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,
sum(total_cost) total_transport_cost
from cost_data c join order_info o on c.order_id = o.order_id 
join transport_detail t on o.transport_id = t.transport_id
group by destination_city,transport_name
order by destination_city,transport_name