题解 | 返回顾客名称和相关订单号以及每个订单的总价

思路分析：

三表连接，分别根据cust_id和order_num进行连接，在OrderItems表中计算quantity * item_price

代码解释：

SELECT
	cust_name,
    Orders.order_num AS order_num,
    quantity * item_price AS OrderTotal
FROM
    Customers
JOIN
    Orders
    ON Customers.cust_id = Orders.cust_id
JOIN
    OrderItems
    ON Orders.order_num = OrderItems.order_num
ORDER BY
    cust_name,
    order_num;

本题中每位顾客只有一个订单，计算每个订单的quantity * item_price即可，假如在OrderItems表中每个顾客有多个订单，则需要进行分组聚合，用SUM(quantity * item_price) + GROUP BY....，但就本题而言不需要，如上直接连接后求每个订单的总金额即可。