플래쉬백 트랜젝션 쿼리 실습해보고 있는데요.

아래와 같이 SQL치면 UNDO_SQL 값이 안나옵니다. 왜 안나오는걸끼요?

SQL>SELECT UNDO_SQL, TABLE_NAME, START_SCN FROM flashback_transaction_query WHERE TABLE_NAME='MBR';

UNDO_SQL                       TABLE_NAME  START_SCN
-------------------------------- -------------- --------------------
                                        MBR           1192110
                                        MBR           1193134
                                        MBR           1197564
                                        MBR           1192022
                                        MBR           1192022
                                        MBR           1192022

6 rows selected.

SQL>