MELJUN CORTES Advanced prog. java ou module 7

MODULE 7 database and Sql fundamentals

LESSON 7 DATABASE AND SQL FUNDAMENTALS

Leaning Objectives:

Keywords and Phrases

LEARNER

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Database Data Definition LanguageRelational Database Data Manipulation LanguageStructured Query Language

When you finish this lesson, you will be able to do the following:

Understand the relational database model.

Understand basic database queries using Structured Query Language (SQL).

Learn how to use Stored Procedures.

INTRODUCTION

In this module, you'll learn the fundamentals of database programming. You'll

learn how relational databases work and how SQL is used to update and retrieve data

from relational databases. You'll learn how databases are accessed and about the

different types of drivers that can be used. When you finish this chapter, you'll have the

background you need to begin Java database programming. Even if you are an

experienced database programmer, you should still skim over this chapter. It contains

useful introductory information on aspects of database programming with Java.

DATABASE AND SQL FUNDAMENTALS

What Is a Database?

A database is a collection of data that is organized so that it may be easily searched

and updated. The most important feature of a database is its organization, which

supports both ease of use and efficient data retrieval. Consider an office that is

organized with numbered file cabinets containing carefully labeled folders. Office

information is stored by subject in specific folders that are kept in designated file

cabinets. In such a system, every folder has its place and it is easy to find a particular

folder.

Now consider a different environment where information is stored in folders, but the

folders are stored in boxes that are placed at seemingly random locations throughout an

office building. How do you find a particular folder in such an environment? Where do

you store a folder when you're finished with it?

The well-organized environment is analogous to a database. Information that is entered

into a database is stored in specific locations within it. Because of the database's

structure and organization (assuming the database is well designed), information can be

easily retrieved. The database can be accessed remotely and is shared between many

users.

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The unorganized environment is analogous to a situation where information is stored in

files on various user's computers. In such an environment, it is very hard to locate

specific information. What file contains the information you need? Whose computer

contains that file? Where is the computer located? Where is the file located in the user's

file system?

A database server is a software program that manages databases, keeps them

organized, and provides shared access to them. Database servers manage and

organize databases at both a physical level and at a logical level. At a physical level, database servers store database information in specific locations within the particular

files, directories, and disk volumes used by the server. The server keeps track of what

information goes where so that you don't have to worry about it. The server is like a

trusty office assistant--you can turn to and say, "Get me the file on..." and the assistant

immediately retrieves the information you need and places it on your desk.

As previously mentioned, database servers also manage and organize information at a logical level. This logical level corresponds to the type of information that you store in a

database. For example, you may have a database that stores the names, companies,

email addresses, and phone numbers of your business contacts. The logical

organization of the database could consist of a Contacts table with five columns:

LastName, FirstName, Company, Email, and Phone. Specific contacts would be

identified by rows of the table, as shown in Table 7-1.

Table 7-1. A BUSINESS CONTACT TABLE.

LastName FirstName Company Email Phone

Smith Joe XYZ, Corp. [email protected] 123-456-7890

Jones Sally UVW, Corp. [email protected] 234-567-8901

Woods Al RST, Corp. [email protected] 345-678-9012

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Relational Databases

Although there are a number of different ways that databases can be logically

organized, one particular organization, called the relational model, is the predominant

method. The relational model was developed by E.F. Codd, a mathematician at IBM,

during the late 1960s. Databases that adhere to the relational model are referred to as

relational databases.

Relational databases are organized into tables that consist of rows and columns. As

shown in Table 43.1, the columns of the table identify what type of information is

contained in each row. The rows of the table contain specific records that have been

entered in the database. The first row of Table 7.1 indicates that Joe Smith works for

XYZ, Corp. and has email address [email protected] and phone number 123-456-7890.

(The table column headings are not counted as rows within the table.)

