Oracel 中的分页

--效率低

select * from (select rownum rn, d.* from table d )p where p.rn<=20 and p.rn>=10;

select * from (select rownum rn, d.* from table d  )p where p.rn between 10 and 20;

--效率高 

select * from (select rownum rn, d.* from table d where rownum<=20 )p where p.rn>=10;

　　

select * from (select rownum rn, d.* from table d where rownum<=20 )p where p.rn>=10;
为什么不直接用 

select  rownum rn, d.* from table d where rownum between 10 and 20

select * from (select rownum rn, t.* from ( select d.* from table d order by 1 desc )t where rownum<=20 )p where p.rn>=10;