1 Database Administration

2 Objectives  Understand, create, and drop views  Grant and revoke users’ privileges  Understand and obtain information from the system catalog

3 Views  Base tables Existing, permanent tables in a relational database  View A derived table where data is derived from a base table User interacts with the view View provides security

4 View Benefits  Views provide data independence  Different users can view the same data in different ways because each user has their own view  It can contain only those columns required by a given user Greatly simplifies user perception of database Furnishes a measure of security since user as access to data contained only in their view

5 Views  A view is defined by creating a defining query (SQL command that indicates the rows and columns that will appear in the view)  The formulation of the view definition is: CREATE AS  The defining query can be any valid SQL query  Define a view named HOUSEWARES that consists of the part number, part description, units on hand, and unit price of all parts in item class HW

6 Joins  In general, views that involve joins of base tables can cause problems at update  If two base tables have the same primary key and the primary key is used as the join column, updating the database is not a problem

7 DROP View Command  Deletes a view definition only  Table and data on which view is based still exists

8 Security  Security is the prevention of unauthorized access to the database  Two security mechanisms Views GRANT command

9 GRANT and REVOKE Commands  Grant different privileges to users and revoke them later, if necessary: Ability to select rows from a table Insert new rows Update existing rows  GRANT TO  REVOKE FROM

10 Privileges  Privileges that can be granted are SELECT UPDATE DELETE INSERT INDEX  For a user to pass the privilege on to others the database administrator must use GRANT statement and include WITH GRANT OPTION

11 GRANT Command  User Jones must be able to retrieve data from the SALES_REP table GRANT SELECT ON SALES_REP TO JONES;  Users Smith and Brown must be able to add new parts to the PART table. GRANT INSERT ON PART TO SMITH, BROWN;

12 GRANT Command  User Thomas must be able to change the structure of the CUSTOMER table GRANT ALTER ON CUSTOMER TO THOMAS;  User Wilson must have all privileges for the SALES_REP, CUSTOMER, and ORDERS tables GRANT ALL ON SALES_REP, CUSTOMER, ORDERS TO WILSON;

13 REVOKE Command  User Jones is no longer allowed to retrieve data from the SALES_REP table REVOKE SELECT ON SALES_REP FROM JONES;

14 Comprehensive Example  Allow sales rep number 03 (Mary Jones) to access any data concerning the customers she represents, but do not permit her to access data concerning any other customer CREATE VIEW SLSR3CST AS SELECT * FROM CUSTOMER WHERE SLSREP_NUMBER = ’03’ GRANT SELECT ON SLSR3CST TO MARY JONES;

15 The System Catalog  Information concerning tables known to the DBMS is kept in the system catalog, or the data dictionary  System catalog contains tables USER_TABLES (DBA_TABLES) USER_TAB_COLUMNS (DBA_TAB_COLUMNS) USER_VIEWS (DBA_VIEWS)  System catalog is a relational database  Users need special privileges to view the data in the system catalog

16 System Catalog Example  List the name of every table for which the owner (creator of the table) is PRATT SELECT TABLE_NAME FROM DBA_TABLES WHERE OWNER = ‘PRATT’;  List the name of every view whose owner is PRATT SELECT VIEW_NAME FROM DBA_VIEWS WHERE OWNER = ‘PRATT’;

17 Summary  A view is a pseudotable whose contents are derived form data in existing base tables whenever users attempt to access the view  To define a view, use the CREATE VIEW statement This statement includes a defining query that describes the portion of the database included in the view When a user retrieves data from the view, the query entered by the user is merged with the defining query, producing the query that SQL actually executes

18 Summary  Views provide data independence, allow database access control, and simplify the database structure for users  You cannot update views that involve statistics and views with joins of non-primary key columns In this case you must make all updates to the base table  Use the DROP VIEW command to delete a view  Use the GRANT command to give users access privileges to various portions of the database  Use the REVOKE command to terminate previously granted privileges

19 Summary  The DBMS maintains information about the tables, columns, indexes, and other system elements in the system catalog Information about tables is kept in the SYSTABLES table, information about columns is kept in the SYSCOLUMNS table, and information about views is kept in the SYSVIEWS table In Oracle these same tables are named DBA_TABLES, DBA_TAB_COLUMNS, and DBA_VIEWS  Use the SELECT command to obtain information from the system catalog  The DBMS updates the system catalog continuously; users do not update the catalog directly