SELECT order_num
FROM (
    SELECT order_num, SUM(quantity)
    FROM OrderItems
    GROUP BY order_num
    HAVING SUM(quantity) >= 100
) a
ORDER BY order_num

题解：

1.任务：查询订单号

2.限制：订单数量总和不低于100

3.排序

思路：

1.先写查询语句，查询订单号

2.要计算每个订单号的订单数量之和，使用sum函数和group by语句，

3.排序order by