How to unlock a database account (user)

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ALTER USER username account UNLOCK;

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Sqlplus/as SYSDBA
Alter user SYSTEM account unlock

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The default Scott user is locked out and can be logged on by unlocking it first.
Use the following statement to unlock Scott:alter user Scott account unlock;
You may be asked to change your password after unlocking: Alter user Scott identified by Tiger;
Re-login: Sqlplus Scott/tiger will be able to log in
Oracle locks and unlocks the user's command sql> conn/as SYSDBA is connected.
When the Scott user does not set the Tieger default password,
The method of locking the user is not logged on: sql> alter user test account lock; The user has changed.
-------test user logged into the database and failed.
C:\>sqlplus test/test error:ora-28000:the account is locked
Method of unlocking: sql> conn/as sysdba sql> alter user test account unlock; The user has changed.

From: http://blog.sina.com.cn/s/blog_6438b0e50100nrvp.html

How to unlock a database account (user)