oracle分页！

select * from
(select a.*,rownum rn from 
(select * from student order by sid) a where rownum <=30)
where rn>=20

1.根据ROWID来分
select * from t_xiaoxi where rowid in(select rid from (select rownum rn,rid from(select rowid rid,cid from 

t_xiaoxi  order by cid desc) where rownum<10000) where rn>9980) order by cid desc;
执行时间0.03秒
2.按分析函数来分
select * from (select t.*,row_number() over(order by cid desc) rk from t_xiaoxi t) where rk<10000 and rk>9980;
执行时间1.01秒
3.按ROWNUM来分
select * from(select t.*,rownum rn from(select * from t_xiaoxi order by cid desc) t where rownum<10000) where 

rn>9980;执行时间0.1秒
其中t_xiaoxi为表名称，cid为表的关键字段，取按CID降序排序后的第9981-9999条记录，t_xiaoxi表有70000多条记录
个人感觉1的效率最好，3次之，2最差