如果表非常大，需要用rownum查詢指定的幾條，下面命令可以實現(xiàn)

select * from(

select *

from T_NB_COPY t

order by create_time desc

) b where rownum <= 5

去重及時間段獲取

select distinct t.device_id from T_RECEIVE_LOG t where ?t.receive_time <= to_date('2018-02-28 00:00:00','yyyy-mm-dd hh24:mi:ss') and t.receive_time >= to_date('2018-02-27 00:00:00','yyyy-mm-dd hh24:mi:ss')