Security :: Oracle Audit Design?

Let us say I want to audit data updates, deletes on existing table EMP_TAB that has a few hundred thousands of records.I created a shadow table Emp_tab_audit and added few audit columns

Emp_tab (
Empno NUMBER NOT NULL,
Ename VARCHAR2(10),
Job VARCHAR2(9),

[code]...

I am mostly interested in UPDATES and DELETES but I decided to add INSERTS to have full history for each eomplyee in one table (audit schema) instead of querying two tables all the time (production table and audit table) to see the changes.

I created this AFTER INSERT, UPDATE, DELETE trigger.decided to copy the :NEW values for INSERT and UPDATE and :OLD values for DELETE. attached.

so when insert happens, the first audit row is created in EMP_TAB_AUDIT. update happens, the 2nd new row is created in EMP_TAB_AUDIT.

The problem I am facing is the old records that curently exist. If someone updates an old row I am copying the :NEW values so I won't have a copy of the :OLD values unless I create 2 ROWS (one for the old and one for the new).

Do you think I should copy all the hundreds of thousands of records to the AUDIT tables for this to work.

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CREATE OR REPLACE TRIGGER TRG_EMP_AUDIT
AFTER INSERT OR DELETE OR UPDATE ON EMP_TAB
FOR EACH ROW DECLARE
v_operation VARCHAR2(10) := NULL;

[code]...