PL / SQL触发触发问题

CREATE OR REPLACE TRIGGER gradeInputCheck
BEFORE INSERT ON GRADE 
FOR EACH ROW
DECLARE
  newGrade GRADE.NUMERIC_GRADE%TYPE := :NEW.NUMERIC_GRADE;
    grade_too_low EXCEPTION;
    grade_too_high EXCEPTION;
BEGIN
  DBMS_OUTPUT.PUT_LINE(newGrade);
    IF (newGrade < 0) THEN
        RAISE grade_too_low;
    ELSIF (newGrade > 100) THEN
        RAISE grade_too_high;
    END IF;
EXCEPTION
    WHEN grade_too_low THEN
        DBMS_OUTPUT.PUT_LINE(\'Grades must be between 0 and 100\');
    WHEN grade_too_high THEN
        DBMS_OUTPUT.PUT_LINE(\'Grades must be between 0 and 100\');
END;

UPDATE grade SET numeric_grade = -1;