Oracle puts locks while performing any DDL or DML operation on oracle tables.When table locks is present on any tables in Oracle we cannot run DDL on those tables.
Some of the locks automatically set by oracle are RS and RX Locks.
SELECT … FOR UPDATE execution results in RS (row share) table lock. When you execute an INSERT, UPDATE or DELETE Oracle puts RX (row exclusive) table lock.
We have to kill the session which holds the lock in order to execute further operations. Follow the below steps to kill the session and forcibly unlock the table.
Let’s assume that 'EMP' table is locked,