Differences between SYS, SYSTEM, DBA, and SYSDBA

Differences between SYS and SYSTEM, DBA and SYSDBA: SYS and SYSTEM: 1. the role of sys is sysdba system and sysoper 2. sys has the create database permission. system does not have this permission. 3. sys can create and modify the base table and view of the data dictionary. system cannot create the base table and view of the data dictionary. it cannot be modified. 4. sys and system both have dba permissions. Using the QQ Group as a metaphor, sys is equivalent to a group master, and system is equivalent to a group administrator. DBA and SYSDBA: SYSDBA is not a permission. When a user logs into the database as SYSDBA, the login user will change to SYS. You can log on as SYSDBA to open the database, close the database, create SPFILE, and restore the database. These are not implemented by the DBA role. SYSDBA is the system permission and DBA is the user object permission; SYSDBA manages Oracle instances. Its existence does not depend on the full startup of the entire database. As long as the instance is started, it already exists. The DBA role has a foundation only after the database is opened or the entire database is fully started. (the creation process of the oracle service is: Create an instance, start an instance, and create a database: instance start-load database-Open Database) DBA is a set of role corresponding to the operation permissions on objects in the Oracle instance, SYSDBA is a conceptual role that represents the identity used for logon authentication. In addition, DBA is an object in Oracle. Like Role and User, DBA is a physical object that actually exists in Oracle. SYSDBA is a conceptual operation object, it does not exist in Oracle Data.