我可以编写自己的mySQL函数以在mySQL查询中使用吗？

DELIMITER //
CREATE FUNCTION square(n INT)
RETURNS INT
BEGIN
  RETURN n * n;
END //
DELIMITER ;

CREATE TABLE numbers (
  id INT AUTO_INCREMENT PRIMARY KEY,
  value INT
);

INSERT INTO numbers (value) VALUES (1), (2), (3), (4), (5);

SELECT id, value, square(value) AS squared_value FROM numbers;

+----+-------+---------------+
| id | value | squared_value |
+----+-------+---------------+
|  1 |     1 |             1 |
|  2 |     2 |             4 |
|  3 |     3 |             9 |
|  4 |     4 |            16 |
|  5 |     5 |            25 |
+----+-------+---------------+