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