题解 | #返回每个订单号各有多少行数#
返回每个订单号各有多少行数
https://www.nowcoder.com/practice/cf1f8d4a514d455aa0468718fb411f41
本题概括下就是分组计数，采用group by + count()函数进行解答：
select order_num,count(order_num) order_lines from OrderItems group by order_num // 根据订单号进行分组 order by order_lines asc // 按订单个数升序排列