選擇具有不同值的行的百分比

Question

在我運行的網站上，我讓用戶爲各個帖子評分（3,2,1）。我用下面的SQL（在MySQL）來獲取每個值的得票百分比：

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; 

這工作正常計算行的百分比爲整個表。現在，我只需要一個特定帖子的百分比，在列表中由「id」列標識。我該怎麼做？

Answer 1

假設投票列包含了投票，即（3,2,1）的值，那麼你就需要下面的查詢每票製表的百分比：

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

這個問題似乎有點誤導......但這是我想象的樣子。這樣的作品，但我一直在勸

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

的一種方法是不是最有效的世界是這樣的：

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; 

我曾嘗試添加一個where子句內和外部選擇，但不是兩個！當然有意義。