2.

（1）sys -- sysdba
（4）sysdba比sysoper多了一个create database的权限
3.
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。
SYSOPER
ARCHIVELOG and RECOVERY
CREATE SPFILE

SYSDBA
ALTER DATABASE OPEN/MOUNT/BACKUP
ALTER DATABASE: open, mount, back up, or change character set
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
CREATE SPFILE
This privilege allows a user to perform basic operational tasks, but without the ability to look at user data Perform STARTUP and SHUTDOWN operations
（2）startup/shutdown/dba管理两个都能做
ARCHIVELOG and RECOVERY
Includes the RESTRICTED SESSION privilege
system --sysoper
1.
Includes the RESTRICTED SESSION privilege
CREATE DATABASE
Perform STARTUP and SHUTDOWN operations
Effectively, this system privilege allows a user to connect as user SYS.
（3）sys拥有数据字典(dictionay),或者说dictionay属于sys schema