快手一面SQL之相互关注数
来源VIP学员反馈的快手面试题【2024/05/15】
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SQL题目
- 有一张用户关注表dwd_online_user_follow_dd, 包含用户id（user_id）和关注者id（follower_id）
- 求相互关注的用户对
答案解析
模拟数据
insert into dwd_online_user_follow_dd values
('a', 'b'),('a', 'c'),('a', 'd'),('b', 'a'),('c', 'a'),('c', 'd');
解法1
select
t1.user_id,
t1.follower_id
from dwd_online_user_follow_dd t1
left join dwd_online_user_follow_dd t2
on t1.user_id = t2.follower_id and t1.follower_id = t2.user_id
where t2.user_id is not null;
解法2
select user_f
from (
select concat(follower_id,'-',user_id) as user_f
from dwd_online_user_follow_dd
union all
select concat(user_id,'-',follower_id) as user_f
from dwd_online_user_follow_dd
) t
group by user_f having count(*)>1;
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