What is wrong with the following trigger before an update?

I have to implement the following trigger in mysql before an update is made on the enrollment table

Enforce the constraint that all letter grades must be one ofA, B, C, D (no +/-) in this database). Also ensure that the grade point value matches: A=4.0, B=3.0, C=2.0, D=1.0

  CREATE TABLE enrollment (    student_id CHAR(4) not null,    student_name VARCHAR(100) not null,    course_id CHAR(7) not null,    enroll_date DATE not null,    letter_grade CHAR(2),    grade_points DECIMAL(2,1),    PRIMARY KEY (student_id, course_id)  );  

This is what I have so far:

create trigger letter_grade_checker before update on enrollment   for each row    begin      if ((new.letter_grade != 'A' and new.grade_points != 4.0)      or (new.letter_grade != 'B' and new.grade_points != 3.0)      or (new.letter_grade != 'C' and new.grade_points != 2.0)      or (new.letter_grade != 'D' and new.grade_points != 1.0))      then SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid grade or grade_points provided';      end if;  end;  

Although it's not working for the following update statement:

UPDATE enrollment SET letter_grade = 'B', grade_points = 3.0      WHERE student_id = '9999' and course_id = 'CSC-399';  

https://stackoverflow.com/questions/65947671/what-is-wrong-with-the-following-trigger-before-an-update January 29, 2021 at 09:41AM