CREATE FUNCTION ufn_get_salary_level(salary DECIMAL(19,4))
RETURNS VARCHAR(50)
BEGIN
	DECLARE salary_level VARCHAR(50);

	SET salary_level := CASE
     WHEN salary < 30000 THEN 'Low'
     WHEN salary BETWEEN 30000 AND 50000 THEN 'Average'
     ELSE 'High'
     END;
RETURN salary_level;
END

CREATE PROCEDURE usp_get_employees_by_salary_level(salary_level VARCHAR(20))
BEGIN
START TRANSACTION;
	SELECT e.first_name, e.last_name
    FROM employees AS e
    WHERE ufn_get_salary_level(e.salary) LIKE salary_level
    ORDER BY e.first_name DESC, e.last_name DESC;

END