Organizing Tables

A relational database can have one table or 1,000 tables. The number of tables is only

limited by the relational database server software and the amount of available physical

storage. Some relational database servers, also referred to as relational database

management systems (RDBMs), organize tables into schemas. A schema is a way of

partitioning the tables of a database. Each table in a database belongs to exactly one

schema. In a similar fashion, schemas are organized into catalogs. Each schema

belongs to exactly one catalog, as shown in Figure 43.1. The purpose of schemas and

catalogs is to organize tables into related groups and control access to the information

contained in a database according to these groups.

Working with Keys

Access to information contained within tables is organized by keys. A key is a column or

group of columns that uniquely identifies a row of a table. Keys are used to find a

particular row within a table and to determine whether a new row is to be added to a

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table or to replace an existing row. Suppose that Table 7.1 was updated to include

everybody in the world with an email address. What columns should we use as a key?

At first glance we may choose the LastName column. However, many people have the

same last names. After further consideration, even if we chose the LastName,

FirstName, and Company columns as our key, we would still run into problems with

companies that had more than one Joe Smith working for them. The Email column

would make a good key, though. If two people in the same company have the same

name, they are still given unique email addresses, such as [email protected] and

[email protected]. (For the purpose of the example, we'll ignore the cases where

people share the same email address or a person has more than one email address.)

Using Email as our key, we can easily manage our business contacts table. When we

update the table, we can check to see if the Email column of the new row is already in

the table. In this case, we can overwrite the existing row with new information. If the

Email column of the new row is not in the table, we can add a new row to the table.

Normalizing Tables

When we design the tables of a database, how do we decide which information to put in

which tables? Is it better to use one big table or lots of little tables?

The answer to these questions was provided by Codd in his paper on the relational data

model. He described a process called normalization, which could be used to optimize

the way that data is organized into tables. The purpose of normalization is to minimize

the number of columns in database tables and promote data consistency. More tables

with fewer columns are the result of normalization. Five levels of normalization are

recognized. A database that is normalized to a particular level is said to be in normal

form for that level (that is, first normal form through fifth normal form). The purpose of

normalization is to remove redundant information from the database to simplify

database updating and maintenance.

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First normal form is the simplest and easiest to achieve. In it, duplicate columns of a

table are eliminated. For example, consider Table 43.2, which keeps track of the taxes

an individual paid in the years 1995 through 1997. The first column is the person's

social security number and is the key for the table. The second through fourth columns

represent the amount of tax the individual paid.

TABLE 7.2. INDIVIDUAL TAXES PAID TABLE.

SSN Tax95 Tax96 Tax97

123-45-6789 10,000 11,000 11,500

234-56-7890 4,500 5,000 5,250

Because the second through fourth columns contain the same type of information, the

table can be put into first normal form by organizing it as shown in Table 43.3.

TABLE 7.3. FIRST NORMAL FORM OF INDIVIDUAL TAXES PAID TABLE.

SSN Year Tax

123-45-6789 95 10,000

123-45-6789 96 11,000

123-45-6789 97 11,500

234-56-7890 95 4,500

234-56-7890 96 5,000

234-56-7890 97 5,250

Subsequent normal forms are more complicated and harder to achieve. In most cases,

achieving high levels of normalization is neither necessary nor desired. For example,

databases that are put in fifth normal form have a high degree of consistency because

redundant database columns are eliminated. However, this consistency comes at the

expense of requiring more tables. The additional number of tables increases the storage

space required by the database as a whole, and also increases the time to perform a

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database search. In general, database design is a trade-off between data consistency,

database size, and database performance.

Structured Query Language

The Structured Query Language, or SQL (pronounced "sequel"), is a language for

interacting with relational databases. It was developed by IBM during the '70s and '80s

and standardized in the late '80s. The SQL standard has been updated over the years,

and several versions currently exist. In addition, several database vendors have added

product-specific extensions and variations to the language. The JDBC requires JDBC-

compliant drivers to support the American National Standards Institute (ANSI) SQL-92

Entry Level version of the standard that was adopted in 1992.

