如何从 join table table 派生数据

Question

我有 3 个 table 如下。现在从 Sell_Table 开始，我如何推导出 Country_Cod？我如何使用 Prod_Table 作为其他两个 table 之间的桥梁？

select count(Sell_Table.id), Country_Cod, avg(Sell_Table.Ammount)
from sell_table
left join ?
group by Country_Cod

谢谢

1)Country table
+--- -+-------------+
| id  | Country_Cod |
+---- +-------------+
| 101 | IT          |
| 102 | US          |
| 103 | GB          |
| 104 | TR          |
+-----+-------------+

2) Prod_Table
+-----+------------+---------+
| id  | Country_id | Sell__id|
+---- +------------+---------+
| 101 |101         | 101     |
| 102 |102         |         |
| 103 |102         | 102     |
| 104 |103         |         |
+-----+------------+---------+

3) Sell_Table
+-----+------------+----------+
| id  | Prod_id    | Amount   |
+---- +------------+----------+
| 101 |101         | 100      |
| 102 |103         | 200      |
| 103 |107         | 300      |
| 104 |110         | 400      |
+-----+------------+----------+

Answer 1

您似乎想要两个连接：

select s.id, c.country_code, s.amount
from sell s
inner join prod p on p.id = s.prod_id
inner join country c on c.id = p.country_id

如何从 join table table 派生数据

How to derive a data from join table table

mysql

sql

inner-join