Assume that a user is locked because he or she
belongs to a login policy with locked=ON.
To unlock such a user, assign him or her to a login policy where
option locked=OFF.
A user can also be locked if he/she has exceeded
the max_failed_login_attempts or max_days_since_login.
To unlock such a user, use a statement like the following:
ALTER USER john RESET LOGIN POLICY
The preceding statement is semantically equivalent to ALTER
USER userid LOGIN POLICY current-policy-for-user.