SELECT T1.customerNumber, customerName, IFNULL(T1.productCode, 'N/A') productCode, IFNULL(T1.moneySpent, 'N/A') moneySpent
FROM
    (SELECT C.customerNumber, customerName, productCode, SUM(priceEach*quantityOrdered) as moneySpent
    FROM customers C
    LEFT JOIN orders O USING(customerNumber)
    LEFT JOIN orderdetails OD ON O.orderNumber = OD.orderNumber
    GROUP BY C.customerNumber, productCode) as T1
LEFT JOIN
    (SELECT customerNumber, MAX(moneySpent) as moneySpent
     FROM
        (SELECT C.customerNumber, customerName, productCode, SUM(priceEach*quantityOrdered) as moneySpent
        FROM customers C
        LEFT JOIN orders O USING(customerNumber)
        LEFT JOIN orderdetails OD ON O.orderNumber = OD.orderNumber
        GROUP BY C.customerNumber, productCode) tmp
     GROUP BY customerNumber
     ) AS T2
ON T1.customerNumber = T2.customerNumber and T1.moneySpent = T2.moneySpent
WHERE NOT (T1.moneySpent is not NULL and T2.moneySpent is NULL)
ORDER BY customerNumber