PHP/MySQL的計算與相同的外鍵

Question

項目之間的區別我有一個表items的列id，name和一個表ratings與id，itemid，rating。我想要做的是返回結果，其中兩個評分相同的itemid之間的差異最大，按降序排列。

Answer 1

你可以通過減去最大額定值從最低等級，順序爲：

SELECT i.* 
FROM  items i 
JOIN  (SELECT itemid, MAX(rating) - MIN(rating) AS diff 
      FROM  ratings 
      GROUP BY itemid) r ON i.id = r.itemid 
ORDER BY diff DESC