mysql if语句判断变量

IF condition THEN
    statement_list;
[ELSEIF condition THEN]
    statement_list;
[ELSE]
    statement_list;
END IF;

DELIMITER //

CREATE PROCEDURE AdjustSalaryLevel()
BEGIN
    DECLARE emp_id INT;
    DECLARE emp_salary DECIMAL(10, 2);
    DECLARE emp_level VARCHAR(20);

    DECLARE cur CURSOR FOR SELECT id, salary FROM employees;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET @done = TRUE;

    OPEN cur;

    read_loop: LOOP
        FETCH cur INTO emp_id, emp_salary;
        IF emp_salary < 3000 THEN
            SET emp_level = 'Low';
        ELSEIF emp_salary BETWEEN 3000 AND 6000 THEN
            SET emp_level = 'Medium';
        ELSE
            SET emp_level = 'High';
        END IF;

        UPDATE employees SET salary_level = emp_level WHERE id = emp_id;
    END LOOP;

    CLOSE cur;
END //

DELIMITER ;