1. Chapter 8 Databases

2. Objectives Explain the structure of a relational database
Use SQL for creating, maintaining, and accessing relational databases
Use Java/JDBC for accessing relational databases
Explain and apply basic principles of good database design

3. RDBMS
A Relational Database Management System (RDBMS) provides data storage and access for web applications

4. Relation
relation is a mathematical term that refers to an ordered set of values drawn from different domains
Ex: a relation on numbers x letters x symbols
(55, A, #)

5. Database Structure A database includes one or more tables
Each table represents one type of entity
Example: Tables in a Library Database
Patron
Loan
(transaction)
Recording
Book

6. Database Structure Each table field represents an entity attribute
Each table row represents one entity
Car table:
Year
Make
Model
Color
1973
Volkswagen
Jetta
Red
1992
Ford
Aerostar
Blue
2004
Chevrolet
Suburban
Black
row
field

7. Structured Query Language
SQL is a standard language for creating and maintaining relational databases
SQL statement types:
data definition: create databases and tables
data manipulation: add, modify, delete data
data control: set access permissions

8. Basic SQL Statements Data definition Data manipulation Data control
CREATE, DROP
Data manipulation
SELECT, INSERT, UPDATE, DELETE
Data control
GRANT, REVOKE

9. CREATE Create a database or a table CREATE DATABASE ehsl
CREATE ehsl.player ( playerNr int PRIMARY KEY, name VARCHAR(30), isCurrent BOOLEAN NOT NULL)

10. Basic SQL Data Types INTEGER DECIMAL(T, R) FLOAT CHAR(N) N characters
T=total digits, R=right digits (after '.')
FLOAT
CHAR(N) N characters
VARCHAR(N) up to N characters
BOOLEAN
DATE
TIME

11. DROP DROP can be used to delete an entire database or a table
DROP ehsl
DROP ehsl.player

12. SELECT SELECT retrieves data from a database
SELECT field-list FROM database.table
WHERE condition
ORDER BY field-list
field-list is a comma-separated list of fields from the named table (* means "all fields")
condition is a Boolean condition using field names and/or constants

13. SELECT Example SELECT * FROM ehsl.player
SELECT playerNr, name FROM ehsl.player
WHERE isCurrent=TRUE
SELECT playerNr, name, status FROM ehsl.player
WHERE playerNr >= 90001
ORDER BY status, name

14. INSERT INSERT adds a new row to a table
INSERT INTO ehsl.player VALUES (23752, 'Jane Doe', TRUE)

15. UPDATE UPDATE changes one or more rows
UPDATE database.table SET field-assignment-list WHERE condition
UPDATE ehsl.player
SET isCurrent=TRUE WHERE playerNr=33256

16. DELETE DELETE removes one or more rows from a table
DELETE FROM database.table WHERE condition
DELETE FROM ehsl.player WHERE playerNr=33523

17. Warning UPDATE and DELETE without a WHERE clause will affect all rows!
UPDATE ehsl.player SET isCurrent=true
DELETE FROM ehsl.player
Change all rows!
Delete all rows!

18. GRANT GRANT can be used to give access permissions to users
GRANT ALL PRIVILEGES ON database.table TO user-name
user-name is formatted as for example

19. REVOKE REVOKE can be used to eliminate access permissions
REVOKE ALL PRIVILEGES on database.table FROM user-name
REVOKE ALL PRIVILEGES on ehsl.player FROM

20. Create User The CREATE command can also be used to create new users
CREATE USER user-name IDENTIFIED BY password
CREATE USER IDENTIFIEC BY 'abc123#'

21. JDBC
Java Database Connectivity (JDBC) is a Java API that allows Java programs to interact with relational database management systems
Interaction also requires a database driver, which translates JDBC commands to procedure calls on the RDBMS
RDBMS
Application
Program
Driver
JDBC

22. JDBC – Load Driver The first step is to load the database driver
Usually provided by the RDBMS vendor
String driverClassName = "com.mysql.jdbc.Driver";
try {
Class.forName(driverClassName); }
catch (ClassNotFoundException cnfe) { ….

23. JDBC – Execute Query (1/2)
To execute an SQL Query:
String query = "...";
Vector<String> colNames = new Vector<String>,
result = new Vector<String>;
try {
Connection con = DriverManager.getConnection(
dbUrl, dbUserId, dbPassword);
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query);
ResultSetMetaData md = rs.getMetaData();

24. JDBC – Execute Query (2/2)
To execute an SQL Query:
// get column names
for (int i = 1; i <= md.getColumnCount(); i++) {
colNames.addColumnName(md.getColumnName(i)); }
// get field values
while (rs.next()) {
for (int i = 1; i<=md.getColumnCount(); i++) {
result.addFieldValue(rs.getString(i));
con.close();
} catch (SQLException s) {
...
access the next row of the table
access the next field of the row

25. JDBC – Execute Command To execute an SQL command: int result = 0;
String command = "...";
try {
con = DriverManager.getConnection(
dbUrl, dbUserId, dbPassword);
stmt = con.createStatement();
result = stmt.executeUpdate(command);
con.close();
} catch (SQLException s) {
... }
result = number of rows affected
(inserted, modified, or deleted)

26. JDBC Design An effective design for database access:
JSP: user interface presentation
Java Servlet: application logic
Java Bean: database access (JDBC)
Java Bean
access RDBMS
using JDBC
JSP
create user interface
dependency
RDBMS
Java Servlet
process / prepare
data

27. Database Design Principles
Each field should contain a single value
Repeated fields with empty values should be made a separate table
Each table should represent only one entity

28. Example: Registration
multiple valued field
WRONG:
Better:
empty fields

29. Example: Registration
Better still:
multiple entities:
class registration /
class name

30. Example: Registration
RIGHT:

31. Review Relational Database / RDBMS SQL JDBC Database Design Principles
Data Definition
Data Manipulation
Data Control
JDBC
Database Driver
Query Execution
Command Execution
Database Design Principles