Simple trigger to update two columns in one table
Hope i have understand what you are saying correctly, following would be the code you may be looking for.

DELIMITER //
CREATE TRIGGER trig_1 before insert
ON  &lt;table_name&gt; FOR EACH ROW
BEGIN

   IF   new.due_date is not null and new.end_date='' then
        set new.end_date=new.due_date;
   end if;
      IF   new.end_date is not null and new.due_date='' then
        set new.due_date=new.end_date;
   end if;

END;
//


DELIMITER //

CREATE TRIGGER trig_2 before update
ON  &lt;table_name&gt; FOR EACH ROW
BEGIN 

   IF   new.due_date &lt;&gt;old.due_date then
        set new.end_date=new.due_date;
   end if;
      IF   new.end_date &lt;&gt; old.end_date then
        set new.due_date=new.end_date;
   end if;

END;
//


Hope it helps