Chapter 8Databases

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 domainsEx: 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

Book

Loan(transaction)

Recording

Database Structure

• Each table field represents an entity attribute• Each table row represents one entity

Year Make Model Color

1973 Volkswagen Jetta Red

1992 Ford Aerostar Blue

2004 Chevrolet Suburban Black

Car table:

field

row

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) N characters• VARCHAR(N) up to N characters

• BOOLEAN

• DATE• TIME

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.tableSET field-assignment-listWHERE condition

UPDATE ehsl.player

SET isCurrent=TRUEWHERE playerNr=33256

DELETE

• DELETE removes one or more rows from a table

DELETE FROM database.tableWHERE condition

DELETE FROM ehsl.playerWHERE playerNr=33523

Warning

• UPDATE and DELETE without a WHERE clause will affect all rows!

UPDATE ehsl.playerSET 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.tableTO 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.tableFROM user-name

REVOKE ALL PRIVILEGES on ehsl.playerFROM 'jonesac'@'localhost'

Create User

• The CREATE command can also be used to create new users

CREATE USER user-nameIDENTIFIED 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

RDBMS

Driver

JDBC

ApplicationProgram

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 namesfor (int i = 1; i <= md.getColumnCount(); i++) { colNames.addColumnName(md.getColumnName(i));}// get field valueswhile (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

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: user interface presentation– Java Servlet: application logic– Java Bean: database access

(JDBC)

JSPcreate user interface

Java Servletprocess / prepare

data

Java Beanaccess 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:

• Better:

multiple valued field

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