题解 | #返回产品名称和每一项产品的总订单数#
返回产品名称和每一项产品的总订单数
https://www.nowcoder.com/practice/1c64fd9048364a58a8ffa541720359a4
select prod_name, count(order_num) orders
from Products a left join OrderItems b
on a.prod_id = b.prod_id
group by prod_name
order by prod_name;
-- 下面的不行，会显示none
select prod_name, orders
from Products a left join (
select count(order_num) orders,prod_id
from OrderItems
group by prod_id
) b on a.prod_id = b.prod_id
order by prod_name;
select count(order_num) orders
from OrderItems
group by prod_id;
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