The flood of information has not diminished. People are flooded with all kinds of information, such as TV, Internet and advertisements crammed with mailboxes. Unfortunately, with the increase of information, the quality of information is declining sharply. Books were replaced by periodicals and magazines, then by newspapers, web pages and blogs, and finally by Twitter. The amount of information becomes more and more huge and unreliable. To make matters worse, the data in the Internet age will never really disappear. It accumulates and is hidden in various file logs and databases. Eric Schmidt, the former CEO of Google, said that the amount of data created by human beings in two days is equivalent to that created in 2000 (or any year) since the appearance of written records, that is, it only takes two days to create about EB (that is, 1 100 billion GB), and the pace is still accelerating.

When storing data electronically becomes a reality, it also brings its own rules. In order to understand the meaning of data, people must learn the corresponding language relational database theory, which gives people the ability to control electronic data. It uses structured query language SQL to process data, and relational database has achieved great success so far.

Since relational database was first put forward in 1990s, relational database and SQL have made great progress. Concepts contained in relational databases and SQL may not be intuitive enough for beginners. This book will help readers understand the principle behind SQL, not only its powerful functions, but also its limitations.

Reader object

This book begins with introductory knowledge, which introduces readers that they don't need to have preparatory knowledge of SQL or relational database. This book will lead readers into the discovery of SQL, and readers will personally create sample databases. It not only combines the SQL concepts introduced in this book, but also introduces the concepts of data modeling, query adjustment and optimization through repeated reconstruction. This book also introduces some best practices that apply to every SQL.

This book is suitable for computer programmers who are ready to learn relational database programming, and also for business users who want to release more capabilities from the database. SQL is the universal language in the relational database world, and anyone interested in learning this powerful language is suitable to read this book.

Readers who have some previous database experience can skip the first two chapters and jump directly to more advanced content. Of course, they can also review the important principles introduced in these two chapters.

abstract

This book introduces the published SQL standard SQL: it focuses on the practical application of SQL language and emphasizes the differences between different SQL implementations. This book introduces many examples, in which the latest version of modern database system is used to realize SQL. These databases are either free downloadable versions of Express or free open source software. In addition, this book also introduces the most popular. Popular desktop database software Microsoft Access and OpenOffice The databases introduced in this book include

IBM UDB company

Oracle Bone Inscriptions g

Microsoft SQL Server / /

MySQL /

A database system

Microsoft Access /

OpenOffice BASE with embedded HSQLDB

Page structure

This book introduces the general concepts of relational database, especially those in SQL, to readers step by step through a process of repeatedly reconstructing the database. In this process, every concept introduced at the beginning is analyzed in more detail, thus inspiring readers to understand the relevance behind these concepts.

The first chapter briefly introduces SQL and the relational theory behind it. This chapter only briefly introduces the most basic concept of database, and the following chapters are based on it. This chapter introduces the difference between data and information, and some basic principles need to be further explained in later chapters. This chapter also outlines the relational database management system (RDBMS) used in this book.

According to the analysis of the relational model, unstructured data should be structured to meet the requirements of the relational model, that is, the refrigerator magnet mode should be converted into the closet mode first, and then it should be converted into the actual table in the relational database.

This chapter further introduces the relational model, the basic design of database and the basic process of standardization. This chapter also introduces some SQL tools used to perform queries on standardized data. In addition, this chapter also introduces dynamic SQL.

SQL is a collection-based language, which makes it have both powerful functions and certain limitations. Chapter 1 discusses the most popular process extensions (such as PL/SQL of Oracle and Transact SQL of Microsoft). This chapter also introduces SQL function, which can be used as a supplementary means to make up for the inherent shortcomings of SQL in dealing with record-based logic.

Chapter 1 introduces the data collection, and summarizes the capabilities and limitations of this method. This chapter raises the SQL aggregate function introduced in the previous chapter to a new level, and demonstrates how to use SQL to obtain the aggregate value of data.

This chapter introduces subqueries. When the data sets are staggered and the query data needs to be filtered by multilevel data, one query can be used as the filtering condition of another query, and SQL statements can be adjusted to replace subqueries with JOIN, which is one of the themes throughout this book.

The powerful function of SQL lies in processing data stored in multiple relational tables. Chapter 1 introduces how SQL unifies the data of these relational tables into a dataset.

This book introduces the basic concepts of SQL and opens the door to further learning SQL. Chapter 1 is the next stop of SQL exploration journey, and introduces the problems that should be considered in further learning SQL.

The second chapter introduces the performance optimization technology, and describes the common methods and best practices of optimizing query and database environment. The second chapter discusses the working principle of relational database in multi-user environment, and introduces the mechanism of handling concurrent data access realized by SQL.

All operations of SQL are related to structure and order. After all, it is a structured query language, and the real data can be of various sizes and structures. Chapter 1 introduces how SQL handles semi-structured data (XML documents), unstructured data (text files) and binary data (such as pictures and sounds).

The first chapter briefly discusses the latest development in database field, such as column database, NoSQL database, object database and service-oriented architecture (SOA), and their relationship with SQL.

For each database discussed in this book, Appendix A describes the process of gradually installing the sample database library and how to use specific instructions to generate the initial data of the library database. These SQL scripts can be downloaded from the support website of this book.

Appendix B of the relational database software package introduced in this book provides a detailed installation process.

Appendix C describes the tools provided by each database, which can be used to access, create database objects and manipulate data stored in tables.

Appendix D introduces the general SQL client of the open source project SQuirreL, which can access various databases through the Java database connection (JDBC) interface. This appendix details how to install and configure the software.

Conditions for learning this book

In order to make full use of this book, it is recommended to download and install the relational database software used in this book. Most of these softwares are free or have free trial versions. You can install these softwares by following the steps described in Appendix B..

Support websites and codes

When studying each chapter, it is recommended to download the corresponding SQL script to create and generate the database. The code that can be downloaded to this book from wrox or agilitator can be used in the support website to find the book with the specified name. After finding the specified book, click the download code link to access the files that are allowed to download. These codes can be downloaded via HTTP or FTP. All files are saved in ZIP format.

The ISBN of this book is more convenient to find this book by ISBN number than by its title.

In addition, you can download the code of this book from the download page wrox/dynamic/books/downloadaspx. Just click on the link of DiscoveringSQL: A Practical Guide for Beginners to access the files that are allowed to be downloaded.

corrigendum

Although we have done our best to ensure that there are no mistakes in the article or code, mistakes are always inevitable. If you find mistakes in this book, such as spelling mistakes or code mistakes, please tell us. We will be very grateful that the errata can help other readers avoid going astray and of course help to provide higher quality information.

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If you don't find any errors in the errata, you can fill in the above table on wrox /contact/techsupport s and send us the errors you find. We will check the information, and if it is correct, we will put it in the errata of this book and correct these problems in subsequent editions of this book.

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