The Language of SQL- P4 pptx

I’ll also talk about the features of this book, which will allow you to determine readily the SQL syntax for the specific database you’re using.. In common usage, the databases in these

Databases and SQL

In this first chapter, I’m going to provide a bit of background that will allow you to get started quickly with the writing of SQL statements in subsequent chapters There are two general topics The first will be an overview of the data-bases covered in this book and some basic information on how those datadata-bases relate to the language of SQL I’ll also talk about the features of this book, which will allow you to determine readily the SQL syntax for the specific database you’re using

Second, I’m going to cover some of the key design features of relational data-bases We’ll talk about tables, rows, columns, keys, and datatypes After you have the basic information, you’ll be up and running in no time So, without further ado, let us begin

Language and Logic

I must begin with an admission that the title of this book is not entirely

appro-priate Although the book is entitled The Language of SQL, a more apt title might have been The Logic of SQL This is because, like all computer languages, the

language of SQL has much more to do with cold, hard logic than with English vocabulary

Nevertheless, there is a unique language-based syntax present in SQL that dis-tinguishes it from many other computer languages Unlike many programming tools, SQL employs ordinary English words such asWHERE, FROM, and HAVING

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as keywords in its syntax As a result, SQL is much less cryptic than other languages you might have seen

As such, after you become familiar with the language of SQL, you might find yourself thinking of SQL commands as being analogous to English sentences and having a certain expressive meaning

For example, compare this sentence:

I would like a hamburger and fries from your value menu,

and make it to go.

with this SQL statement:

Select city, state

from customers

order by state

I’ll get into the details later, but this SQL statement means that you want the city and state fields from a customer’s table in your database, and you want the results sorted by state

In both cases, you’re specifying which items you want (hamburger/fries or city/ state), where you want it from (value menu or customer’s table), and some extra instructions (make it to go or sort the results by state)

So an important goal of this book is to allow you to learn SQL as you would learn English, in a simple, intuitive way My approach will be to introduce one word at

a time, while building on the logical intent and meaning of the language

There is a second and perhaps less obvious meaning to the title of this book There

is often some confusion between the language of SQL and SQL databases There

are many software companies selling database management systems (DBMS) software In common usage, the databases in these types of software packages are

often referred to as SQL databases, since the SQL language is the primary means

of managing and accessing data in these databases Some vendors even use the

word SQL as part of the database name For example, Microsoft calls its latest DBMS SQL Server 2008.

But, in point of fact, SQL is more properly a language It is not really a database

My focus in this book will be on the language of SQL rather than on any parti-cular database

Chapter 1 ■ Relational Databases and SQL

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SQL Defined

So what is SQL? In a nutshell, SQL is a standard computer language for

main-taining and utilizing data in relational databases Put simply, SQL is a language

that lets users interact with relational databases It has a long history of

devel-opment by various organizations going back to the 1970s In 1986, the American

National Standards Institute (ANSI) published its first set of standards regarding

the language, and it has gone through several revisions since that time

Generally speaking, there are three major components of the SQL language The

first is called DML, or Data Manipulation Language This module of the language

allows you to retrieve, update, add, or delete data in a database The second

component is called DDL, or Data Definition Language DDL enables you to

create and modify the database itself For example, DDL providesALTER

state-ments, which let you modify the design of tables in a database Finally, the third

component, DCL, or Data Control Language, maintains proper security for the

database

Many of the major software vendors, such as Microsoft and Oracle, have adapted

the standard for their own purposes and have added numerous extensions and

modifications to the language But although each vendor has its own unique

interpretation of SQL, there is still an underlying base language, which is pretty

much the same for all vendors That is what we will be covering in this book

As a computer language, SQL is different than other languages you may be

familiar with, such as Visual Basic or C++ Other languages tend to be procedural

in nature That means that they allow you to specify particular procedures to

accomplish a desired task SQL is more of a declarative language In SQL, the

desired objective is often declared with a single statement The simpler structure

of SQL is possible since it is only concerned with relational databases rather than

the entirety of computer systems

Microsoft SQL Server, Oracle, and MySQL

Although my aim is to cover the core language of SQL as it applies to all

implementations, I will also provide specific examples of SQL syntax And since

syntax does vary somewhat among vendors, I’ve decided to focus on the SQL

syntax utilized by these three databases:

■ Microsoft SQL Server

■ Oracle Database

■ MySQL

If there are any differences among these three databases, I’ll present the syntax for Microsoft SQL Server in the text of the book I’ll then indicate any differences for MySQL or Oracle in a box such as the following:

D A T A B A S E D I F F E R E N C E S

A box such as this one will appear whenever I present syntax differences for Oracle Database or MySQL The syntax for Microsoft SQL Server will appear in the main text.

The heading of the box will indicate if the note is for MySQL, Oracle, or both.

Microsoft SQL Server is available in several versions and editions The most recent

version is called Microsoft SQL Server 2008 Available editions run from a basic

Express edition to a fully featured Enterprise edition The Express edition is free but still has an abundance of features that allow you to get started with full-fledged database development The Enterprise edition includes many sophisticated data-base management features, plus sophisticated business intelligence components Oracle is also available in a number of editions The most recent version is called

Oracle Database 11g Like Microsoft, Oracle also offers a free Express edition of

its database

MySQL is an open source database, which means that no one single organization owns or controls its development Although MySQL was purchased by Sun Microsystems in 2008, it remains one of the top choices for open source software Sun Microsystems was later purchased by Oracle As an open source database, MySQL is available on numerous platforms other than Windows, such as Mac OS X and Linux MySQL offers its Community Edition as a free download

When starting out, it is sometimes useful to download the database of your choice, so you have something to experiment with However, this book does not require you to do that This book has been written in such a way as to allow you

to learn SQL simply by reading through the text I’ll provide enough data in the text that you can understand the results of various SQL statements without having to download software and type in statements yourself

Nevertheless, if you would like to download the free versions of any of these databases, the first three appendices at the back of this book have some useful

Chapter 1 ■ Relational Databases and SQL

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instructions and tips on how to do that Appendix A has complete information

on how to get started with Microsoft SQL Server The instructions include details

on how to install the software and execute SQL commands Similarly, Appendix

B covers MySQL, and Appendix C explains Oracle

In addition, Appendix D points to supplemental material that lists all the SQL

statements shown in this book in all three databases As mentioned, we show all

SQL statements in this book in the syntax of Microsoft SQL Server In most

cases, these statements also work in MySQL and Oracle, but there are occasional

differences

Most readers will find it completely unnecessary to download the software or view

the additional material shown in Appendix D The examples shown throughout

this book are self-explanatory and don’t require you to do anything else in order to

understand the material However, if you are so inclined, then feel free to take

advantage of these extra features

Other Databases

In addition to Microsoft SQL Server, Oracle, and MySQL, there are many other

SQL database software implementations Some of the more popular packages are

the following:

■ Microsoft Access from Microsoft

■ DB2 from IBM

■ Informix from IBM

■ SQL Anywhere from Sybase

■ PostgreSQL, which is an open source database

Of these listed databases, Microsoft Access is somewhat unique, and it’s

parti-cularly useful for SQL novices who want to learn the language In essence, Access

is a graphical interface for relational databases In other words, Access allows you

to create a query against a relational database entirely through graphical means

The useful aspect of Access for beginners is that you can easily create a query in a

visual way and then switch to a SQL view to see the SQL statement you just

created So you can try different things and quickly see what the corresponding

SQL syntax looks like