题解 | #返回每个顾客不同订单的总金额#

# SELECT cust_id, 
#         (SELECT SUM(quantity*item_price)
#         FROM OrderItems
#         WHERE OrderItems.order_num = Orders.order_num) as total_ordered
# FROM Orders
# Order by total_ordered DESC       

SELECT 
    o.cust_id cust_id,
    tb.total_ordered total_ordered
FROM (
    SELECT
        order_num,
        SUM(item_price * quantity) total_ordered
    FROM
        OrderItems
    GROUP BY
        order_num
    ) tb inner join
    Orders o
on
    tb.order_num = o.order_num
ORDER BY
    total_ordered DESC;