题解 | #返回产品名称和每一项产品的总订单数#

# 需要注意的是，count()函数自动忽略null值，当count的字段全为null值时，则计数为0
select prod_name, count(order_num) orders
from Products p
left join OrderItems o
on p.prod_id=o.prod_id
group by prod_name
order by prod_name;