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 
oi.destination_city,
td.transport_name,
round(avg(timestampdiff(day,oi.order_date,oi.delivery_date)),2) as average_transport_duration,
round(sum(cd.total_cost),2) as total_transport_cost
from order_info oi
inner join cost_data cd
on cd.order_id = oi.order_id
inner join transport_detail td
on td.transport_id = oi.transport_id
group by oi.destination_city,
td.transport_name
order by 
destination_city asc , transport_name asc