Oracle Flashback Query 闪回数据

误删除了Oracle部分重要数据，已提交，需要恢复。首先尝试Flashback Query闪回数据。

数据库运行在归档模式，首先确认数据库的SCN的变化：

SQL> col fscn for 999999999999999999999 SQL> col nscn for 999999999999999999999 SQL> select name,first_change# fscn,next_change# nscn, first_time from v$archived_log;

NAME                                            FSCN    NSCN FIRST_TIME ----------------------------------------------------------------------------- ----------- ----------- ------------------ /u01/app/oracle/fast_recovery_area/CDB/CDB/archivelog/2018_05_28/o1_mf_1_3_fj      1547949    1550763 2018:05:2816:37:41 qj6z9t_.arc

/u01/app/oracle/fast_recovery_area/CDB/CDB/archivelog/2018_05_28/o1_mf_1_4_fj      1550763    1551171 2018:05:2816:42:07 qjsm3t_.arc

/u01/app/oracle/fast_recovery_area/CDB/CDB/archivelog/2018_05_28/o1_mf_1_5_fj      1551171    1551255 2018:05:2816:52:03 qjwkog_.arc

/u01/app/oracle/fast_recovery_area/CDB/CDB/archivelog/2018_05_28/o1_mf_1_6_fj      1551255    1551654 2018:05:2816:53:37 qjxycd_.arc

获取当前的SCN： SQL> select dbms_flashback.get_system_change_number  fscn from dual;

          FSCN ----------------------           1551702       

使用应用用户尝试闪回： SQL> conn c##scott/tiger Connected.

现有数据： SQL> select count(*) from emp1;

  COUNT(*) ----------     0

创建恢复表： SQL> create table emp1_recov as select * from emp1 where 1=0;

Table created.

根据业务提供的大致误操作时间，结合V$ARCHIVED_LOG视图，选择适当SCN向前执行闪回查询： SQL> select count(*) from emp1 as of scn 1551171; select count(*) from emp1 as of scn 1551171                     * ERROR at line 1: ORA-01466: unable to read data - table definition has changed

尝试多个SCN，获取最佳值（能知道具体时间，那么可以获取准确的数据恢复）：

SQL> select count(*) from emp1 as of scn 1551255;

  COUNT(*) ----------     14

SQL> select count(*) from emp1 as of scn 1551200; select count(*) from emp1 as of scn 1551200                     * ERROR at line 1: ORA-01466: unable to read data - table definition has changed

SQL> select count(*) from emp1 as of scn 1551233; select count(*) from emp1 as of scn 1551233                     * ERROR at line 1: ORA-01466: unable to read data - table definition has changed

SQL> select count(*) from emp1 as of scn 1551244;

  COUNT(*) ----------     14

最后选择恢复到SCN为1551244的时间点，代码如下： SQL> insert into emp1_recov select * from emp1 as of scn 1551244;

14 rows created.

SQL> commit;

Commit complete.

由业务人员通过emp1_recov表确认，向当前表补回误删除的数据，至此闪回恢复成功。没有闪回特性的话，需要通过物理备份执行不完全恢复，或者找出足够及时的逻辑备份来进行恢复，其过程都可能是极其复杂的。