MySQL选择2个关系的计数

Question

我正在实施一个使用MySQL和Node.js的投票系统，它目前运作良好，但有一个问题。我有一个表文章，其中包含两个关系 upvotes 和 downvotes 。

如果我抓取所有文章，我想计算 upvotes 和 downvotes 。第一个表正在使用

SELECT articles.*, count(downvotes.articles_id) 
as downvotes 
from articles 
left join downvotes 
on (articles.id = downvotes.articles_id) 
where articles.communities_id = '52' 
group by articles.id 
ORDER BY created_at 
DESC [![Sequel Pro][1]][1]

如何在查询中添加 upvotes ？

谢谢！

Matz的

Answer 1

你添加了downvotes的方式相同。此外，请确保您养成了格式化SQL的习惯，使其更易于阅读和调试。

SELECT 
    articles.*,
    COUNT(downvotes.articles_id) AS downvotes,
    COUNT(upvotes.articles_id) AS upvotes
FROM
    articles
        LEFT JOIN
    downvotes ON (articles.id = downvotes.articles_id)
        LEFT JOIN
    upvotes ON (articles.id = upvotes.articles_id)
WHERE
    articles.communities_id = '52'
GROUP BY articles.id
ORDER BY created_at DESC

Answer 2

为upvotes添加另一个左连接

SELECT articles.*, count(downvotes.articles_id) as downvotes 
from articles 
left join downvotes on (articles.id = downvotes.articles_id) 
left join upvotes on (articles.id = upvotes.articles_id) 
where articles.communities_id = '52' 
group by articles.id 
ORDER BY created_at DESC

Answer 3

好的，朋友发布了正确答案：

SELECT a.id, (SELECT COUNT(*) FROM downvotes d WHERE a.id=d.articles_id) AS `downs`, (SELECT COUNT(*) FROM upvotes u WHERE a.id=u.articles_id) AS `ups` FROM articles a ORDER BY a.id ASC

他告诉我问题是最后的小组。第一个左连接的结果将被第二个左连接覆盖。