Question

这是一个名为posts_votes

的表

id|discussion_id|post_id|user_id|vote_sign|
__________________________________________
1 |      1      |   1   |   1   |     1   |
2 |      1      |   1   |   2   |    -1   |
3 |      1      |   2   |   3   |     1   |
4 |      1      |   2   |   4   |     1   |
5 |      2      |   3   |   1   |    -1   |
6 |      2      |   4   |   2   |     1   |

我想用这些结果创建一个视图：

discussion_id|post_id|score
      1      |   2   | 2
      2      |   4   | 1

使用：

post_id是得分最高的帖子
得分为SUM（vote_sign）

我正在用群体折磨我的心灵并且有最大但我没有办法做到这一点.. =（

如果有人有想法......

谢谢;）

Answer 1

使用子查询首先计算得分并为每个discussion_id选择最高得分。然后join结果集以获得每个discussion_id的最高分数。

select t1.*
from (select discussion_id,post_id,sum(vote_sign) as score
      from posts_votes
      group by discussion_id,post_id) t1
join (select discussion_id,max(score) as maxscore 
      from (select discussion_id,post_id,sum(vote_sign) as score
            from posts_votes
            group by discussion_id,post_id) t
      group by discussion_id) t2 
on t1.discussion_id = t2.discussion_id and t1.score = t2.maxscore

Answer 2

select SUBSTRING_INDEX(GROUP_CONCAT(post_id ORDER BY sm DESC), ',', 1)  AS top_post, discussion_id, max(score) as score
from (
    select discussion_id, post_id, sum(vote_sign) as score
    from posts_votes
    group by post_id, discussion_id
) c
group by discussion_id

Answer 3

var b = new B();
b.virtualFunction();

Answer 4

此处查询对应于您的问题

select
  discussion_id, 
  max(post_id) as max_post_id,
  sum(vote_sign) as score
from
  posts_votes 
group by
  discussion_id;

MYSQL Multi group by和max

4 个答案: