mysql - 给定一个用户，选择具有最常见评分的用户

Question

假设我有一个评级表:

create table ratings (
    user_id int unsigned not null,
    post_id int unsigned not null,
    rating set('like', 'dislike') not null,
    primary key (user_id, post_id)
);

对于id 1的给定用户，我如何选择具有更多共同喜欢的用户？不喜欢的用户有哪些共同点？具有更多评分(喜欢或不喜欢)的用户有什么共同点？我想这些查询会非常相似，但我还无法弄清楚其中的任何一个。我将更新我取得的任何进展。

感谢任何帮助，谢谢!

Answer 1

select
    r1.user_id as user1
    ,r2.user_id as user2
    ,r1.rating as rating
    ,count(*) as num_matching_ratings
from
    ratings r1 
    inner join ratings r2
        on r1.post_id = r2.post_id 
            and r1.rating = r2.rating
            and r1.user_id <> r2.user_id --don't want to count
                                         --matches with self
where
    r1.user_id = 1 -- change this to any user, or use a
                   -- variable to increase reusebility
    and r1.rating = 'like' -- set this to dislike to common dislikes
group by
    r1.user_id
    ,r2.user_id
    ,r1.rating
having
    count(*) > 1 --show only those with more than 1 in common
order by
    count(*) desc
/* limit 1 -- uncomment to show just the top match */

通过将表连接在一起，我们可以计算第二个用户对文章进行类似评分的次数。此查询将返回从最常见到最不常见的评估。如果取消注释“limit 1”语句，它将仅返回最常见的匹配项。