select *
from tb t
where not exists(select 1
from tb
where device_id=t.device_id and port_id=t.port_id and occut_time>t.occut_time)
from tb t
where not exists(select 1
from tb
where device_id=t.device_id and port_id=t.port_id and occut_time>t.occut_time)
from tb t
where
occut_time=(select MAX(occut_time)
from tb
where device_id=t.device_id
and port_id=t.port_id)
select m.device_id, m.port_id,m.occur_time,m.status
from tab M
left join
(
select device_id, port_id, max(occur_time)
from tab
group by device_id, port_id) N
on m.device_id=n.device_id
and m.port_id=n.port_id
and m.occur_time=n.occur_time