解锁语法：
alter user user_name identified by password account unlock;例如： 解锁，用户：scott，密码：tiger
SYS@ORA11GR2> conn scott/tiger
ERROR:
ORA-28000: the account is locked
Warning: You are no longer connected to ORACLE.SYS@ORA11GR2> alter user scott identified by tiger account unlock;
User altered.
SYS@ORA11GR2> conn scott/tiger
Connected.
SCOTT@ORA11GR2>