Drop a Target Database Using RMAN in Oracle 10g.

Beginning with Oracle 10g Release 1 onwards, A database can be dropped
by executing few simple statements.

With this method all datafiles, controlfiles, Redo log files, Spfile, Archived
Redo log files, backups will be dropped along with the target database.

So, lets begin

$ export ORACLE_SID=orcl
$ sqlplus

Username: /  as  sysdba

SQL> shutdown immediate

SQL> startup mount exclusive

SQL> alter system enable restricted session;

SQL> exit

$ rman target=/

RMAN> drop database including backups;