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(timestampdiff(day,order_date,delivery_date)),2) average_transport_duration,
    round(sum(total_cost),2) total_transport_cost
from
    transport_detail t1 join order_info t2 on t1.transport_id = t2.transport_id
    join cost_data t3 on t2.order_id = t3.order_id
group by
    destination_city, transport_name
order by
    destination_city, transport_name