How to get top 3 record from aggregated column

Question

Hello,
i have a simple query which return all student in class with total marks. now i want to select top 3 student whose score is maximum. simple top three position. how can i use rank function here? or any other way to do that
select  st.sti_roll_no  ,st.sti_name , sum(rd.rd_obt_marks) as  mycol  from rd_result_detail rd , rm_result_master rm, sti_student_info st
where rm.rm_result_id = rd.rd_result_id
and st.sti_roll_no= rd.rd_student_id
--and  rd.rd_student_id = 'MBP10293'
and rm.rm_semester = 3
and rm_session = 2009
and rm_batch= 3
and rm.rm_exam_type ='FINAL TERM'
and rm.rm_class_id = 'MBA'
group by st.sti_name, st.sti_roll_no
order by st.sti_roll_no;

Answer 1

Not sure!!!!!!!!!!!!!
with t as
(select  st.sti_roll_no  ,st.sti_name , sum(rd.rd_obt_marks) as  mycol  from rd_result_detail rd , rm_result_master rm, sti_student_info st
where rm.rm_result_id = rd.rd_result_id
and st.sti_roll_no= rd.rd_student_id
--and  rd.rd_student_id = 'MBP10293'
and rm.rm_semester = 3
and rm_session = 2009
and rm_batch= 3
and rm.rm_exam_type ='FINAL TERM'
and rm.rm_class_id = 'MBA'
group by st.sti_name, st.sti_roll_no
order by st.sti_roll_no)
select sti_roll_no  ,sti_name,mycol,dense_rank()over(order by mycol desc) rnk
from t
--where rnk<=3
SQL> ed
Wrote file afiedt.buf
  1  select e.* from (select empno,ename,sal,dense_rank()over(order by sal desc) rnk
  2* from emp)e where rnk<=3
SQL> /
     EMPNO ENAME             SAL        RNK
      7839 KING             5000          1
      7788 SCOTT            3000          2
      7902 FORD             3000          2
      7566 JONES            2975          3