MySQL Stored Function with RETURN value

CREATE TABLE mytable(
  id      INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name    VARCHAR(20),
  salary  INT UNSIGNED NOT NULL
);

INSERT INTO mytable (name, salary) VALUES ('John Smith',5000), ('Tom Wright',900);
SELECT * FROM mytable;

DELIMITER $$

CREATE FUNCTION SalaryLevel(
    salary INT
)
RETURNS VARCHAR(5)
DETERMINISTIC
BEGIN
    DECLARE salaryLevel VARCHAR(5);

    CASE
      WHEN salary > 4000 THEN
        SET salaryLevel='HIGH';
      WHEN salary>1000 AND salary<= 4000 THEN
        SET salaryLevel='MIDLE';
      ELSE
        SET salaryLevel='LOW';
    END CASE;

    RETURN (salaryLevel);
END$$

DELIMITER ;

SELECT name, salary, SalaryLevel(salary) FROM mytable;
+------------+--------+---------------------+
| name       | salary | SalaryLevel(salary) |
+------------+--------+---------------------+
| John Smith |   5000 | HIGH                |
| Tom Wright |    900 | LOW                 |
+------------+--------+---------------------+
2 rows in set (0.00 sec)