How to drop database manually, without using Database Configuration Assistant(DBCA)

Before proceed for entire database deletion, kindly consider full database backup for your future reference, if required.

Connect to target database with sys user, and issue following query to check database mode:

[oracle@testserver ~]$ sqlplus / as sysdba
SQL> select open_mode,name from v$database;
OPEN_MODE            NAME
-------------------- ---------
READ WRITE           BLADE2

Normally shutdown your database:

SQL> shut immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.

startup your database in mount mode with exclusive restrict, as follows:

SQL> startup mount exclusive restrict;
ORACLE instance started.
Total System Global Area 1.0088E+10 bytes
Fixed Size 2215984 bytes
Variable Size 5704257488 bytes
Database Buffers 4362076160 bytes
Redo Buffers 19640320 bytes
Database mounted.

Database is in mount mode:

SQL> select open_mode,name from v$database;
OPEN_MODE            NAME
-------------------- ---------
MOUNTED              BLADE2

Issue following SQL command in order to drop database, this will drop entire database with datafiles, control files and log files,etc.

SQL> drop database;
Database dropped.
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL>

Database dropped successfully.