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