Question

表如下：

1) Categories: id, name
2) Countries: id, name
3) Producers: id, name, country_id
4) Products: id, name, price, category_id, producer_id
5) Customers: id, name, surname, age, country_id
6) Customer_orders: id, customer_id, product_id, quantity, discount, order_date

我想找到每个国家/地区最受欢迎的商品类别（最受欢迎的商品类别-产品是由指定国家/地区的生产商生产的）

我当前的方法

select countries.name, categories.name, sum(cs.quantity) from countries
join producers on producers.country_id = countries.id
join products on products.producer_id = producers.id
join categories on categories.id = products.category_id
join customerorders as cs on cs.product_id = products.id
group by countries.name

这实际上不是一个好的解决方案。不确定如何执行此操作，我想应该按国家/地区对所有产品进行分组，然后针对每个国家/地区对每种产品类别（指定国家/地区的生产商生产的产品）的产品数量进行计数，最后找到购买最多产品的类别。

Answer 1

您需要修复group by，然后使用窗口功能：

select c.*
from (select co.name as country_name, c.name as category_name, sum(co.quantity) as total_qty,
             row_number() over (partition by co.name order by sum(co.quantity) desc) as seqnum
      from countries co join
           producers pr
           on pr.country_id = co.id join
           products p
           on p.producer_id = pr.id join
           categories c
           on c.id = p.category_id join
           customerorders co
           on co.product_id = p.id
      group by co.name, c.name
     ) c
where seqnum = 1;

这应该在MySQL 8+中有效。可以在早期版本中表达这一点，但是有点痛苦。

为每个国家/地区找到最受欢迎的产品类别-子查询

1 个答案: