题解 | #返回每个顾客不同订单的总金额#

SELECT
    cust_id,(
        SELECT 
            SUM(order_total)
        FROM (
            SELECT order_num,SUM(item_price*quantity) AS order_total
            FROM OrderItems
            GROUP BY order_num 
        ) AS OT
        WHERE OT.order_num=O.order_num
    ) AS total_ordered
FROM
    Orders O
ORDER BY
    total_ordered DESC