kill session

SQL> drop user xxxxx cascade;
drop user xxxxx cascade
*
ERROR at line 1:ORA-01940: cannot drop a user that is currently connected
SQL> select sid, serial# from v$session where username = 'xxxxx';
SID SERIAL#
----- ------------
268 1268
315 1223

SQL> Alter user xxxxx account lock;
SQL> alter system kill session '268,1268';
System altered.

SQL> alter system kill session '315,1223';
System altered.

SQL> drop user xxxxx cascade;
User dropped.