flashback query闪回数据

误删除了部分重要数据，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。