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 ...