finding the the first row with
CUME_DIST() >= function_argument.

Examples
--------

CREATE TABLE book_rating (name CHAR(30), star_rating TINYINT);

INSERT INTO book_rating VALUES ('Lord of the Ladybirds', 5);
INSERT INTO book_rating VALUES ('Lord of the Ladybirds', 3);
INSERT INTO book_rating VALUES ('Lady of the Flies', 1);
INSERT INTO book_rating VALUES ('Lady of the Flies', 2);
INSERT INTO book_rating VALUES ('Lady of the Flies', 5);

SELECT name, PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY star_rating)
 OVER (PARTITION BY name) AS pc FROM book_rating;
+-----------------------+------+
| name                  | pc   |
+-----------------------+------+
| Lord of the Ladybirds |    3 |
| Lord of the Ladybirds |    3 |
| Lady of the Flies     |    2 |
| Lady of the Flies     |    2 |
| Lady of the Flies     |    2 |
+-----------------------+------+
5 rows in set (0.000 sec)

SELECT name, PERCENTILE_DISC(0) WITHIN GROUP (ORDER BY star_rating) 
 OVER (PARTITION BY name) AS pc FROM book_rating;
+-----------------------+------+
| name                  | pc   |
+-----------------------+------+
| Lord of the Ladybirds |    3 |
| Lord of the Ladybirds |    3 |
| Lady of the Flies     |    1 |
| Lady of the Flies     |    1 |
| Lady of the Flies     |    1 |
+-----------------------+------+
5 rows in set (0.000 sec)

SELECT name, PERCENTILE_DISC(1) WITHIN GROUP (ORDER BY star_rating) 
 OVER (PARTITION BY name) AS pc FROM book_rating;
+-----------------------+------+
| name                  | pc   |
+-----------------------+------+
| Lord of the Ladybirds |    5 |
| Lord of the Ladybirds |    5 |
| Lady of the Flies     |    5 |
| Lady of the Flies     |    5 |
| Lady of the Flies     |    5 |
+-----------------------+------+
5 rows in set (0.000 sec)

SELECT name, PERCENTILE_DISC(0.6) WITHIN GROUP (ORDER BY star_rating) 
 OVER (PARTITION BY name) AS pc FROM book_rating;
+-----------------------+------+
| name                  | pc   |
+-----------------------+------+
| Lord of the Ladybirds |    5 |
| Lord of the Ladybirds |    5 |
| Lady of the Flies     |    2 |
| Lady of the Flies     |    2 |
| Lady of the Flies     |    2 |
+-----------------------+------

URL: https://mariadb.com/kb/en/percentile_disc/https://mariadb.com/kb/en/percentile_disc/