Let’s make the previous challenge more useful. In addition to returning the customer name and order number, add a third column named OrderTotal containing the total price of each order. There are two ways to do this, you can create the OrderTotal column using a subquery on the OrderItems table, or you can join the OrderItems table to the existing tables and use an aggregate function. Here’s a hint, watch out for where you need to use fully qualified column names.

-- Solution using subqueries
SELECT cust_name,
       (SELECT Sum(item_price*quantity)
       FROM OrderItems
       WHERE Orders.order_num=OrderItems.order_num) AS OrderTotal
FROM Customers, Orders
WHERE Customers.cust_id = Orders.cust_id
ORDER BY cust_name, order_num;

-- Solution using joins
SELECT cust_name,
       Sum(item_price*quantity) AS OrderTotal
FROM Customers, Orders, OrderItems
WHERE Customers.cust_id = Orders.cust_id
 AND Orders.order_num = OrderItems.order_num
GROUP BY cust_name, Orders.order_num
ORDER BY cust_name, order_num;

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