Chapter 8
Databases
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
RDBMS
• A Relational Database Management
System (RDBMS) provides data storage
and access for web applications
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, #)
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
Database Structure
• Each table field represents an entity attribute
• Each table row represents one entity
Car table:
Year
1973
1992
2004
row
field
Make
Model
Color
Volkswagen Jetta
Red
Ford
Aerostar Blue
Chevrolet
Suburban Black
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
Basic SQL Statements
• Data definition
– CREATE, DROP
• Data manipulation
– SELECT, INSERT, UPDATE, DELETE
• Data control
– GRANT, REVOKE
CREATE
• Create a database or a table
CREATE DATABASE ehsl
CREATE ehsl.player (
playerNr int PRIMARY KEY,
name VARCHAR(30),
isCurrent BOOLEAN NOT NULL)
Basic SQL Data Types
• INTEGER
• DECIMAL(T, R)
– T=total digits, R=right digits (after '.')
• FLOAT
• CHAR(N)
• VARCHAR(N)
• BOOLEAN
• DATE
• TIME
N characters
up to N characters
DROP
• DROP can be used to delete an entire
database or a table
DROP ehsl
DROP ehsl.player
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
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
INSERT
• INSERT adds a new row to a table
INSERT INTO ehsl.player
VALUES (23752, 'Jane Doe', TRUE)
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
DELETE
• DELETE removes one or more rows from
a table
DELETE FROM database.table
WHERE condition
DELETE FROM ehsl.player
WHERE playerNr=33523
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!
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 user@host, for
example 'jonesac'@'localhost'
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 'jonesac'@'localhost'
Create User
• The CREATE command can also be used
to create new users
CREATE USER user-name
IDENTIFIED BY password
CREATE USER 'jonesac'@'localhost'
IDENTIFIEC BY 'abc123#'
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
Application
Program
RDBMS
Driver
JDBC
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) {
….
}
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();
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));
}
access the next row of the table
// get field values
while (rs.next()) {
for (int i = 1; i<=md.getColumnCount(); i++) {
result.addFieldValue(rs.getString(i));
}
}
access the next field of the row
con.close();
} catch (SQLException s) {
...
}
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)
JDBC Design
• An effective design for database access:
– JSP:
– Java Servlet:
– Java Bean:
JSP
create user interface
Java Servlet
process / prepare
data
user interface presentation
application logic
database access (JDBC)
Java Bean
access RDBMS
using JDBC
RDBMS
dependency
Database Design Principles
1. Each field should contain a single value
2. Repeated fields with empty values
should be made a separate table
3. Each table should represent only one
entity
Example: Registration
• WRONG:
multiple valued field
• Better:
empty fields
Example: Registration
• Better still:
multiple entities:
class registration /
class name
Example: Registration
• RIGHT:
Review
• Relational Database / RDBMS
• SQL
– Data Definition
– Data Manipulation
– Data Control
• JDBC
– Database Driver
– Query Execution
– Command Execution
• Database Design Principles