题解 | #返回顾客名称和相关订单号以及每个订单的总价#

order_num 两个表都有，需要指明使用的是哪个表

SELECT cust_name, Orders.order_num, SUM(quantity * item_price) AS OrderTotal
FROM Customers 
INNER JOIN Orders on Customers.cust_id=Orders.cust_id
INNER JOIN OrderItems on OrderItems.order_num=Orders.order_num
GROUP BY cust_name, Orders.order_num
ORDER BY cust_name, Orders.order_num;

或者可用Using 声明

SELECT cust_name, order_num, SUM(quantity * item_price) AS OrderTotal
FROM Customers 
INNER JOIN Orders using(cust_id)
INNER JOIN OrderItems using(order_num)
GROUP BY cust_name, order_num
ORDER BY cust_name, order_num;