1 Chapter 6 Database Administration

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

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 Views A view is defined by creating a defining query (SQL command that indicates the rows and columns that will appear in the view)

5 Creating the HOUSEWARES View

6 HOUSEWARES View

7 Views Data does not exist in the form of the view Query acts as a “window” into the database (see Figure 6.3) As far as the user is concerned the entire database consists of the dark shaded portion of the PART table

8 Using the HOUSEWARES View

9 In Figure 6.4, the query first is merged with the query that defines the view, producing the following statement: SELECT PART_NUMBER, PART_DESCRIPTION, UNITS_ON_HAND, UNIT_PRICE FROM PART WHERE ITEM_CLASS = ‘HW’ AND UNITS_ON_HAND > 100;

10 CREATE VIEW Format The formulation of the view definition is: CREATE AS The defining query can be any valid SQL query

11 Renaming Columns When Creating a View

12 HOUSEWARES VIEW The HOUSEWARES view is an example of row-and-column subset view because it consists of a subset of the rows and columns in some base table

13 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

14 Row-and-Column Subsets and Updates through a View 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

15 Creating the SALES_CRED View

16 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

17 SLSREP_DEMO and SLSREP_FIN tables

18 Creating the SLSREP View

19 Using the SLSREP View

20 Statistics Views involving statistics calculated from one or more base tables won’t allow updates Rows cannot be added to a view that includes calculations

21 Dropping a View

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

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

24 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

25 Example 6 User Jones must be able to retrieve data from the SALES_REP table GRANT SELECT ON SALES_REP TO JONES;

26 Example 7 Users Smith and Brown must be able to add new parts to the PART table. GRANT INSERT ON PART TO SMITH, BROWN;

27 Example 8 User Anderson must be able to change the last name, first name, and street address of customers GRANT UPDATE ON CUSTOMER (LAST, FIRST, STREET) TO ANDERSON;

28 Example 9 User Martin must be able to delete order lines GRANT DELETE ON ORDER_LINE TO MARTIN;

29 Example 10 Every user must be able to retrieve part numbers, part descriptions, and item classes GRANT SELECT ON PART (PART_NUMBER, PART_DESCRIPTION, ITEM_CLASS) TO PUBLIC;

30 Example 11 User Roberts must be able to create an index on the SALES_REP table GRANT INDEX ON SALES_REP TO ROBERTS;

31 Example 12 User Thomas must be able to change the structure of the CUSTOMER table GRANT ALTER ON CUSTOMER TO THOMAS;

32 Example 13 User Wilson must have all privileges for the SALES_REP, CUSTOMER, and ORDERS tables GRANT ALL ON SALES_REP, CUSTOMER, ORDERS TO WILSON;

33 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

34 GRANT and REVOKE Format GRANT TO REVOKE FROM WITH GRANT OPTION is not meaningful part of REVOKE command Revoke cascades so privileges granted with the WITH GRANT OPTION are revoked for all who were granted privileges

35 Example 14 User Jones is no longer allowed to retrieve data from the SALES_REP table REVOKE SELECT ON SALES_REP FROM JONES;

36 Indexes Create and use an index to speed the searching process

37 CUSTOMER Table With Row Numbers

38 Index for CUSTOMER Table on CUSTOMER_NUMBER Column

39 Indexes Advantages 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

40 Creating Indexes

41 Dropping an Index Command to delete an index is DROP INDEX DROP INDEX CREDNAME;

42 Unique Indexes When a column that is not the primary key requires unique values, create a unique index using the CREATE UNIQUE INDEX command CREATE UNIQUE INDEX SSN ON CUSTOMER (SOC_SEC_NUMBER);

43 The System Catalog Information concerning tables known to the DBMS 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)

44 System Catalog System catalog is a relational database Users need special privileges to view the data in the system catalog

45 Tables Owned by PRATT

46 Views Owned by PRATT

47 Columns in the Customer Table

48 Integrity in SQL An integrity constraint is a rule that the data in the database must follow Examples: No two sales reps can have the same sales rep number The sales rep number for a customer must match the number of a sales rep currently in the database Item classes for parts must be AP, HW, or SG

49 Integrity Support To prevent violations, the DBMS provides integrity support Types of constraints supported in SQL Legal values Primary keys Foreign keys CHECK clause ensures that only legal values that satisfy a particular condition are allowed in a given column

50 CHECK Clause To ensure the only legal values for item class are AP, HW, or SG CHECK (ITEM_CLASS IN (‘AP’, ‘HW’, ‘SG’)) OR CHECK (ITEM_CLASS = ‘AP’ OR ITEM_CLASS = ‘HW’ OR ITEM_CLASS = ‘SG’)

51 ADD PRIMARY KEY Clause To indicate that SLSREP_NUMBER is the primary key for the SALES_REP table PRIMARY KEY (SLSREP_NUMBER)

52 Foreign Key A foreign key is a column on one table whose values match the primary key of another table To specify a foreign key, specify both the column that is a foreign key and the table it matches ADD FOREIGN KEY (SLSREP_NUMBER) REFERENCES SALES_REP

53 Assigning a Primary Key

54 Adding Foreign Keys

55 Violating Foreign Key Constraints

56 Parent and Child Figure 6.24 includes the words “parent” and “child” When a foreign key is used, the table containing the foreign key is the child and the tabled referenced by the foreign key is the parent

57 Adding Additional Integrity Constraints

58 Violating an Integrity Constraint