How to lock and unlock oracle users using SQL commands?

We can lock/unlock oracle database users using the following SQL statement:

SQL >  alter user <username> account lock

Example:

SQL> conn sys/orcl@to_primary as sysdba
Connected.
SQL>
 ---To lock user
SQL> alter user mereba account lock;
 User altered.
 --To unlock user
SQL> alter user mereba account  unlock;
 User altered.