SQL & PL/SQL :: Update In Employee Table?

Employee Table
==============
create table empoyee (
empno number,
sal number)
insert into employee(empno,sal) values (1, 200);

[code]...

If we make any update in Employee table for his/her salary, before update, that record should be inserted into EmployeeHist table and history will continue to build. Employee Table should have only current salary.If we change sal for emplyee # 1 from 200 to 800 then original current record in employee table will be inserted into employeehist table like

empsno = 1
empno =1
sal=200
last_update=sysdate