sys是Oracle数据库中权限最高的帐号，具有create database的权限，而system没有这个权限，sys的角色是sysdba，system的角色是sysoper。
其余就是他们两个用户共有的权限了：
startup/shutdown/dba两个用户都是可以管理的。
平时用system来管理数据库就可以了。这个用户的权限对于普通的数据库管理来说已经足够权限了。
SYSDBA
Perform STARTUP and SHUTDOWN operations
ALTER DATABASE: open, mount, back up, or change character set
CREATE DATABASE
CREATE SPFILE
ARCHIVELOG and RECOVERY
Includes the RESTRICTED SESSION privilege
Effectively, this system privilege allows a user to connect as user SYS.
SYSOPER
Perform STARTUP and SHUTDOWN operations
CREATE SPFILE
ALTER DATABASE OPEN/MOUNT/BACKUP
ARCHIVELOG and RECOVERY
Includes the RESTRICTED SESSION privilege
This privilege allows a user to perform basic operational tasks, but without the ability to look at user data