SQL - MySQL Triggers

DELIMITER $$ CREATE TRIGGER trig_ins_dept_mng AFTER INSERT ON dept_manager FOR EACH ROW BEGIN DECLARE v_curr_salary int; SELECT MAX(salary) INTO v_curr_salary FROM salaries WHERE emp_no = NEW.emp_no; IF v_curr_salary IS NOT NULL THEN UPDATE salaries SET to_date = SYSDATE() WHERE emp_no = NEW.emp_no and to_date = NEW.to_date; INSERT INTO salaries VALUES (NEW.emp_no, v_curr_salary + 20000, NEW.from_date, NEW.to_date); END IF; END $$ DELIMITER ; --------------------------- Hi. I was reading the code in the section 'MySQL Triggers' and wondering why 'UPDATE salaries SET to_date = SYSDATE() WHERE emp_no = NEW.emp_no and to_date = NEW.to_date;' was used in the code. In the 'Salaries' table, I don't see any updated date(today's date) in the 'to_date' column. What's the function of this part of this code? It seems the whole code would work without it as well.   Thanks!