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