Paging query template of Oracle

oracle Pagination query of ：
sql>select t2.* from 
(select t1.* ,rownum rn from 
(select * from emp) t1 where rownum<=6) t2 where rn>=4;
6--> Indicates the number of items taken
4--> It means to start from the clause
because oracle Internal optimization ！
For this statement ：
select emp.* ,rownum from emp where rownum>=4 and rownum<=6;
No results ！！！