Top n percent top n%

Question

I do have the following code.

    SQL> select * from student_gpa;

    SSN                    GPA
    --------------- ----------
   22222                          


        

Answer 1

First 30 percent with 2 selects:

select ssn,gpa from(
select ssn, gpa,rank() over (order by gpa asc) as rn, count(*) over() as cnt
from student_gpa
)
where rn < 0.3*cnt ;

Solution with 4 selects and rownum (very ugly):

select ssn,gpa from(
select ssn, gpa
from student_gpa
)
where rownum < 0.3*(select count(*) from (select ssn, gpa from student_gpa));