restore 把文件还原回去；
recover 利用日志文件重做；
关键性的文件丢失和非关键性的文件丢失(system/undo之外的丢失)
1>
删除undo文件：
[oracle@oracle ~]$ rm /u01/oracle/oradata/jadl10g/undotbs01.dbf
[oracle@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Thu Nov 6 14:41:40 2014
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP, Data Mining Scoring Engine
and Real Application Testing options
SQL> conn scott/tiger ---此时连接没有报错，是由于undo已经缓存了，清除缓存；
Connected.
SQL> conn / as sysdba
Connected.
SQL> alter system flush shared_pool;
System altered.
SQL> alter system flush buffer_cache;
System altered.
SQL> alter system flush global context;
System altered.
SQL> conn scott/tiger ----连接scott用户出错，提示undo丢失
ERROR:
ORA-00604: error occurred at recursive SQL level 1
ORA-01116: error in opening database file 2
ORA-01110: data file 2: '/u01/oracle/oradata/jadl10g/undotbs01.dbf'
ORA-27041: unable to open file
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3
Warning: You are no longer connected to ORACLE.
SQL> conn / as sysdba
Connected.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP, Data Mining Scoring Engine
and Real Application Testing options
[oracle@oracle ~]$ rman target /
Recovery Manager: Release 10.2.0.5.0 - Production on Thu Nov 6 14:45:54 2014
Copyright (c) 1982, 2007, Oracle. All rights reserved.
RMAN> shutdown abort
using target database control file instead of recovery catalog
Oracle instance shut down
RMAN> startup mount
connected to target database (not started)
Oracle instance started
database mounted
Total System Global Area 599785472 bytes
Fixed Size 2098112 bytes
Variable Size 163580992 bytes
Database Buffers 427819008 bytes
Redo Buffers 6287360 bytes
RMAN> restore datafile 2;
Starting restore at 06-NOV-14
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=157 devtype=DISK
channel ORA_DISK_1: starting datafile backupset restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
restoring datafile 00002 to /u01/oracle/oradata/jadl10g/undotbs01.dbf
channel ORA_DISK_1: reading from backup piece /u01/oracle/flash_recovery_area/JADL10G/backupset/2014_11_06/o1_mf_nnndf_TAG20141106T135107_b5p32dhf_.bkp
channel ORA_DISK_1: restored backup piece 1
piece handle=/u01/oracle/flash_recovery_area/JADL10G/backupset/2014_11_06/o1_mf_nnndf_TAG20141106T135107_b5p32dhf_.bkp tag=TAG20141106T135107
channel ORA_DISK_1: restore complete, elapsed time: 00:00:07
Finished restore at 06-NOV-14
RMAN> recover database;
Starting recover at 06-NOV-14
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:01
Finished recover at 06-NOV-14
RMAN> alter database open;
database opened
*****采用此种恢复方法之后不需要重新备份 数据库，该方法可用于undo丢失或者系统表空间丢失。****
2>建立新的undo表空间，更改为新建的表空间，前提是能正确执行新建undo表空间的命令；
[oracle@oracle ~]$ rm /u01/oracle/oradata/jadl10g/undotbs01.dbf
[oracle@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Thu Nov 6 14:52:24 2014
Copyright (c) 1982, 2010, Ora