1. Chapter 6 Database Administration

2. Objectives Understand, create, and drop views
Recognize the benefits of using views
Grant and revoke users' database privileges
Understand the purpose, advantages, and disadvantages of using an index

3. Objectives Create, use, and drop an index
Understand and obtain information from the system catalog
Use integrity constraints to control data entry

4. Introduction Database administration Database administrator
The process of managing a database
Database administrator
A person or an entire group charged with managing the database

5. 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

6. Views A view is defined by creating a defining query
A defining query is a SQL command that indicates the rows and columns that will appear in the view
To create a view definition, use the CREATE VIEW command

7. Views
When a query involves a view, SQL changes the query to select data from the table(s) in the database that created the view

8. Views The use of views provides several benefits
Views provide data independence
The display of data can be customized to meet each user’s needs
A view contains only those columns required by a given user, which has two advantages:
A view greatly simplifies the user’s perception of the database
Views provide a measure of security

9. Row-and-Column Subsets
A row-and-column subset view that contains the primary key of the underlying base table is updateable
Figure 6.9 illustrates a view that contains serious update problems due to the exclusion of the primary key

10. Row-and-Column Subsets
Figure 6.9

11. 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

12. Statistics
CRED_CUST view contains the most troublesome view of all because it involves statistics calculated from one or more base tables
Rows cannot be added to a view that includes calculations

13. Dropping a View
When a view is no longer needed, remove it by using the DROP VIEW command
Example:
DROP VIEW HSEWRES;

14. Security
Security is the prevention of unauthorized access to the database
Two security mechanisms:
Views
GRANT command

15. Security
The database administrator can grant different types of privileges to users and then revoke them later, if necessary
User privileges can be granted and revoked using the GRANT and REVOKE commands, respectively

16. Security Problem: Solution:
User Johnson must be able to retrieve data from the REP table.
Solution:
GRANT SELECT ON REP TO JOHNSON;

17. Security The privileges that can be granted are:
SELECT to retrieve date
UPDATE to change data
DELETE to delete data
INSERT to add new data
INDEX to create an index
ALTER to change the table structure

18. Security The REVOKE command is used to revoke privileges from users
Problem:
User Johnson is no longer allowed to retrieve data from the REP table.
Solution:
REVOKE SELECT ON REP FROM JOHNSON;

19. Indexes
An index can be created for any column or combination of columns in any table
After creating an index, the DBMS uses it to speed up data retrieval

20. Indexes Advantages Disadvantages
Makes certain types of retrieval more efficient
Disadvantages
Occupies disk space and is technically unnecessary
Must be updated whenever corresponding data in the database is updated

21. Creating an Index Problem:
Create an index named BALIND on the BALANCE column in the CUSTOMER table.
Create an index named REPNAME on the combination of the LAST_NAME and FIRST_NAME columns in the REP table.
Create an index named CREDNAME on the combination of the CREDIT_LIMIT and CUSTOMER_NAME columns in the CUSTOMER table, with the credit limits listed in descending order.

22. Creating an Index Solution:
CREATE INDEX BALIND ON CUSTOMER(BALANCE);   CREATE INDEX REPNAME ON REP(LAST_NAME, FIRST_NAME);   CREATE INDEX CREDNAME ON CUSTOMER(CREDIT_LIMIT DESC, CUSTOMER_NAME);

23. Dropping an Index
The command used to drop (delete) an index is DROP INDEX
Problem:
Delete the CREDNAME index
Solution:
DROP INDEX CREDNAME;

24. Unique Indexes
When a column that is not the primary key requires unique values, create a unique index
A unique index is created by using the CREATE UNIQUE INDEX command

25. Unique Indexes Problem: Solution:
Create a unique index named SSN on the SOC_SEC_NUM column of the REP table
Solution:
CREATE UNIQUE INDEX SSN ON REP(SOC_SEC_NUM);

26. System Catalog
Information about tables in the database is kept in the system catalog or the data dictionary
System catalog contains tables:
SYSTABLES (in Oracle: DBA_TABLES)
SYSCOLUMNS (in Oracle: DBA_TAB_TABLES)
SYSVIEWS (in Oracle: DBA_VIEWS)

27. System Catalog The system catalog is a relational database
Information can be retrieved by using the same types of queries which are used to retrieve data in a relational database

28. System Catalog The DBMS updates the system catalog automatically
Users should not use SQL queries to update the catalog directly because this might produce inconsistent information

29. Integrity Rules in SQL
An integrity constraint is a rule for the data in the database
If a user enters data in the database that violates any of the integrity constraints, the database will develop serious problems

30. Integrity Rules in SQL
Integrity support is the process of specifying integrity constraints for a database that the DBMS will enforce
The types of constraints supported in SQL are:
Primary keys
Foreign keys
Legal values

31. Integrity Rules in SQL
In most cases, a table’s primary key is indicated when the table is created
To add a primary key after creating a table, use the ADD PRIMARY KEY clause of the ALTER TABLE command

32. Integrity Rules in SQL
A foreign key is a column in one table whose values match the primary key in another table
When a table contains a foreign key, it is identified by using the ADD FOREIGN KEY clause of the ALTER TABLE command
After creating a foreign key, the DBMS will reject any update that violates the foreign key constraint

33. Integrity Rules in SQL
The CHECK clause of the ALTER TABLE command is used to ensure that only legal values satisfying a particular condition are allowed in a given column
If a user enters data that violates the condition, the DBMS rejects the update automatically

34. Summary
A view contains data that is derived from existing base tables when users attempt to access the view
GRANT command: gives users access privileges to data in the database
REVOKE command: terminates previously granted privileges
You can create and use an index to make data retrieval more efficient

35. Summary
The DBMS maintains information about the tables, columns, indexes, and other system elements in the system catalog (catalog) or data dictionary
Integrity constraints are rules that the data in the database must follow to ensure that only legal values are accepted in specified columns and that primary and foreign key values match between tables

36. SQL Project Six Completed
Good Luck
H. Zamanzadeh