题解 | #返回每个订单号各有多少行数#

题意分析：

每个订单号（order_num）各有多少行数（order_lines），并按 order_lines对结果进行升序排序

• 每个订单号：使用 group by 分组
• 各有多少行数：count() 函数进行统计

select
    order_num,
    count(order_num) as order_lines
from
    OrderItems
group by
    order_num
order by
    order_lines