SELECT order_num, COUNT(order_num) AS items FROM OrderItems GROUP BY order_num HAVING items >= 3 ORDER BY items

这道题需要获取到order_num（订单号）的次数，找到次数大于3的，需要对order_num进行计数，然后对订单号进行分组，然后获取到次数大于3的订单数，再对次数进行排序