mysql 加入 3 table 但 "COUNT" 是重复的

Question

我有 3 个这样的 table

订单table:

| id | product_id | status | created_at |
|----| ---------- | ------ | ---------- |
| 1  |     1      |  done  | 1607431726 |
| 2  |     7      |  done  | 1607431726 |
| 3  |     8      |  done  | 1607431726 |

产品table：

| id | user_id |    title    |  description  | created_at |
|----| ------- | ----------- | ------------- | ---------- |
| 1  |    1    |  product 1  | description 1 | 1607431726 |
| 7  |    3    |  product 2  | description 1 | 1607431726 |
| 8  |    3    |  product 3  | description 1 | 1607431726 |

评分table：

| id | client_id | content_type | content_id | rating | created_at |
|----| --------- | ------------ | ---------- | ------ | ---------- |
| 1  |     5     |     user     |      1     |    5   | 1607431726 |
| 2  |     4     |     user     |      3     |    5   | 1607431726 |
| 3  |     5     |     user     |      3     |    4   | 1607431726 |

从上面的 3 tables 中，我想得到 1 个结果，其中有一个字段 average_rating/user，总计 order/user，我想按 average_rating 排序] & total_rating 描述。大致是这样的结果：

| user_id | average_rating | total_order |
| ------- | -------------- | ----------- |
|    1    |      5.0       |     1       |
|    3    |      4.5       |     2       |

这是我的查询：

SELECT b.user_id, round(avg(c.rating), 1) as total_rating, COUNT(a.id) as total_order
    FROM orders a
        LEFT JOIN products b ON a.product_id=b.id
        LEFT JOIN ratings c ON c.content_id=b.user_id 
    WHERE a.status = 'done' 
        AND c.content_type = 'user'
    GROUP BY b.user_id, c.content_id;

但是对于我的查询，user_id 1 的总订单 return 1 和 user_id 3 的总订单 4，结果是：

| user_id | average_rating | total_order |
| ------- | -------------- | ----------- |
|    1    |      5.0       |     1       |
|    3    |      4.5       |     4       |

我已经尝试过 INNER JOIN、LEFT OUTER、RIGHT OUTER、RIGHT JOIN，但结果是一样的。谁能帮帮我？

Answer 1

每个产品有多个评级。一种选择使用 distinct:

SELECT p.user_id, 
    round(avg(r.rating), 1) as total_rating, 
    COUNT(distinct o.id) as total_order
FROM orders o
INNER JOIN products p ON o.product_id=p.id
INNER JOIN ratings r ON r.content_id=p.user_id 
WHERE o.status = 'done' AND r.content_type = 'user'
GROUP BY p.user_id, r.content_id;

mysql 加入 3 table 但 "COUNT" 是重复的

mysql join 3 table but the "COUNT" be duplicate

mysql

sql

count

aggregate-functions

left-join