题解 | #统计每种性别的人数#

select a.cust_name,c.order_num,c.OrderTotal
from Customers a left join Orders b on a.cust_id=b.cust_id
          left join (select order_num,sum(quantity * item_price) as OrderTotal
                    from OrderItems
                    group by order_num) c on b.order_num = c.order_num
order by a.cust_name,c.order_num