Hi,

Before running the EXCEPTIONS INTO

1.The table contains duplicate records.
2.The status of constraint is not ENABLE VALIDATE (only then u can insert duplicate records)

After running the EXCEPTION INTO clause in ALTER statement

1.All the duplicate records will go in the exceptions table.
2.After deleting all these records from you main table you can bring the constraint to ENABLE VALIDATE status.

It has nothing to do with insertion of new records.

If you want that previous data to remain duplicate but from new transactions it should check by the constraint then bring the constraint into ENABLE NOVALIDATE state.

Hope its clear now.
Take Care,
Nishant.