sys是Oracle數據庫中權限最高的帳號，具有create database的權限，而system沒有這個權限，sys的角色是sysdba，system的角色是sysoper。
其余就是他們兩個用戶共有的權限了：
startup/shutdown/dba兩個用戶都是可以管理的。
平時用system來管理數據庫就可以了。這個用戶的權限對於普通的數據庫管理來說已經足夠權限了。
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
