如何使用mysql

Question

• 发布表2列： postid，问题

• answers表4列： ansid（PK），postid，userid，answer

• 投票表4列： postid，userid，ansid，upvote

单个帖子的总投票

SELECT sum(votes.upvote) as 'totalupvote' FROM `answers` 
            JOIN post on post.postid=answers.postid
            JOIN votes on votes.ansid=answers.ansid
            WHERE post.postid='1'

如何计算所有帖子的投票总数？

Answer 1

如果您希望每个postid总计：

SELECT postid, sum(upvote) as sumupvote 
FROM votes 
GROUP BY postid

如果您还想要question列：

select p.postid, p.question, v.sumupvote
from post p inner join (
  SELECT postid, sum(upvote) as sumupvote 
  FROM votes 
  GROUP BY postid
) v on v.postid = p.postid

Answer 2

显示所有帖子的投票总数

SELECT sum(votes.upvote) as 'totalupvote',post.postid,post.question FROM 
   votes inner JOIN post on post.postid=votes.postid            
        GROUP by post.postid