Top n percent top n%

Question

I do have the following code.

    SQL> select * from student_gpa;

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


        

Answer 1

You can try this:

WITH     got_analytics     AS
(
     SELECT     ssn, gpa
     ,     ROW_NUMBER () OVER (ORDER BY  gpa  DESC)     AS r_num
     ,     COUNT (*)     OVER ()                                AS n_rows 
     FROM  student_gpa   
)
SELECT       ssn, gpa
FROM       got_analytics 
WHERE       r_num     <= ROUND (n_rows * 12/*insert here your n%*/ / 100)
ORDER BY  gpa     DESC           

Answer 2

In Oracle, Top-N Queries like that are usually done using analytic functions, such as NTILE, so in your case:

WITH     got_tenth_gpa     AS
(
     SELECT     ssn, gpa
     ,     NTILE (10) OVER (ORDER BY gpa DESC)     AS tenth_gpa
     FROM     student_gpa
)
SELECT       ssn, gpa
FROM       got_tenth_gpa
WHERE       tenth_gpa     = 10
ORDER BY  gpa     DESC;

Answer 3

 create table student_gpa(ssn number,gpa number);

 insert into student_gpa values(1111,4);
 insert into student_gpa values(2222,4);
 insert into student_gpa values(3333,3);
 insert into student_gpa values(4444,2);

 select ssn,gpa from(
   select ssn, gpa,dense_rank() over (order by gpa desc) rn from student_gpa
     )
   where rn =1;

    ssn   gpa
   --------------
   1111   4
   2222   4

Answer 4

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));