MYSQL ifelse語句

SET GLOBAL log_bin_trust_function_creators = 1;

DELIMITER $$
CREATE FUNCTION pro_salary_grade( salary INT) RETURNS CHAR
BEGIN
     DECLARE grade CHAR  DEFAULT "A";
    
    IF salary<5000  THEN SET grade ="E";
    ELSEIF salary<10000 THEN SET grade ="D";
    ELSEIF salary<15000 THEN SET grade ="C";
    ELSEIF salary<20000 THEN SET grade ="B";
    ELSE SET grade="A";
    END IF;
    
    RETURN grade;
    
END $$
DELIMITER ;

SELECT pro_salary_grade(16000);