1. System Administration Accounts privileges, users and roles

2. What Is a User Account?
A user account is identified by a user name and defines the user's attributes, including the following:
Password for database authentication
Privileges and roles
Default tablespace for database objects
Default temporary tablespace for query processing work space

3. What Is the Relation of a User Account and a Schema?
User accounts and schemas have a one-to-one relation.
When you create a user, you are also implicitly creating a schema for that user. A schema is a logical container for the database objects (such as tables, views, triggers, and so on) that the user creates.
The schema name is the same as the user name, and can be used to unambiguously refer to objects owned by the user.

4. What Are Internal User Account?
An internal user account is a system predefined user account. Oracle 11g comes with a number of internal accounts:
SYSTEM - This is the user account that you log in with to perform all administrative functions other than starting up and shutting down the database. SYSTEM is automatically created when you install the server. It's password is the one you specified during the installation process.
SYS - This is another user account automatically created when you install the server. It's password is the one you specified during the installation process. All base tables and views for the database data dictionary are stored in the SYS schema. So avoid log in as user SYS as much as possible to reduce the risk of damaging those important data objects. User SYSTEM is preferred for all administrative tasks except starting up and shutting down.
Other internal user accounts - Other special user accounts are predefined for special purposes. For example, CTXSYS is a special user account used by the Oracle Text product.
Public account?

5. How To List All User Accounts?
User accounts can be accessed through a system view called ALL_USERS. A simple SELECT statement can be used to get a list of all user accounts.

6. How To Create a New User Account?
If you want to create a new user account, you can log in as SYSTEM and use the CREATE USER command as shown in the following example:
CREATE USER DEV IDENTIFIED BY developer ACCOUNT UNLOCK;

7. How To Change User Password?
If you want to change a user's password, you can log in as SYSTEM and use the ALTER USER command as shown in the following example:
ALTER USER DEV IDENTIFIED BY beginner;

8. How To Delete a User Account?
If you want to delete a user account and its associated schema, you can log in as SYSTEM and use the DROP USER command as shown in the following example:
DROP USER DEV CASCADE;
Note that CASCADE tells the server drop the associated schema.

9. What is a privilege? A privilege is a right
to execute an SQL statement or to access another user's object.
A privileges can be assigned to a user or a role
The set of privileges is predefined and fixed, but grantable and revocable.

10. Two Types of Privileges
 System Privileges
System Privileges are normally granted by a DBA to users. Examples of system privileges are CREATE SESSION, CREATE TABLE, CREATE USER etc.
Usually about DDL
System privileges are privileges that do not relate to a specific schema or object.
Object privileges
Object privileges means privileges on objects such as tables, views, synonyms, procedure. These are granted by owner of the object.
Usually about DML.
Owner already create an object, he can further decide who can manipulate it.
Create index is not a privilege (subtle, do not need to know, you will see it why when you are a DBA.)

11. A List of Object Privileges are granted by an owner
 ALTER  
Change the table definition with the ALTER TABLE statement.  
DELETE  
Remove rows from the table with the DELETE statement. You must grant the SELECT privilege on the table along with the DELETE privilege. 
INDEX  
Create an index on the table with the CREATE INDEX statement.  
INSERT  
Add new rows to the table with the INSERT statement.  
REFERENCES  
Create a constraint that refers to the table. You cannot grant this privilege to a role.  
SELECT  
Query the table with the SELECT statement.  
UPDATE  
Change data in the table with the UPDATE statement.  You must grant the SELECT privilege on the table along with the UPDATE privilege

12. Suppose you want to grant all privileges on employee table to robit
Suppose you want to grant all privileges on employee table to robit. Then
grant  all on employee to robi;
Suppose you want to grant select privilege on employee to all other users of the database. Then
grant select on employee to public;

13. Column level priviledges
As the owner of a table, you can control at column level at which you specify which columns are manipulatable by other schema owners.
Suppose you want to grant update and insert privilege on only certain columns not on all the columns then include the column names in grant statement.
For example you want to grant update privilege on ename column only and insert privilege on empno and ename columns only. Then give the following statement
  grant update (ename),insert (empno, ename)  on emp to sami;
 To grant select statement on emp table to sami and to make sami be able further pass on this privilege you have to give WITH GRANT OPTION clause in GRANT statement like this.
  grant select on emp to sami with grant option;

14. Subtle issues
Owner of a table can always create indexes on it, this is Not a privilege can be revoked by admin.
But owner can give create index priviledge to other users to allow them to create index on his tables.
Also, admin can do is to grant create any index to a user to allow him to create any index in any user’s schema.

15. Data Control Language (DCL) Statements
Data Control Language Statements are used to grant privileges on tables, views, sequences, synonyms, procedures to other users or roles.
 The DCL statements are
GRANT          :Use to grant privileges to other users or roles.
REVOKE       :Use to take back privileges granted to other users and roles.

