在进行数据库恢复的过程中,很多时候我们需要知道Oracle数据库的DBID,通常有以下几种方法可以获得数据库的DBID.

1.查询v$database获得

由于DBID在控制文件和数据文件中都存在记录,所以如果能够mount数据库就可以查询v$database视图获得. 

SQL> alter database mount;

Database altered.

SQL> select dbid from v$database;

      DBID
----------
3152029224

2.在nomount状态时

如果数据库配置了自动控制文件备份(Oracle9i),并且名称是缺省的,那么我们可以从自动备份文件获得DBID. 

[oracle@jumper dbs]$ cd $ORACLE_HOME/dbs
[oracle@jumper dbs]$ ll c-*
-rw-r----- 1 oracle dba 3375104 Dec 21 11:13 c-3152029224-20051221-00
-rw-r----- 1 oracle dba 3358720 Jan 21 14:03 c-3152029224-20060121-00
-rw-r----- 1 oracle dba 3358720 Jan 21 14:08 c-3152029224-20060121-01
这里的3152029224就是DBID。在10g中，使用Flash Recovery Area，则没有这个命名规则。
3.从自动备份中恢复

需要或缺DBID进行恢复通常是因为丢失了所有的控制文件.在恢复时会遇到错误.
[oracle@jumper dbs]$ rman target  /

Recovery Manager: Release 9.2.0.4.0 - Production

Copyright (c) 1995, 2002, Oracle Corporation.  All rights reserved.

connected to target database: conner (not mounted)

RMAN> restore controlfile from autobackup;

Starting restore at 05-FEB-06

using target database controlfile instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=11 devtype=DISK
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 02/05/2006 20:47:25
RMAN-06495: must explicitly specify DBID with SET DBID command 

如果存在自动备份,我们通常可以直接恢复控制文件,mount数据库之后就好办了: 
RMAN> restore controlfile from '/opt/oracle/product/9.2.0/dbs/c-3152029224-20051221-00';

Starting restore at 05-FEB-06

using channel ORA_DISK_1
channel ORA_DISK_1: restoring controlfile
channel ORA_DISK_1: restore complete
replicating controlfile
input filename=/opt/oracle/oradata/conner/control01.ctl
output filename=/opt/oracle/oradata/conner/control02.ctl
output filename=/opt/oracle/oradata/conner/control03.ctl
Finished restore at 05-FEB-06
  4.直接从幸存的文件中读取

由于DBID存在于数据文件及控制文件中,所以我们可以通过PL/SQL程序直接从文件中读取: 
SQL> select eygle.get_dbid('/opt/oracle/oradata/conner','user02.dbf') from dual;

EYGLE.GET_DBID('/OPT/ORACLE/OR
------------------------------
3152029224

SQL> select dbid from v$database;

DBID
----------
3152029224
 其实更简单的，用BBED就好了。
  这种方法仅为测试兴趣所致,不被推荐.