SYSDBA:
The SYS user is automatically granted the SYSDBA privilege upon installation. When you log in as user SYS, you must connect to the database as SYSDBA. Connecting as a SYSDBA user invokes the SYSDBA privilege.
Sysdba has all rights to do any thing on the database.
SYSOPER:
Sysoper doesn’t have some privileges , they are
- Change character set
2.Create database
3.Drop database
4.ALTER DATABASE RECOVER (Complete recovery only. Any form of incomplete recovery, such as UNTIL TIME|CHANGE|CANCEL|CONTROLFILE requires connecting as SYSDBA.)
SYSTEM:
This account can perform all administrative functions except the following:
1.Backup and recovery
2.Database upgrade
When you connect with SYSDBA or SYSOPER privileges, you connect with a default schema, not with the schema that is generally associated with your user name. For SYSDBA this schema is SYS; for SYSOPER the schema is PUBLIC.
