The Language of SQL- P4 pptx

chapter 1 Relational 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 databases 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 as WHERE, FROM, and HAVING 1 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 SQL2 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 provides ALTER 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 Microsoft SQL Server, Oracle, and MySQL 3 ■ 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: DATABASE DIFFERENCES 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 editio ns. 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 on e single organ ization owns or controls its development. Although MySQL was purchased by Sun Microsystems in 2008, it remains on e of the top choi ces f or open source software. Sun Microsystems was later purchased by Oracle. As an open source database, MySQL is available on numerous platforms other than Win dows, such as Mac OS X and Linux. MySQL offers its Community Edition as a free download. When starting out, it is sometimes useful to downloa d 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 SQL4 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. Other Databases 5 . 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. 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. 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