Question

假设一个名为'users'的表，一个名为'posts'的表和一个名为'ratings'的表，其中包含每个用户对每个帖子的评级（“喜欢”或“不喜欢”）。

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)
);

鉴于帖子X，我想选择所有帖子Y，以便没有用户对他们进行评分，两者都喜欢。此外，如果可能的话，我想按照对其进行评分的普通用户的数量来订购这些帖子，这意味着与X最常见的“评分者”的帖子Y应首先出现。

我复制了迄今为止我所做的事情，但我认为这一切都不值得。感谢任何帮助，谢谢！

Answer 1

试试this fiddle。我不是100％确定我得到了你想要的东西，但是......如果它适合的话，请检查你自己的数据。

您还可以删除WHERE并将X.post_id AS this_post_id添加到FROM以获取所有帖子。

Answer 2

鉴于帖子X，我想选择所有帖子Y，以便没有评价他们的用户，都喜欢他们。

好的，所以给定以下数据集，当ID = 1时你会期望5和6（我知道你也不想显示ID = 1）：

+---------+---------+---------+
| POST_ID | USER_ID | RATING  |
+---------+---------+---------+
|       1 |       1 | like    | // ID = 1, so remove this post
|       1 |       2 | like    |
|       1 |       3 | like    |
|       1 |       4 | dislike |
|       2 |       1 | like    | // Double like, so remove this post
|       2 |       2 | dislike |
|       2 |       3 | like    |
|       2 |       4 | dislike |
|       3 |       1 | like    | // Double like, so remove this post
|       4 |       1 | dislike |
|       4 |       2 | like    | // Double like, so remove this post
|       5 |       1 | dislike |
|       5 |       2 | dislike |
|       5 |       5 | dislike |
|       6 |       1 | dislike |
+---------+---------+---------+

此查询将为您提供：

select distinct post_id from ratings r3
where r3.post_id not in (
  select r2.post_id from ratings r1
  join ratings r2
  on r1.post_id <> r2.post_id and r1.user_id = r2.user_id
  where (r1.post_id = 1 or r2.post_id = 1) and r1.rating = 'like' and r2.rating = 'like'
)

如果您还希望它们按照常见的评估者排序，则运行此查询：

select post_id from ratings r3
where r3.post_id not in (
  select r2.post_id from ratings r1
  join ratings r2
  on r1.post_id <> r2.post_id and r1.user_id = r2.user_id
  where (r1.post_id = 1 or r2.post_id = 1) and r1.rating = 'like' and r2.rating = 'like'
) and r3.user_id in (
  select user_id from ratings
  where post_id = 1
)
group by post_id
order by count(*) desc

这是example

给定一个帖子X，选择所有帖子Y，使得没有评价他们的用户都喜欢他们

2 个答案: