Oracle Analytic function Ntile

There is a need to divide the performance of the course into four grades for students to play a, B, C, D.

drop table course purge;
CREATE TABLE Course
(
ID number,
Grade number
);
Insert into course values (1,50);
Insert into course values (2,55);
Insert into course values (3,60);
Insert into course values (4,65);
Insert into course values (5,70);
Insert into course values (6,75);
Insert into course values (7,80);
Insert into course values (8,85);
Insert into course values (9,90);
Insert into course values (10,95);
Commit

Sql> Select Id,grade,ntile (4) over (order BY grade desc) til from course;
ID GRADE TIL
---------- ---------- ----------
10 95 1
9 90 1
8 85 1
7 80 2
6 75 2
5 70 2
4 65 3
3 60 3
2 55 4
1 50 4
10 rows have been selected.

Oracle Analytic function Ntile