[oracle@zhs10g ~]$ rman catalog=ctlg/ctlg@bcatalog
Recovery Manager: Release 10.2.0.4.0 - Production on Fri Aug 24 01:58:16 2012
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to recovery catalog database
RMAN> unregister database utf10g;
database name is "utf10g" and DBID is 1585746538
Do you really want to unregister the database (enter YES or NO) yes
database unregistered from the recovery catalog
RMAN>
如果恢复目录中有多个已相同名称注册的数据库时，就需要知道希望取消注册的数据库的DBID。然后在run代码块中运行unregister database命令，同时使用set dbid命令。如：
run
{
set dbid 1585746538;
unregister database UTF10G NOPROMPT;
}