RMAN How to Unregister the Target Database from the Recovery Catalog

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Prior to release 10G, it was required to execute dbms_rcvcat.unregisterdatabase(db_key, db_id) from sqlplus to unregister a database from the recovery catalog (Ref. Note 1058332.6).

From 10G onwards, the process is simplified by introducing a new RMAN command to unregister the target database from the recovery catalog.

The syntax of the command to unregister the target database is:

                    rman> unregister database <database_name>;

                    rman> unregister database <database_name> noprompt;

where   <database_name>: Specifies the name of the target database that you are unregistering.

                    You do not have to specify db_name if RMAN is connected to the target database or if you have already set the DBID

   NOPROMPT       : Specifies that RMAN should not prompt for confirmation before unregistering the database.

Important points regarding the usage of this command:

    * Execute only at the RMAN prompt.

    * RMAN must be connected to the recovery catalog in which the target database is registered.

    * You can identify the database to unregister in one of three ways:

1)       Connect RMAN to the target database

                    Example:

                      rman TARGET SYS/oracle@test1 CATALOG rman/rman@catdb

                      RMAN> UNREGISTER DATABASE NOPROMPT;

2)       Provide the database_name argument to identify the database to unregister, if the database name is unique;

3)       Use SET DBID to identify the database if RMAN is not connected to the target database and the database_name is not unique in the recovery catalog.

        Example:

                      rman CATALOG rman/rman@catdb

                      RMAN>  SET DBID 1334531173;   # specifies test database by DBID

                     RMAN>  UNREGISTER DATABASE;

The command  "unregister database "  should be executed  only at the RMAN prompt.  This is a restriction to use this command.

Ref : 

How to Unregister the Target Database from the Recovery Catalog in 10G? [ID 252800.1]
Lost of Stored RMAN Scripts when Unregistering a Database [ID 100005.1]
How To Unregister An Inaccessible Database When Using RMAN [ID 246193.1]