题解 | 查询出每个运输方式在不同城市的平均运输时长以及总运输费用

select
    destination_city,
    transport_name,
    round(avg(DATEDIFF(delivery_date, order_date)), 2) as average_transport_duration,
    round(sum(total_cost), 2) as total_transport_cost
from
    order_info
    join transport_detail using (transport_id)
    join cost_data using (order_id)
group by
    destination_city,
    transport_name
    order by destination_city