对scott账户锁定、解锁及修改密码
alter user soctt account lock; // 把 scott用户锁定
alter user scott account unlock;//把scott用户解锁
alter user scott identified by scott;//修改scott用户密码为 scott,scott用户默认密码为 tiger
alter user scott account unlock;//把scott用户解锁
alter user scott identified by scott;//修改scott用户密码为 scott,scott用户默认密码为 tiger