https://leetcode-cn.com/problems/page-recommendations-ii/
1892.png
select a.user1_id user_id ,a.page_id page_id ,count(distinct a.user2_id)friends_likes from(
select distinct a.user1_id,a.user2_id,c.page_id
from
(select user1_id,user2_id from Friendship union select user2_id,user1_id from Friendship)a
left join Likes b on a.user1_id=b.user_id
left join Likes c on a.user2_id=c.user_id
where b.page_id!=c.page_id
)a left join (
select a.user1_id,a.user2_id,b.page_id
from (select user1_id,user2_id from Friendship union select user2_id,user1_id from Friendship) a,
(
select a.page_id,group_concat(user_id separator ',')user_list from(
select page_id from Likes
group by page_id
having count(distinct user_id)>1
)a left join Likes b on a.page_id=b.page_id
group by a.page_id
)b where find_in_set(a.user1_id,b.user_list)>0 and find_in_set(a.user2_id,b.user_list)>0
)b on a.user1_id=b.user1_id and a.user2_id=b.user2_id and a.page_id=b.page_id
where b.page_id is null
group by a.user1_id,a.page_id
# order by a.user1_id,a.page_id
