The syntax to kill a session in oracle database is :

ALTER SYSTEM KILL SESSION ‘SID,SERIAL#’ IMMEDIATE;

EXAMPLE:

First get the sid and serial# of the session;

Here the session is executing the query SELECT * FROM DBACLASS;

Use the below query to get the sid and serial# of this sql query.

COL SQL_TEXT format a45
SQL>  SELECT a.sid,a.serial#,substr(b.sql_text,1,200) sql_text from v$sql b, 
     v$session a where a.sql_id=b.sql_id and  upper(b.sql_text)
     like '%DBACLASS%' and upper(b.sql_text) not like '%V$SQL%';  2  

       SID    SERIAL# SQL_TEXT
---------- ---------- ---------------------------------------------
	24	19329 select * from dbaclass


----Now kill session :

SQL>  alter system kill session '24,19329'  immediate;

System altered.