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