执行“加权”SQL查询

Question

在我目前的设置中，我有两个表：product和rating。

产品表

• PRODUCT_ID
• 评级

的product表包含了一大堆额外的信息，但对于这个问题，我专注于只有这两个领域。

评分表

• PRODUCT_ID
• 评级
• USER_ID（谁评估）
• is_admin - 对额定用户是否是管理员

原因布尔我们首先收集管理员评分，这是因为我们想要权衡管理员与普通用户（40％）相比，评分略高（60％）。 product表中的rating列等于所有管理员评分的AVG。在一般的评级是1和5

因此，对于每一个产品，我们必须考虑四个场景之间：

RATINGS BY  TOTAL 
USER ADMIN RATING 
---- ----- 
no no = 0 
yes no = AVG of user ratings (`ratings` table) 
yes yes = 0.6 AVG of admin ratings (`product_table`) + 0.4 AVG of user ratings (`ratings` table) 
no yes = AVG of admin ratings (`product_table`) 

目前检索数据集的SQL查询看起来是这样的：

$sql = "SELECT p.product_id, 
(COALESCE(p.rating,0)+COALESCE(j.sum,0))/(COALESCE(p.rating/p.rating,0) 
    + COALESCE(j.tot,0)) AS rating 
FROM product p 
LEFT JOIN 
    (SELECT SUM(rating) AS sum , 
     COUNT(rating) AS tot, 
     product_id FROM rating 
    WHERE is_admin_rating=FALSE GROUP BY product_id) j 
ON (p.product_id = j.product_id) LEFT JOIN product_description pd 
    ON (p.product_id = pd.product_id) LEFT JOIN product_to_store p2s 
    ON (p.product_id = p2s.product_id)"; 

然后，该查询会附加各种不同的排序选项（评级为默认值），此外，我们还使用LIMIT“分页”搜索结果。

有没有办法将加权评分纳入查询？或者我将不得不把它分解成几个查询？

Answer 1

因为这显然看起来像一个基于Web的系统，我会强烈建议有轻微的非正规化和5列的产品表套结对

UserRatings, UserCount, AdminRatings, AdminCount, FinalRating 

当任何条目添加或更新评级表，你可以应用一个简单更新触发器，像

update Product p, 
     (select r.product_id, 
       sum(is_admin_rating=FALSE, 1, 0) as UserCount, 
       sum(is_admin_rating=FALSE, rating, 0) as UserRatings, 
       sum(is_admin_rating=TRUE, 1, 0) as AdminCount, 
       sum(is_admin_rating=TRUE, rating, 0) as AdminRatings 
      from Ratings r 
      where r.product_id = ProductIDThatCausedThisTrigger 
      group by r.product_id) as PreSum 
    set p.UserCount = PreSum.UserCount, 
     p.UserRatings = PreSum.UserRatings, 
     p.AdminrCount = PreSum.AdminCount, 
     p.AdminRatings = PreSum.AdminRatings, 
     p.FinalRating = case when PreSum.UserCount = 0 and PreSum.AdminCount = 0 
           then 0 
          when PreSum.UserCount = 0 
           then PreSum.AdminRatings/PreSum.AdminCount 
          when PreSum.AdminCount = 0 
           then PreSum.UserRatings/PreSum.UserCount 
          else 
           (PreSum.UserRatings/PreSum.UserCount * .4) 
          /(PreSum.AdminRatings/PreSum.AdminCount * .6) 
          end 
    where p.product_id = PreSum.product_id 

这样一来，你就永远没有做单独的连接，以收视率表，并做汇总，将只得到更多数据的积累速度较慢。然后你的查询可以使用表格，而不必担心结合，每个人的计数和他们的评级将在那里。

壳体/当针对FinalRatings基本上是做它都包起来作为用户计数和管理计数的组合可以是0/0，+/0,0/+或+/+

So, if no count for either, the case/when sets rating to 0 
if only the user count has a value, just get that average rating (userRatings/userCounts) 
if only the admin count has a value, get admin avg rating (adminRatings/adminCounts) 
if BOTH have counts, you are taking the respective averages * .4 and * .6 respectively. This would be the one factoring adjustment you might want to tweak. 

尽管查询本身看起来有些怪异和令人困惑，但如果您查看“PreSum”查询，则仅针对刚刚进行评分的1种产品以及触发基础进行查询。然后，根据单个产品ID加入的结果进行简单更新。

使用此功能可能会为您提供更好的长期解决方案。