select t1.exp_type, round(avg(timestampdiff(second,t2.out_time,t2.in_time)/3600),1) as time
from express_tb t1
left join exp_action_tb t2
on t1.exp_number = t2.exp_number
group by t1.exp_type
order by time asc

注意timestampdiff 使用hour做参数可能计算会报错