Flashback transcation query 能够查询事务对表所做的操作，通过UNDO SQL可以取消对事务所做的修改。查询FLASHBACK_TRANSACTION_QUERY这个数据字典表来获取字典事务ID的信息.
Flashback Transaction Query实际上是查询的数据字典flashback_transaction_query。可以根据flashback_transaction_query 的undo_sql列值返回数据以前版本
flashback_transaction_query 列说明：
SQL> desc flashback_transaction_query
Name Null? Type
----------------------------------------- -------- ----------------------------
XID RAW(8) --事务ID
START_SCN NUMBER --事务起始SCN，即第一个dml的SCN
START_TIMESTAMP DATE --事务其实时间戳,即第一个dm的时间戳
COMMIT_SCN NUMBER --提交事务时的SCN
COMMIT_TIMESTAMP DATE -- 提交事务时的时间戳
LOGON_USER VARCHAR2(30) --本次事务的用户
UNDO_CHANGE# NUMBER --撤销SCN
OPERATION VARCHAR2(32) --执行的dml操作：DELETE,INSERT,UPDATE,BEGIN,UNKNOWN
TABLE_NAME VARCHAR2(256) --dml更改的表
TABLE_OWNER VARCHAR2(32) --表的所有者
ROW_ID VARCHAR2(19) --修改行的ROWID
UNDO_SQL VARCHAR2(4000) -?-撤销dml的sql语句
--使用闪回事务查询前，必须启用重做日志流的其他日志记录，重做日志流与Log Miner使用的数据相同，只是接口不同。
例子：
SQL> sqlplus / as sysdba
SQL> alter database add supplemental log data;
Database altered.
SQL> alter database add supplemental log data (primary key) columns;
Database altered.
SQL> grant select any transaction to scott;
Grant succeeded.
SQL> update xyc_t1 set sal=9999 where empno=7902; --更改值sal=9999
1 row updated.
SQL> commit;
Commit complete.
SQL> select to_date(sysdate,'YYYY-MM-DD HH24:MI:SS') from dual;
TO_DATE(SYSDATE,'YY
-------------------
20210121 17:29:46
SQL> update xyc_t1 set sal=99999 where empno=7902; --更改值sal=99999
1 row updated.
SQL> commit;
Commit complete.
SQL> select to_date(sysdate,'YYYY-MM-DD HH24:MI:SS') from dual;
TO_DATE(SYSDATE,'YY
-------------------
20210121 17:30:17
select versions_startscn,versions_starttime,versions_endscn,versions_endtime,versions_xid,versions_operation,empno
from xyc_t1 versions between timestamp to_timestamp('20210121 17:29:46','YYYY-MM-DD HH24:MI:SS') and to_timestamp('20210121 17:30:17','YYYY-MM-DD HH24:MI:SS');
VERSIONS_STARTSCN VERSIONS_STARTTIME VERSIONS_ENDSCN VERSIONS_ENDTIME VERSIONS_XID V EMPNO
----------------- --------------------------------------------------------------------------- --------------- --------------------------------------------------------------------------- ---------------- - ----------
2170077 21-JAN-21 05.30.10 PM 0400130058040000 U 7902
2170077 21-JAN-21 05.30.10 PM 7902
7788
7698
--查询事务id
select start_scn,commit_scn,logon_user,operation,table_name,undo_sql
from flashback_transaction_query
where xid=hextoraw('0400130058040000');
--查出undo sql
SQL> update "SYS"."XYC_T1" set "SAL" = '9999' where ROWID = 'AAAVpSAABAAAW9hAAA';
1 row updated.
SQL> select * from xyc_t1;
select * from xyc_t1;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- -------------------- ------------------ ---------- ------------------- ---------- ---------- ----------
7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
7902 FORD ANALYST 7566 1981-12-03 00:00:00 9999 20
--返回到上一版本，即sal值为9999