1.
SYS用戶具有DBA權限，並且擁有SYS模式，只能通過SYSDBA登陸數據庫。是Oracle數據庫中權限最高的帳號
SYSTEM具有DBA權限。但沒有SYSDBA權限。平常一般用該帳號管理數據庫就可以了。
2.
（1）sys -- sysdba
system --sysoper
（2）startup/shutdown/dba管理兩個都能做
（3）sys擁有數據字典(dictionay),或者說dictionay屬於sys schema
（4）sysdba比sysoper多了一個create database的權限
3.
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
