有些时候,不小心删除了一些需要的表,而且数据库不能停止,只能一直运行下去,这样的话很麻烦
下面介绍的方法就是删除表后通过时间戳后者scn找回删除的数据
模拟实验环境:
创建一个新表
SQL> create table www as select * from hr.employees;
Table created.
查看新表是否有数据
SQL> select count(*) from www;
COUNT(*)
----------
107
查看当前的时间,这里时间或者scn有一个就行。后面会有通过scn恢复的案例
SQL> select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;
TO_CHAR(SYSDATE,'YY
-------------------
2017-11-13 17:34:45
查找时间戳之前是否有数据
SQL> select count(*) from www as of timestamp to_timestamp('2017-11-13 17:30:45','yyyy-mm-dd hh24:mi:ss');
select count(*) from www as of timestamp to_timestamp('2017-11-13 17:30:45','yyyy-mm-dd hh24:mi:ss')
*
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
查询下这个时间段的数据是存在的
SQL> select count(*) from www as of timestamp to_timestamp('2017-11-13 17:34:45','yyyy-mm-dd hh24:mi:ss');
COUNT(*)
----------
107
删除表:
SQL> delete from www;
107 rows deleted.
SQL> commit;
Commit complete.
查看www表是没有数据的
SQL> select * from www;
no rows selected
当前时间查看也是没有数据了
SQL> select count(*) from www as of timestamp to_timestamp('2017-11-13 17:37:45','yyyy-mm-dd hh24:mi:ss');
COUNT(*)
----------
0
我们需要这样做,查看下删除之前的时间,根据删除之前的时间戳找到www表中的数据
SQL> select count(*) from www as of timestamp to_timestamp('2017-11-13 17:34:45','yyyy-mm-dd hh24:mi:ss');
COUNT(*)
----------
107
查看时间戳发现有数据存在,说明数据可以恢复
SQL> insert into www select * from www as of timestamp to_timestamp('2017-11-13 17:34:45','yyyy-mm-dd hh24:mi:ss');
107 rows created.
SQL> commit;
Commit complete.
数据恢复成功
SQL> select count(*) from www;
COUNT(*)
----------
107
同理,scn也是可以恢复的
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
3698087
SQL> create table www as select * from hr.employees;
Table created.
SQL> select count(*) from www;
COUNT(*)
----------
107
查看创建表之后的scn
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
3698135
SQL> delete from www;
107 rows deleted.
表中的数据已经没有了
SQL> select count(*) from www;
COUNT(*)
----------
0
SQL> commit;
Commit complete.
通过创建表之后的scn号来查询后,找到了相关数据
SQL> select count(*) from www as of scn 3698135;
COUNT(*)
----------
107
将数据插入到表中即可
SQL> insert into www select * from www as of scn 3698135;
107 rows created.
SQL> commit;
Commit complete.
完成恢复。
同理scn和时间戳可以互相转换
scn-->timestamp
SQL> select scn_to_timestamp(3698087) scn from dual;
SCN
---------------------------------------------------------------------------
13-NOV-17 05.43.11.000000000 PM
timestamp-->scn
SQL> select timestamp_to_scn(to_timestamp('2017-11-13 17:34:45','yyyy-mm-dd hh24-mi-ss')) scn from dual;
SCN
----------
3697660
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