SQL has many uses. When SQL is used to create or design a database, it is a data

definition language. When it's used to update the data contained in a database, it is a

data maintenance language. When it's used to retrieve information from a database, it is

a data query language. We'll cover each of these uses in the following subsections.

Using SQL as a Data Definition Language

You can use SQL to define a database. For example, there are SQL statements for

creating a database, creating tables and adding them to a database, updating the

design of existing tables, and removing tables from a database. However, most

database systems provide GUI tools for database definition, and these tools are far

easier to work with than SQL for designing a database. For example, Microsoft Access

97 provides wizards that guide you through the entire process of creating a database

and the tables that it contains. If you have access to a GUI-based database design tool,

use it. It will save you time in creating your database and make it much easier to

update. For those of you who do not have a GUI database design tool, I'll describe

some of the basic SQL statements.

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The CREATE DATABASE Statement

The CREATE DATABASE statement can be used to create a database:

CREATE DATABASE databaseName

Substitute the name of the table to be created for databaseName. For example, the

following statement creates a database named MyDBase:

CREATE DATABASE MyDBase

NOTE: The CREATE DATABASE statement is not supported by all SQL

implementations.

The CREATE TABLE Statement

The CREATE TABLE statement creates a table and adds it to the database:

CREATE TABLE tableName (columnDefinition, ... ,columnDefinition)

Each columnDefinition is of the form

columnName columnType

The columnName is unique to a particular column in the table. The columnType

identifies the type of data that may be contained in the table. Common data types are

char(n)--An n character text string

int--An integer value

float--A floating point value

bit--A boolean (1 or 0) value

date--A date value

time--A time value

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NOTE: The Types class of java.sql identifies the SQL data types supported by Java.

The get methods of the ResultSet interface are used to convert SQL data types into

Java data types. The set methods of the PreparedStatement interface are used to

convert Java types into SQL data types. These classes are covered in more detail in the

next chapter.

The following is an example of a CREATE TABLE statement:

CREATE TABLE Contacts (

LastName char(30),

FirstName char(20),

Company char(50),

Email char(40),

Phone char(20)

)

The preceding statement creates a Contacts table with the following columns:

LastName--A 30-character-wide text field

FirstName--A 20-character-wide text field

Company--A 50-character-wide text field

Email--A 40-character-wide text field

Phone--A 20-character-wide text field

The ALTER TABLE Statement

The ALTER TABLE statement adds a row to an existing table:

ALTER TABLE tableName ADD (columnDefinition ... columnDefinition)

The row values of the newly added columns are set to NULL. Columns are defined as

described in the previous section.

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The following is an example of the ALTER TABLE statement that adds a column named

Fax to the Contacts table:

ALTER TABLE Contacts ADD (Fax char(20))

The DROP TABLE Statement

The DROP TABLE statement deletes a table from the database:

DROP TABLE tableName

The dropped table is permanently removed from the database. The following is an

example of the DROP TABLE statement:

DROP TABLE Contacts

The preceding statement removes the Contacts table from the database.

Using SQL as a Data Maintenance Language

One of the primary uses of SQL is to update the data contained in a database. There

are SQL statements for inserting new rows into a database, deleting rows from a

database, and updating existing rows.

The INSERT Statement

The INSERT statement inserts a row into a table:

INSERT INTO tableName VALUES (`value1', ..., `valuen')

In the preceding form of the INSERT statement, value1 through valuen identify all

column values of a row. Values should be surrounded by single quotes.

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The following is an example of the preceding form of the INSERT statement:

INSERT INTO Contacts VALUES (

`Aro',

`Luwi',

`PUP',

`[email protected]',

`0921-5300182'

)

The preceding statement adds Luwi Aro to the Contacts table. All columns of Luwi's row

are filled in.

An alternative form of the INSERT statement may be used to insert a partial row into a

table. The following is an example of this alternative form of the INSERT statement:

INSERT INTO tableName (columnName1, ..., columnNamem) VALUES (`value1', ...,

`valuem')

The values of columName1 through columnNamem are set to value1 through valuem.

The value of the other columns of a row are set to NULL.

An example of this form of the INSERT statement follows:

INSERT INTO Contacts (LastName, Email) VALUES (

`Alet',`[email protected]'

)

The preceding statement adds a person with the last name of Alet and the email

address [email protected] to the Contacts table. The person's FirstName, Company,

and Phone fields are set to NULL.

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The DELETE Statement

The DELETE statement deletes a row from a table:

DELETE FROM tableName [WHERE condition]

All rows of the table that meet the condition of the WHERE clause are deleted from the

table. The WHERE clause is covered in a subsequent section of this chapter.

WARNING: If the WHERE clause is omitted, all rows of the table are deleted.

The following is an example of the DELETE statement:

DELETE FROM Contacts WHERE LastName = Àro'

The preceding statement deletes all contacts with the last name of Aro from the

Contacts table.

The UPDATE Statement

The UPDATE statement is used to update an existing row of a table:

UPDATE tableName SET columnName1 = `value1', ... ,columnNamen = `valuen'

[WHERE condition]

All the rows of the table that satisfy the condition of the WHERE clause are updated by

setting the value of the columns to the specified values. If the WHERE clause is

omitted, all rows of the table are updated.

An example of the UPDATE statement follows:

UPDATE Contacts SET FirstName = Àlet ' WHERE LastName = Àro'

The preceding statement changes the FirstName of all contacts with the LastName of

Deloach to Tim.

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Using SQL as a Data Query Language

The most important use of SQL for many users is for retrieving data contained in a

database. The SELECT statement specifies a database query:

SELECT columnList1 FROM table1, ..., tablem [WHERE condition] [ORDER BY

columnList2]

In the preceding syntax description, columnList1 and columnList2 are comma-

separated lists of column names from the tables table1 through tablem. The SELECT

statement returns a result set consisting of the specified columns of the table1 through

tablem, such that the rows of these tables meet the condition of the WHERE clause. If

the WHERE clause is omitted, all rows are returned.

NOTE: An asterisk (*) may replace columnList1 to indicate that all columns of the

table(s) are to be returned.

The ORDER BY clause is used to order the result set by the columns of columnSet2.

Each of the column names in the column list may be followed by the ASC or DESC

keywords. If DESC is specified, the result set is ordered in descending order.

Otherwise, the result set is ordered in ascending order.

An example of the SELECT statement follows:

SELECT * FROM Contacts

This statement returns all rows and columns of the Contact table.

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The WHERE Clause

The WHERE clause is a boolean expression consisting of column names, column

values, relational operators, and logical operators. For example, suppose you have

columns Department, Salary, and Bonus. You could use the following WHERE clause to

match all employees in the Engineering department that have a salary over 100,000

and a bonus less than 5,000:

WHERE Department = `Engineering' AND Salary > `100000' AND Bonus < `5000'

Relational operators are =, !=, <, >, <=, and >=. Logical operators are AND, OR, and

NOT.

NOTE: The ANSI SQL standard provides additional operators besides those listed in

this section.

Remote Database Access

Most useful databases are accessed remotely. In this way, shared access to the

database can be provided to multiple users at the same time. For example, you can

have a single database server that is used by all employees in the accounting

department.

In order to access databases remotely, users need a database client. A database client

communicates to the database server on the user's behalf. It provides the user with the

capability to update the database with new information or to retrieve information from

the database. In this book, you'll learn to write Java applications and applets that serve

as database clients. Your database clients talk to database servers using SQL

statements.

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ODBC and JDBC Drivers

Database clients use database drivers to send SQL statements to database servers and

to receive result sets and other responses from the servers. JDBC drivers are used by

Java applications and applets to communicate with database servers. Officially, Sun

says that JDBC is an acronym that does not stand for anything. However, it is

associated with "Java database connectivity."

Microsoft's ODBC

Many database servers use vendor-specific protocols. This means that a database

client has to learn a new language to talk to a different database server. However,

Microsoft established a common standard for communicating with databases, called

Open Database Connectivity (ODBC). Until ODBC, most database clients were server-

specific. ODBC drivers abstract away vendor-specific protocols, providing a common

application programming interface to database clients. By writing your database clients

to the ODBC API, you enable your programs to access more database servers.

Enter JDBC

So where does JDBC fit into this picture? It's not a competitor to ODBC yet, but it soon

will be. JDBC provides a common database-programming API for Java programs.

However, JDBC drivers do not directly communicate with as many database products

as ODBC drivers. Instead, many JDBC drivers communicate with databases using

ODBC. In fact, one of the first JDBC drivers was the JDBC-ODBC bridge driver

developed by JavaSoft and Intersolv.

Why did JavaSoft create JDBC? What was wrong with ODBC? There are a number of

reasons why JDBC was needed, which boil down to the simple fact that JDBC is a

better solution for Java applications and applets:

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ODBC is a C language API, not a Java API. Java is object-oriented and C is not.

C uses pointers and other "dangerous" programming constructs that Java does

not support. A Java version of ODBC would require a significant rewrite of the

ODBC API.

ODBC drivers must be installed on client machines. This means that applet

access to databases would be constrained by the requirement to download and

install a JDBC driver. A pure Java solution allows JDBC drivers to be

automatically downloaded and installed along with the applet. This greatly

simplifies database access for applet users.

JavaSoft created the Java-ODBC bridge driver as a temporary solution to database

connectivity until suitable JDBC drivers were developed. The JDBC-ODBC bridge driver

translates the JDBC API into the ODBC API and is used with an ODBC driver. The

JDBC-ODBC bridge driver is not an elegant solution, but it allows Java developers to

use existing ODBC drivers.

Since the release of the JDBC API, a number of JDBC drivers have been developed.

These drivers provide varying levels of capability. As a service to Java developers,

JavaSoft has classified JDBC drivers into the following driver types:

JDBC-ODBC bridge plus ODBC driver--This driver category refers to the original

JDBC-ODBC bridge driver. The JDBC-ODBC bridge driver uses Microsoft's

ODBC driver to communicate with database servers. It is implemented in both

binary code and Java and must be preinstalled on a client computer before it can

be used.

Native-API partly Java driver--This driver category consists of drivers that talk to

database servers in the server's native protocol. For example, an Oracle driver

would speak SQLNet, while a DB2 driver would use an IBM database protocol.

These drivers are implemented in a combination of binary code and Java, and

they must be installed on client machines.

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Reading Assignment:

E-books

o http://java.sun.com/docs/books/tutorial/

o http://www.java-samples.com/showtutorial.php?tutorialid=293

o http://roseindia.net/jsp/simple-jsp-example/nesting-try.shtml

Exercises/Written Assignments

1. Differentiate the following terms:

a) Database

b) Database server

c) Physical level

d) Logical Level

e) Relational Database

f) Normalization

2. Define the function of each SQL statement

a) Create

b) Alter

c) Drop

d) Insert

e) Delete

f) Update

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http://roseindia.net/jsp/simple-jsp-example/nesting-try.shtml

http://www.java-samples.com/showtutorial.php?tutorialid=293

http://java.sun.com/docs/books/tutorial/

Case Problem

Using the techniques shown in this module, define a complete query application

for the Books table with the following columns: BookID, BookTitle, Author, Publisher,

DatePublished. (Create a table using MS Access) Provide the following predefined

queries:

a. Select all authors from the Authors table.

b. Select a specific author and list all books for that author. Include the title,

publisher, and date published. Order the information alphabetically by title.

c. Add a new author.

d. Edit the existing information for an author.

e. Delete an existing author.

References/Bibliography




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