select *
? from (select t.app_id,
? ? ? ? ? ? ? ?t.emp_no,
? ? ? ? ? ? ? ?t.device_id,
? ? ? ? ? ? ? ?t.device_type,
? ? ? ? ? ? ? ?t.last_connect_time,
? ? ? ? ? ? ? ?t.device_model,
? ? ? ? ? ? ? ?rank() over(partition by t.device_type order by t.last_connect_time desc) rankNo
? ? ? ? ? from table_name t) e
?where e.rankNo = 1;

rank() over(partition by e.commandid order by e.systemid desc) rankNo （
partition by 根據什么進行分組，
order by 根據什么進行排序,
rank() over() 進行排名
rankNo 別名
）

select * from (select t1.*,row_number() over(partition by t1.deptno order by hiredate desc) as row_number from emp t1) where row_number=1