oracle 分析函数

一个月百万条记录，create_date已分区，查询还是很慢，大于1分钟

 
select *
  from (select row_.*, rownum rownum_
          from (SELECT *
                  FROM jje_admin.T_NBP_MAIL_MESSAGE
                 where 1 = 1
                   AND create_date >= date '2015-02-01'
                 order by create_date desc) row_)
 where rownum_ >= 1
   and rownum_ <= 19

使用分析函数，速度在15秒左右

select *
  from (select a.*, rank() over(order by create_date desc) xh
          from jje_admin.T_NBP_MAIL_MESSAGE a
         where create_date >= date '2015-02-01')
where xh < 20;