Trigger for Update particular column

CREATE TABLE MEMBER(

EID number,

ENAME VARCHAR2(30),

SAL number,

COMM number,

CHANGEDATE timestamp);

insert into member values(1,'James',2000,400,sysdate);

insert into member values(2,'Roy',3000,400,sysdate);

CREATE OR REPLACE TRIGGER MEMBER_UPDATE

BEFORE UPDATE OF SAL,COMM ON MEMBER

REFERENCING NEW AS NEW OLD AS OLD

FOR EACH ROW

BEGIN

:NEW.CHANGEDATE:=sysdate;

END;

/

select * from member;

update member set sal=2500 where EID=1;

commit;

select * from member;

update member set ENAME='Sunny' where EID=2;

commit;

select * from member;