Oracle SYSDBA privilege

Question: I want to know what SYSDBA privilege can do. I know SYSDBA is SUPERSET of SYSOPER privilege, but what is the SYSDBA privilege?
Answer:  SYSDBA is like a role in the sense that it is granted, but SYSDBA is a special built-in privilege to allow the DBA full control over the database:

• Access to all data dictionary tables (dba views)

•  access to all v$ views and x$ structures

•  perform startup/shutdown commands

•  alter database: mount, open, back up, or change character set commands

•  create/drop database commands

•  create spfile commands

•  alter database commands

Granting SYSDBA privileges

Oracle creates three roles when you first create your database, CONNECT, RESOURCE and DBA.  When a use is granted SYSDBA, they are allowed to connect as SYSDBA within SQL*Plus (via the $ORACLE_HOME/bin/sqlplusexecutable).

connect sys/* as sysdba;

create user myuser identified by mypass;

grant sysdba to myuser;

If you intend to use OS authentication (identified externally or OPS$), we have the OSDBA role which is created when you install the Oracle executables.

The SYSDBA privilege is a special “global” privilege, grantable only when connected from SYS or SYSTEM, and you cannot see the roles within SYSDBA by querying the dba_role_privs and related system views.

The SYSDBA role (and the ability to connect via SYSDBA includes all system privileges (95 separate grants), the capability to grant those system privileges to others, and UNLIMITED TABLESPACE is granted in the same way as with the RESOURCE role.  

If the exp_full_database and imp_full_database roles have been created, the delete, execute and select_catalog_role roles are granted implicitly with the SYSDBA role (and hence the connect as SYSDBA command).

 How to connect as SYSDBA

In UNIX, you connect as sysdba thusly, being careful not to put the password on the UNIX prompt (where it can be seen):

root> sqlplus / 
SQL> connect myuser as sysdba password mypass

 In Windows, you connect from the DOS prompt:

C:\>sqlplus “sys as sysdba”

 But it’s never a good idea on a Windows server to include the password for a SYSDBA user outside of Oracle:

C:\>sqlplus “sys/my_password as sysdba”

 Prior to the connect xxx as sysdba syntax, Oracle offered an alternative mechanism called connect internal via granting a DBA role to give a user the equivalent of a SYSDBA connection, using an obsolete command executable called svrmgrl.