1.

SYS用户具有DBA权限，并且拥有SYS模式，只能通过SYSDBA登陆数据库。是Oracle数据库中权限最高的帐号

SYSTEM具有DBA权限。但没有SYSDBA权限。平常一般用该帐号管理数据库就可以了。

2.

（1）sys -- sysdba

system --sysoper

（2）startup/shutdown/dba管理两个都能做

（3）sys拥有数据字典(dictionay),或者说dictionay属于sys schema

（4）sysdba比sysoper多了一个create database的权限

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