SQL> ed
Wrote file afiedt.buf

  1  select ename, sal,rownum as ranking
  2  from (select ename, sal
  3  from emp order by sal desc)
  4* where rownum <= 5
SQL> /

ENAME             SAL    RANKING
---------- ---------- ----------
KING             5000          1
SCOTT            3000          2
FORD             3000          3
JONES            2975          4
BLAKE            2850          5

SQL> ed
Wrote file afiedt.buf

  1  select ename, sal, ranking
  2  from (select ename, sal, RANK() OVER (ORDER BY sal DESC NULLS LAST) as ranking
  3  from emp)
  4* where ranking <= 5
SQL> /

ENAME             SAL    RANKING
---------- ---------- ----------
KING             5000          1
SCOTT            3000          2
FORD             3000          2
JONES            2975          4
BLAKE            2850          5

SQL> ed
Wrote file afiedt.buf

  1*  SELECT * FROM EMP X WHERE &N=(SELECT COUNT(DISTINCT SAL) FROM EMP WHERE SAL>=X.SAL)
SQL> /
Enter value for n: 3
old   1:  SELECT * FROM EMP X WHERE &N=(SELECT COUNT(DISTINCT SAL) FROM EMP WHERE SAL>=X.SAL)
new   1:  SELECT * FROM EMP X WHERE 3=(SELECT COUNT(DISTINCT SAL) FROM EMP WHERE SAL>=X.SAL)

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20