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Chapter 4
The Relational Model 3:
Advanced Topics
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Objectives

Define, describe, and use views

Use indexes to improve database
performance

Discuss entity, referential, and legal-values
integrity

Make changes to the structure of a
relational database
 Define
and use the system catalog
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Views
 Application
program’s or individual user’s
picture of the database
 Less involved than full database
 Offers simplification
 Provides measure of security

Sensitive tables or columns omitted where not
appropriate
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SQL to Create View
Figure 4.1
4
CREATE VIEW Housewares AS
SELECT PartNum, Description, OnHand, Price
FROM Part
WHERE Class=‘HW’
;
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Housewares View of Database
Figure 4.2
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Query on a View
 Selects
data only from Tables created in the
view
 Query is merged with query used to create
view
SELECT *
FROM Housewares
Actually executes as
WHERE OnHand< 25
;
SELECT PartNum, Description, OnHand, Price
FROM Part
WHERE Class=‘HW’
AND OnHand< 25
;
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Access Query Design of View
Figures 4.3 - 4.4
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Access Query Design of View with
Changed Field Names
Figures 4.5 - 4.6
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SalesCust View SQL Statement
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CREATE VIEW
SalesCust (Snum, SLast, SFirst, Cnum, CName) AS
SELECT Rep.RepNum, LastName, FirstName,
CustomerNum, CustomerName
FROM Rep, Customer
WHERE Rep.RepNum=Customer.RepNum
;
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SalesCust View
Figure 4.7
Concepts of Database Management, 4th Edition, Pratt & Adamski
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Access Query Design
of SalesCust View
Figure 4.8
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Access Query Design
of SalesCust View (con’t.)
Figure 4.9
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Advantages of Views
 Provides
data independence
 Same data viewed by different users in
different ways
 Contains only information required by a
given user
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Indexes
 Conceptually
similar to book index
 Increases data retrieval efficiency
 Automatically assigns record numbers
 Used by DBMS, not by users
 Fields on which index built called Index Key
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Customer Table with Record Numbers
Figure 4.10
Concepts of Database Management, 4th Edition, Pratt & Adamski
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Customer Table Index on
CustomerNum
Figure 4.11
Concepts of Database Management, 4th Edition, Pratt & Adamski
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Table Indexes on
CreditLimit, RepNum
Figure 4.12
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Pros/Cons of Indexes
 Can
be added or dropped without loss of
function
 Can make retrieval more efficient
 Occupies space that might be required for
other functions
 DBMS must update index whenever
corresponding data are updated
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SQL to Create Index
CREATE INDEX CustomerName
ON Customer (CustomerName)
;
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SQL to Delete Index
DROP INDEX RepBal
;
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Index on Single Field in Access
Figure 4.13
Concepts of Database Management, 4th Edition, Pratt & Adamski
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Index on Multiple Fields in Access
Figure 4.14
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Security
Prevention of unauthorized access to
database
 Two SQL security mechanisms



GRANT provides privileges to users
REVOKE removes privileges from users
GRANT SELECT ON Customer TO JONES
;
REVOKE SELECT ON Customer FROM JONES
;
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Integrity Rules
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 Related
to foreign keys and primary keys
 Defined by Dr. E.F. Codd
 Entity integrity

No field that is part of the primary key may accept
null values
 Referential

integrity
If Table A contains a foreign key matching the
primary key of Table B, then values must match
for some row in Table B or be null
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Primary Key in Access
Figure 4.15
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PRIMARY KEY (CustomerNum)
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Multi-Field Primary Key in Access
Figure 4.16
4
PRIMARY KEY (OrderNum, PartNum)
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Relationships Window to
Relate Tables in Access
Figure 4.17
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FOREIGN KEY (RepNum) REFERENCES Rep
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Specifying Referential Integrity
Figure 4.18
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Violating Referential
Integrity on Adding
Figure 4.19
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Violating Referential
Integrity on Deleting
Figure 4.20
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Legal-Values Integrity
States no record can exist with field
values other than legal ones
 Use SQL CHECK clause

CHECK (CreditLimit IN (5000, 7500, 10000, 15000)) ;
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Other SQL
Adding new field
ALTER TABLE Customer
ADD CustType CHAR(1)
;
Changing field properties
ALTER TABLE Customer
CHANGE COLUMN CustomerName TO CHAR(50)
;
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Add Field in Access
Figure 4.22
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Change Field
Characteristic in Access
Figure 4.23
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Other SQL
Deleting field
ALTER TABLE Part
DELETE Warehouse
;
Delete SQL Table
DROP TABLE SmallCust
;
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Delete Field in Access
Figure 4.24
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Delete Table in Access
Figure 4.25
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System Catalog
Information about database kept in
system catalog
 Maintained by DBMS
 Example catalog has two tables



Systables
Syscolumns
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Systables Table
Figure 4.26
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Partial Syscolumns Table
Figure 4.27
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