CREATE TABLE person (
fname VARCHAR2(15),
lname VARCHAR2(15));

CREATE TABLE audit_log (
o_fname   VARCHAR2(15),
o_lname   VARCHAR2(15),
n_fname   VARCHAR2(15),
n_lname   VARCHAR2(15),
chng_by   VARCHAR2(10),
chng_when DATE);

CREATE OR REPLACE TRIGGER referencing_clause
AFTER UPDATE
ON person
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
  INSERT INTO audit_log
  (o_fname, o_lname, n_fname, n_lname, chng_by, chng_when)
  VALUES
  (:OLD.fname, :OLD.lname, :NEW.fname, :NEW.lname, USER, SYSDATE);
END referencing_clause;
/

INSERT INTO person (fname, lname) VALUES ('Dan', 'Morgan');

SELECT * FROM person;
SELECT * FROM audit_log;

UPDATE person
SET lname = 'Dangerous';

SELECT * FROM person;
SELECT * FROM audit_log;

UPDATE person
SET fname = 'Mark', lname = 'Townsend';

SELECT * FROM person;
SELECT * FROM audit_log;