题解 | 统计快递运输时长

select exp_type,round(avg(duration),1) AS time
FROM(   
    SELECT a.exp_type,round(TIMESTAMPDIFF(MINUTE,b.out_time,b.in_time)/60,1) AS duration
    FROM express_tb AS a
    JOIN exp_action_tb AS b
    ON a.exp_number = b.exp_number
) AS c
GROUP BY exp_type
ORDER BY time ASC

此题ez，先通过表联选出每个商品的类型和运送时间(由于要保留一位小数所以我用的是时间相减取分钟数再除以60得到间隔小时数),然后就可以GROUP BY + avg聚合函数解决了