select customer.cust_name,sale_item.book_no ,sum(qty) 总数量,sum(qty*unit_price)/sum(qty) 平均单价 from sales,customer,sale_item where sales.cust_name=customer.cust_name and sale_item.order_no=sales.order_no group by customer.cust_name,sale_item.book_no order by customer.cust_name,sale_item.book_no