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
    o.destination_city,
    t.transport_name,
    ROUND(AVG(TIMESTAMPDIFF(DAY,o.order_date,o.delivery_date)),2) AS average_transport_duration,
    ROUND(SUM(c.total_cost),2) AS total_transport_cost
FROM
    transport_detail AS t
    INNER JOIN
    order_info AS o ON t.transport_id=o.transport_id
    INNER JOIN
    cost_data AS c ON o.order_id=c.order_id
GROUP BY
    o.destination_city,
    t.transport_name
ORDER BY
    o.destination_city,
    t.transport_name;