一. 安装是用户管理：
sqlplus /nolog;
connect /as sysdba;
alter
user sys identified by change_on_install;
alter user system
identified by manager;
alter user scott identified by tiger;
（默认scott锁定）(scott用户中有emp
dept等表)
alter user scott account unlock;
二. Oracle常用命令：
show user;（查看当前用户）
connect sys/change_on_install as
sysdba;（切换sys用户）
或connect sys/change_on_install as sysoper;（切换sys用户
）
connect system/manager;
connect scott/tiger;