where user_id = 1;

select music_id
from music_likes as ml
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);
*/
select music_name
from music
where id in (
    select music_id
    from music_likes as ml
    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)
)
order by id;

我相信，这道题一定有其他看似简单的解答方法。但是，这道题我还是倾向于运用到经典的剥洋葱思路。

• 第一步：寻找user_id=1的关注者；
• 第二步：寻找user_id=1喜欢的music_id；
• 第三步：检索user_id=1的关注者喜欢的music_id，并排除第二步中的检索结果；
• 第四步：根据id检索music_name，并排序。