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Welcome to the world of relational databases and SQL! This book is written for those self-motivated individuals out there who would like to get an edge on relational database technology by learning the Structured Query LanguageSQL. This book was written primarily for those with very little or no experience with relational database management systems using SQL. This book also applies to those who have some experience with relational databases but need to learn how to navigate within the database, issue queries against the database, build database structures, manipulate data in the database, and more. This book is not geared toward individuals with significant relational database experience who have been using SQL on a regular basis.
What This Book Intends to Accomplish
This book was written for individuals with little or no experience using SQL or those who have used a relational database, but their tasks have been very limited within the realm of SQL. Keeping this thought in mind, it should be noted up front that this book is strictly a learning mechanism, and one in which we present the material from ground zero and provide examples and exercises with which to begin to apply the material covered. This book is not a complete SQL reference and should not be relied on as a sole reference of SQL. However, this book combined with a complete SQL command reference could serve as a complete solution source to all of your SQL needs.
What We Added to This Edition
This edition contains the same content and format as the first through third editions. We have been through the entire book, searching for the little things that could be improved to produce a better edition. We have also added concepts and commands from the new SQL standard, SQL:2003, to bring this book up to date, making it more complete and applicable to today's SQL user. The most important addition was the use of MySQL for hands-on exercises. By using an open source database such as MySQL, all readers have equal opportunity for participation in hands-on exercises.
What You Need
You might be wondering, what do I need to make this book work for me? Theoretically, you should be able to pick up this book, study the material for the current hour, study the examples, and either write out the exercises or run them on a relational database server. However, it would be to your benefit to have access to a relational database system to which to apply the material in each lesson. The relational database to which you have access is not a major factor because SQL is the standard language for all relational databases. Some database systems that you can use include Oracle, Sybase, Informix, Microsoft SQL Server, Microsoft Access, MySQL, and dBase.
Conventions Used in This Book
For the most part, we have tried to keep conventions in this book as simple as possible.
Many new terms are printed in italics.
In the listings, all code that you type in (input) appears in boldface monospace. Output appears in standard monospace. Any code that is serving as a placeholder appears in italic monospace.
SQL code and keywords have been placed in uppercase for your convenience and general consistency. For example:
• FROM PRODUCTS_TBL;PROD_ID PROD_DESC COST 11235 WITCHES COSTUME 29.99222 LASTIC PUMPKIN 18 INCH 7.7513 FALSE PARAFFIN TEETH 1.190 LIGHTED LANTERNS 14.515 ASSORTED COSTUMES 109 CANDY CORN 1.356 PUMPKIN CANDY 1.4587 PLASTIC SPIDERS 1.05119 ASSORTED MASKS 4.959 rows selected.
The following special design features enhance the text:
There are syntax boxes to draw your attention to the syntax of the commands discussed during each hour.
• DISTINCT COLUMN1, COLUMN2 FROM TABLE , TABLE2 ;
Note - Notes are provided to expand on the material covered in each hour of the book.
Caution - Cautions are provided to warn the reader about "disasters" that could occur and certain precautions that should be taken.
Tip - Tips are also given to supplement the material covered during appropriate hours of study.
ANSI SQL and Vendor Implementations
One thing that is difficult about writing a book like this on standard SQL is that although there is an ANSI standard for SQL, each database vendor has its own implementation of SQL. With each implementation come variations from the actual standard, enhancements to the standard, and even missing elements from the standard.
The expected question is, "Because there is an ANSI standard for SQL, what is so difficult about teaching standard SQL?" The answer to this question begins with the statement that ANSI SQL is just that: a standard. ANSI SQL is not an actual language. To teach you SQL, we had to come up with examples and exercises that involve using one or more implementations of SQL. Because each vendor has its own implementation with its own specifications for the language of SQL, these variations, if not handled properly in this book, could actually cause confusion concerning the syntax of various SQL commands. Therefore, we have tried to stay as close to the ANSI standard as possible, foremost discussing the ANSI standard and then showing examples from different implementations that are very close, if not the same, as the exact syntax that ANSI prescribes.
We have, however, accompanied examples of variations among implementations with notes for reminders and tips on what to watch out for. Just remember this: Each implementation differs slightly from other implementations. The most important thing is that you understand the underlying concepts of SQL and its commands. Although slight variations do exist, SQL is basically the same across the board and is very portable from database to database, regardless of the particular implementation.
Understanding the Examples and Exercises
We have chosen to use MySQL for most of the examples in this book due to its high compliance to the ANSI standard; however, we have also shown examples from Oracle, Sybase, Microsoft SQL Server, and dBase.
The use of MySQL for hands-on exercises was chosen so that all readers may participate, with minimal confusion in converting SQL syntax into the proper syntax of the database each reader is using. MySQL was chosen for exercises because it is an open source database (free), it is easy to install, and its syntax is very similar to that of the ANSI Standard. Additionally, MySQL is compatible with most operating system platforms.
In Appendix B, "Using MySQL for Exercises," we show you how to obtain and install MySQL. After it is installed on your computer, MySQL can be used for most of the exercises in this book. Unfortunately, because MySQL is not fully ANSI SQL compliant, MySQL exercises are not available for every subject.
As stated, some differences in the exact syntax exist among implementations of SQL. For example, if you attempt to execute some examples in this book, you might have to make minor modifications to fit the exact syntax of the implementation that you are using. We have tried to keep all the examples compliant with the standard; however, we have intentionally shown you some examples that are not exactly compliant. The basic structure for all the commands is the same. To learn SQL, you have to start with an implementation using practical examples. For hands-on practice, we use MySQL. If you have access to another database implementation such as Oracle, we encourage its use for hands-on exercises. You should be able to emulate the database and examples used in this book without much difficulty. Any adjustments that you might have to make to the examples in this book to fit your implementation exactly will only help you to better understand the syntax and features of your implementation.
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