Question

我将表格命名为帖子

|id|user_id|title|description|

喜欢这样的表

|id|user_id|post_id|

这是我的sql代码

select count(likes.id) as like_count, posts.* from `posts` left join 
`likes` on `likes`.`post_id` = `posts`.`id` where `posts`.`status` = 'A' 
group by `posts`.`id` order by `like_count` desc LIMIT 6

结果如下

|like_count |  id | user_id | title | description |
---------------------------------------------------
     17     | 723 |   12    | ...   | ....        |
     15     | 721 |   15    | ...   | ....        |
     14     | 711 |   12    | ...   | ....        |
     13     | 700 |   12    | ...   | ....        |
     12     | 800 |   11    | ...   | ....        |
     12     | 920 |   12    | ...   | ....        |

如您所见，user_id 12正在重复这一次，我只希望一个用户发布一条帖子。

有没有办法选择每个用户最喜欢的帖子，并让user_id不重复。

Answer 1

我知道这可能不是最有效的解决方案，但这是我想到的第一个。不幸的是，MySQL不支持窗口函数，因此任务比使用窗口函数的方法更难，更不优雅。

每个用户最喜欢的帖子会重复user_id，如果碰巧有多个帖子的数量相同且该数字对特定用户来说最大：

select
  user_likes.post_user_id,
  user_likes.like_count,
  p.id as post_id,
  p.title,
  p.description
from (
  select 
    p.user_id         as post_user_id, 
    MAX(l.like_count) as like_count
  from posts p
  inner join (select post_id, count(*) as like_count from likes group by post_id) l on p.id = l.post_id
  group by p.user_id
  ) user_likes
  inner join (select post_id, count(*) as like_count from likes group by post_id) l on user_likes.like_count = l.like_count
  inner join posts p on l.post_id = p.id

如果你真的需要每个用户一行，那么如果不同帖子的喜欢数量相关，你需要选择一个策略来只检索其中一个。例如，您可以通过在post_id上添加分组并获取其值min()并加入post表来检索其标题和说明，从而获取较旧的那个。

在这种情况下，上述脚本的修改如下所示：

select
  most_liked_post.post_user_id,
  most_liked_post.like_count,
  most_liked_post.post_id,
  p.title,
  p.description
from (
  select
    user_likes.post_user_id,
    user_likes.like_count,
    MIN(l.post_id) AS post_id
  from (
    select 
      p.user_id         as post_user_id, 
      MAX(l.like_count) as like_count
    from posts p
    inner join (select post_id, count(*) as like_count from likes group by post_id) l on p.id = l.post_id
    group by p.user_id
    ) user_likes
    inner join (select post_id, count(*) as like_count from likes group by post_id) l on user_likes.like_count = l.like_count
  group by user_likes.post_user_id, user_likes.like_count
  ) most_liked_post
  inner join posts p on most_liked_post.post_id = p.id

Mysql从分组表中选择唯一字段

1 个答案: