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

#按照运输方式分组查询每个运输方式在不同城市的平均运输时长（交货日期 - 下单日期）以及总运输费用。
#查询出来的数据按照destination_city字段升序排列，如果destination_city一致，按照transport_name升序排列。
select destination_city,transport_name,
        round(avg(timestampdiff(day,order_date,delivery_date)),2) as average_transport_duration,
        sum(total_cost) as total_transport_cost
from transport_detail as a
inner join order_info as b
on a.transport_id = b.transport_id
inner join cost_data as c
on b.order_id = c.order_id
group by destination_city,transport_name
order by destination_city,transport_name