16. What Privilege Is Needed for a User to Connect to Oracle Server?
Oracle deny connection to users who has no CREATE SESSION privilege. Try the following tutorial exercise, you will find out how Oracle denies connection:
CREATE USER DEV IDENTIFIED BY developer ACCOUNT UNLOCK;
user DEV lacks CREATE SESSION privilege; logon denied Oracle error message is pretty clear.

17. How To Revoke CREATE SESSION Privilege from a User?
If you take away the CREATE SESSION privilege from a user, you can use the REVOKE command as shown in the following example script:
REVOKE CREATE SESSION FROM dev;

18. Privileges
A privilege is a right to execute an SQL statement or to access another user’s object.
System privileges
Object privileges
A privilege can be assigned to a user a role

19. Granting Oracle System Level Privileges
The grant command is used to grant system level privileges. System level privileges are those privileges that you need to actually do something on the system.

20. WITH ADMIN OPTION
Sometime you want to grant privileges to users and have them be able to grant those privileges to other users.
When this is the case, we include the with admin keyword in the grant command. When this keyword is used, it will allow the user granted the privilege to grant that privilege to other users. Here is an example of the usage of the with admin option keyword.
GRANT CREATE ANY INDEX TO Robert WITH ADMIN OPTION;

21. What Privilege Is Needed for a User to Create Tables?
To be able to create tables in a user's own schema, the user needs to have the CREATE TABLE privilege, or the CREATE ANY TABLE privilege, which is more powerful, and allows the user to create tables in other user's schema.

22. How To Assign a Tablespace to a Users?
When you create a new user, Oracle will assign the SYSTEM tablespace to the user by default.
If you want to change this, you can assign a different table space to a user using the ALTER USER command.

23. How To Find Out What Privileges a User Currently Has?
Privileges granted to users are listed in two system views:
DBA_SYS_PRIVS
USER_SYS_PRIVS.
You can find out what privileges a user currently has by running a query on those views as shown in the tutorial exercise below:
SELECT username, privilege FROM USER_SYS_PRIVS;

24. LISTING INFORMATION ABOUT PRIVILEGES
To see which table privileges are granted by you to other users.
SELECT * FROM USER_TAB_PRIVS_MADE
To see which table privileges are granted to you by other users 
SELECT * FROM USER_TAB_PRIVS_RECD;
To see which column level privileges are granted by you to other users. 
SELECT * FROM USER_COL_PRIVS_MADE
 To see which column level privileges are granted to you by other users
SELECT * FROM USER_COL_PRIVS_RECD;
To see which privileges are granted to roles
SELECT * FROM USER_ROLE_PRIVS;

25. What Is a User Role?
A user role is a group of privileges. Privileges are assigned to users through user roles. You create new roles, grant privileges to the roles, and then grant roles to users.

26. ROLES
A role is a designed for a category users who share a group of Privileges.
A role is very handy in managing privileges, Particularly in such situation when number of users should have the same set of privileges. For example you have four users :Sami, Scott, Ashi, Tanya in the database.
To these users you want to grant select ,update privilege on emp table, select,delete privilege on dept table. To do this first create a role by giving the following statement  
create role clerks
Then grant privileges to this role.
  grant select,update on emp to clerks;
grant select,delete on dept to clerks;
 Now grant this clerks role to users like this
  grant clerks to sami, scott, ashi, tanya ;
 Now Sami, Scott, Ashi and Tanya have all the privileges granted on clerks role.
 Suppose after one month you want grant delete on privilege on emp table all these users then just grant this privilege to clerks role and automatically all the users will have the privilege.
  grant delete on emp to clerks;
 If you want to take back update privilege on emp table from these users just take it back from clerks role.
  revoke update on emp from clerks;
 To Drop a role
Drop role clerks;

27. What Are the System Predefined User Roles?
Oracle 11g comes with 3 predefined roles:
CONNECT - Enables a user to connect to the database. Grant this role to any user or application that needs database access.
RESOURCE - Enables a user to create certain types of schema objects in his own schema. Grant this role only to developers and to other users that must create schema objects. This role grants a subset of the create object system privileges.
DBA - Enables a user to perform most administrative functions, including creating users and granting privileges; creating and granting roles; creating and dropping schema objects in other users' schemas; and more. It grants all system privileges, but does not include the privileges to start up or shut down the database. It is by default granted to user SYSTEM.

28. As a DBA, the best and most secure practice to grant privileges is to always grant privileges with caution and give Oracle users only what they need.
As a schema owner, grant privileges to other users with caution and give them only what they need within your grantable power.

29. Some users, but hopefully only one or two, should have the SYSDBA and/or SYSOPER privileges.
This can be determined from the V$PWFILE_USERS view. This will tell you which Oracle users have the above privileges.

30. Be careful!
Depending on versions of Oracles, you may get different group of privileges for different default roles. For example, connect is a role that has dramatically different default priviledges between 9i and 10i.

31. System privileges