Oracle误删除表数据后的恢复详解
测试环境：
SYSTEM:IBM AIX 5L Oracle Version:10gR2
1. undo_retention参数的查询与修改
使用show parameter undo命令查看当前的数据库参数undo_retention设置。
显示如下：
SQL> show parameter undo
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS2
undo_retention(保持力)，900单位是秒，即15分钟。
修改默认的undo_retention参数设置：
SQL> ALTER SYSTEM SET undo_retention=10800 SCOPE=BOTH;
System altered.
SQL> show parameter undo
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 10800
undo_tablespace string UNDOTBS2
undo_retention 10800，单位秒，即3小时。
2. oracle误删除表数据后的的快速恢复功能方法
2.1 方法一
通过oracle提供的回闪功能
exec dbms_flashback.enable_at_time(to_date('2011-04-15 08:21:00','yyyy-mm-dd hh24:mi:ss'));
set serveroutput on
DECLARE r_temp hr.job_history%ROWTYPE;
CURSOR c_temp IS SELECT * FROM hr.job_history;
BEGIN
OPEN c_temp;
dbms_flashback.disable;
LOOP
FETCH c_temp INTO r_temp;
EXIT WHEN c_temp%NOTFOUND;
insert into hr.job_history(EMPLOYEE_ID,JOB_ID,START_DATE,END_DATE) values (r_temp.EMPLOYEE_ID,r_temp.JOB_ID,r_temp.START_DATE,r_temp.END_DATE);
commit;
END LOOP;
CLOSE c_temp;
END;
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这种办法可以将删除的数据恢复到对应的表中，首先要保证该用户有执行dbms_flashback包的权限。
2.2 方法二
insert into hr.job_history
select * from hr.job_history as of timestamp to_timestamp('2011-04-15 08:20:00', 'yyyy-mm-dd hh24:mi:ss');
这种方法简单，容易掌握，功能和上面的一样，此处的时间为你误操作之前的时间，最好是离误操作比较近的，因为oracle保存在回滚保持段里的数据时间有一定的时间限制，这个限制由undo_retention 这个参数值决定。
查看FIRST_CHANGE#,NEXT_CHANGE#,FIRST_TIME
SQL> set pagesize 9999
SQL> col fscn for 999999999
SQL> col nscn for 999999999
SQL> select name,FIRST_CHANGE# fscn,NEXT_CHANGE# nscn,FIRST_TIME from v$archived_log;
当前的SCN为:
SQL> select dbms_flashback.get_system_change_number fscn from dual;
FSCN
----------
3435958
使用应用用户尝试闪回
SQL> connect username/password
Connected.
现有数据:
SQL> select count(*) from hs_passport;
COUNT(*)
----------
851998
创建恢复表：
SQL> create table hs_passport_recov as select * from hs_passport where 1=0;
Table created.
选择SCN向前恢复：
SQL> select count(*) from hs_passport as of scn 12929970422;
COUNT(*)
----------
861686
尝试多个SCN，获取最佳值（如果能得知具体时间，那么可以获得准确的数据闪回）
SQL> select count(*) from hs_passport as of scn &scn;
Enter value for scn: 12929941968
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12929941968
COUNT(*)
----------
861684
SQL> /
Enter value for scn: 12927633776
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12927633776
select count(*) from hs_passport as of scn 12927633776
*
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
SQL> /
Enter value for scn: 12929928784
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12929928784
COUNT(*)
----------
825110
SQL> /
Enter value for scn: 12928000000
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12928000000
select count(*) from hs_passport as of scn 12928000000
*
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
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最后选择恢复到SCN为12929941968的时间点
SQL> insert into hs_passport_recov select * from hs_passport as of scn 12929941968;
861684 rows created.
SQL> commit;
Commit complete.
数据恢复简单例子
在过去，如果用户误删/更新了数据后，作为用户并没有什么直接的方法来进行恢复，他们必须求助DBA来对数据库进行恢复，到了Oracle9i，这一难堪的局面有所改善。Oracle 9i中提供了一项新的技术手段--闪回查询，用户使用闪回查询可以及时取得误操作前的数据，并可以针对错误进行相应的恢复措施，而这一切都无需DBA干预。
3. 下面我们通过一个例子来具体说明闪回查询的用法
示例
3.1 使用闪回查询前必须确定下面两个参数：
UNDO_MANAGEMENT = AUTO
undo_retention = 10800;
这个时间可以随便设，它表示在系统中保留提交了的UNDO信息的时间，10800就是保留3小时，即180分钟。
3.2 使用闪回查询
SQL> conn /as sysdba
Connected.
SQL> drop user lsf cascade;
User dropped.
SQL> create user lsf identified by lsf;
User created.
SQL> grant connect,resource to lsf;
Grant succeeded.
SQL> grant execute on dbms_flashback to lsf;
Grant succeeded.
SQL> conn lsf/lsf
Connected.
SQL> create table T(id int, name varchar2(20));
Table created.
SQL> insert into T values(1,'lsf');
1 row created.
SQL> insert into T values(2,'lsf');
1 row created.
SQL> insert into T values(3,'lsf');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from T;
ID NAME
---------- ------------------------------------------------------------
1 lsf
2 lsf
3 lsf
SQL> set time on
10:12:50 SQL> delete from T where id=1;
1 row deleted.
10:13:02 SQL> commit;
Commit complete.
10:13:10 SQL> select * from T;
ID NAME
---------- ------------------------------------------------------------
2 lsf
3 lsf
10:13:18 SQL> execute