CREATE FUNCTION ufn_get_salary_level(salary DECIMAL(19, 4))
  RETURNS VARCHAR(20)
  BEGIN
    DECLARE result VARCHAR(20);
    SET result := (SELECT
                      CASE
                        WHEN salary < 30000 THEN 'Low'
                        WHEN salary BETWEEN 30000 AND 50000 THEN 'Average'
                        WHEN salary > 50000 THEN 'High'
                      END);
    RETURN result;
  END;