select 
    destination_city,
    transport_name,
    round(avg(datediff(delivery_date,order_date)),2) as average_transport_duration,
    round(sum(total_cost),2) as total_transport_cost
from order_info o
join cost_data c using(order_id)
join transport_detail t using(transport_id)
group by 1,2
order by 1,2;