MySQL 连接表、查找平均评分和排名答案

【问题标题】：MySQL Joining Table, Find Average Rating, and RankMySQL 连接表、查找平均评分和排名
【发布时间】：2020-11-29 02:29:00
【问题描述】：

如何计算平均评分，然后按最高平均评分和票数排序？

以下是我目前所拥有的......

members表

ID | name
---+------
 1 | Andrew
 2 | Anthony
 3 | John
 4 | Jane

member_ratings表

ID | id_gave_rating | id_rated | rating
---+----------------+----------+---------
 1 |        1       |     2    |    1
 2 |        2       |     3    |    4
 3 |        3       |     4    |    3
 4 |        4       |     2    |    5

当前查询

    $sql = "
    SELECT *, 
    m.id AS id, 
    c1.id AS id_rated, 
    c1.name AS name_rated
    FROM member_ratings AS m
    JOIN members AS c1 ON m.id_rated  = c1.id";

目标结果

id_rated | avg_rating | votes
---------+------------+--------
    3    |      4     |    1
    2    |      3     |    2
    4    |      3     |    1

【问题讨论】：

标签： mysql join count average

【解决方案1】：

您必须在member_ratings 中group by id_rated 并聚合：

select id_rated, 
       avg(rating) avg_rating,
       count(*) votes
from member_ratings
group by id_rated
order by avg_rating desc, votes desc

如果您还想了解会员的详细信息，您可以加入members：

select m.id, m.name, r.avg_rating, r.votes
from members m 
inner join (
  select id_rated, 
         avg(rating) avg_rating,
         count(*) votes
  from member_ratings
  group by id_rated
) r on r.id_rated = m.id
order by r.avg_rating desc, r.votes desc

或者：

select m.id, m.name, 
       avg(r.rating) avg_rating,
       count(*) votes
from members m inner join member_ratings r
on r.id_rated = m.id
group by m.id, m.name
order by avg_rating desc, votes desc

请参阅demo。

【讨论】：