Canceling the Transaction
While a transaction is in progress, some type of error checking is usually performed to determine whether it is executing successfully. You can undo your transaction even after successful completion by issuing the ROLLBACK statement, but it must be issued before a COMMIT. The ROLLBACK statement must be executed from within a transaction. The ROLLBACK statement rolls the transaction back to its beginning; in other words, the state of the database is returned to what it was at the transaction's beginning. The syntax for this command using Oracle is the following:
ROLLBACK [WORK] [ TO [SAVEPOINT] savepoint | FORCE 'text' ]
As you can see, this command makes use of a transaction savepoint. We discuss this technique later ...