Question

在我运行的网站上，我让用户评价各个帖子（3,2,1）。我使用以下SQL（在MySQL中）来获得每个值的投票百分比：

SELECT vote, COUNT(*) * t.factor AS pct
FROM ratings
JOIN (
    SELECT 100 / COUNT(*) AS factor
    FROM ratings
) AS t
GROUP BY vote
LIMIT 0, 30;

这适用于计算整个表的行百分比。现在，我需要仅针对特定帖子的百分比，在表格中通过“id”列标识。我怎么能这样做？

Answer 1

假设投票列保存投票的价值，即（3,2,1），那么您需要以下查询来列出每次投票的百分比：

SELECT r.id, r.vote, SUM(r.vote)/t.totalVotes AS percentOfVotes
FROM ratings r
JOIN (SELECT id, COUNT(id) AS totalVotes
      FROM ratings
      GROUP BY id ) AS t ON t.id = r.id
WHERE r.id = @id -- id of post you want
GROUP BY r.id, r.vote

Answer 2

这个问题似乎有点误导......但这就是我想象的那样。

SELECT vote, COUNT(*) * t.factor AS pct
FROM ratings
JOIN (
SELECT 100 / COUNT(*) AS factor
FROM ratings
where id = id of the post
) AS t
where id = id of the post
GROUP BY vote

Answer 3

有一种方法可行，但我被告知并不是世界上最有效的方法如下：

SELECT vote, COUNT(*) * t.factor AS pct
FROM ratings
JOIN (
    SELECT 100 / COUNT(*) AS factor
    FROM ratings
    WHERE id = 36
) AS t
WHERE id = 36
GROUP BY vote
LIMIT 0, 30;

我曾尝试在内部和外部选择中添加where子句，但不是两者都添加！当然有道理。

选择具有不同值的行的百分比

3 个答案: