快速掌握SQL：从入门到实践指南

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《SQL语言的艺术：第二版》(The Language of SQL, Second Edition)由Larry Rockoff撰写，是一本专为SQL初学者设计的实用指南。它在众多SQL入门书籍中独树一帜，其核心目标是帮助读者理解SQL的基本概念，通过清晰的解释和实例掌握SQL语句的功能，而非仅仅提供冗余的语法参考。本书的最大特点在于无需读者下载软件或实际操作计算机，而是通过阅读文本就能理解SQL的用法示例，方便学习者在没有实际环境的情况下进行理论学习。组织结构逻辑性强，SQL关键字按顺序逐个介绍，确保读者在接触新术语和概念时逐步建立扎实的基础。本书覆盖了三个主流数据库系统：Microsoft SQL Server、MySQL和Oracle。每个章节中都包含“数据库差异”侧栏，明确了这三个系统之间可能存在的语法差异，并指导如何获取和安装免费版本的数据库，以便实践所学知识。《SQL语言的艺术：第二版》共分为20章，涵盖了关系数据库和SQL基础、数据检索、计算字段和别名、函数应用、数据排序、选择标准、布尔逻辑、条件逻辑、数据汇总、子查询等核心主题，还包括更高级的主题如自连接、视图、存储过程、数据修改以及数据库设计原则等。附录部分则提供了各数据库的入门教程，包括Microsoft SQL Server、MySQL和Oracle的安装指南。作为一本全面且易于理解的SQL教材，本书旨在帮助读者快速掌握SQL语言，了解如何从关系数据库中提取数据，运用函数和计算，对数据进行各种形式的分析，以及利用复杂的逻辑规则来筛选所需信息。此外，它还教授如何更新数据、创建新表、设计直观易用的数据库结构，以及如何利用电子表格转换数据以呈现有意义的展示。《SQL语言的艺术：第二版》是一本理想的起点书籍，无论你是数据库新手还是希望提升SQL技能的专业人士，都能从中获益匪浅。它不仅包含了丰富的实用技巧，而且还注重引导读者理解和应用这些技术，从而在实际工作中发挥出SQL的强大功能。

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Introduction

• Coverage of subtotals and crosstabs

We added a new chapter on subtotals and crosstabs to provide additional possibilities for

summarizing data. This material allows users to add subtotals and running totals to their

queries. Additionally, exposure to SQL crosstab queries allows for a greater appreciation

of the value of pivot tables, which are covered toward the end of the book.

• Coverage of ranking functions

We added new material on ranking functions. This important class of functions permits

users to produce row numbers and calculate percentiles. A related capability is the ability

to divide data into partitions prior to the application of ranking functions.

• Expanded coverage of conditional logic

Our first edition included some basic material on the CASE expression and conditional

logic. This topic is often excluded from introductory SQL books but nevertheless has

tremendous practical value for any SQL developer. This second edition adds a number of

new examples in Chapters 8 and 9 of how the CASE expression can be employed.

• New and more consistent datasets

As in the first edition, each chapter has its own small set of data for examples. However,

unlike before, this second edition now uses a consistent set of datasets for all chapters. A

Customers table referenced in one chapter will be the same as a Customers table in any

other chapter. If you wish to load sample data for testing, you can now run a single script

to load all data at once. The previous edition required separate scripts for each chapter.

• Other improvements

A few other noteworthy topics have been added, including common table expressions and

comments. Terminology throughout the book has been modified for greater consistency

and conformity with standard usage. Finally, an overview of the SELECT statement has

been added early in Chapter 2, to give you a better idea of the topics to come.

Plan of the Book

This book presents its topics in a unique sequence. The majority of SQL books run through

their topics as if you were a database administrator who needs to create and design a database

from scratch, then load the database with data, and then finally start to retrieve that data. In

this book, we start right off with data retrieval, and then come around to database design in the

final chapters. This is done as a motivational tactic, allowing you to quickly get into interesting

topics related to data retrieval before having to deal with the more arcane subjects of indexes

and foreign keys.

The 20 chapters in the book can be broken down into a number of broad sections:

• Chapter 1 presents introductory material about relational databases that is necessary to

understand before encountering the SELECT statement.

• Chapters 2 through 5 begin an exploration of the SELECT statement, covering the basics

of calculations, functions, and sorting.

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Chapter 1Relational Databases andSQL

We’ll get into the details later, but this SQL statement means that we want the city and state

fields from a table named Customers in a database, and we want the results sorted by state.

In both cases, we’re specifying which items we want (hamburger/fries or city/state), where we

want it from (value menu or Customers table), and some extra instructions (make it to go, or

sort the results by state).

But before we get started, let’s address one minor point: how to pronounce the word SQL. It

turns out that there are two choices. One option is to simply to say it as individual letters, like

“S-Q-L.” Another possibility, preferred by the author, is to pronounce it as the word “sequel.”

This is one less syllable, and a little easier to say. However, there’s no real agreement on the

question. It’s basically a matter of personal preference.

As for what the letters S-Q-L mean, most agree that they stand for “Structured Query

Language.” However, even here, there is not total agreement. Some would argue that SQL

stands for nothing at all, since the language is derived from an old language from IBM called

sequel, which did not, in fact, stand for structured query language.

What Is SQL?

So what is SQL? In a nutshell, SQL is a standard computer language for maintaining 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 development 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 statements that 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.

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 much the same for all vendors. That base language is what we’ll cover

in this book.

As a computer language, SQL is different from other languages you may be familiar with, such

as Visual Basic or C++. These languages tend to be procedural in nature, meaning that they allow

you to specify specific 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 because it is concerned only with relational databases rather than

the entirety of computer systems.

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Microsoft SQL Server, MySQL, and Oracle

One additional point of clarification about the SQL language is that it is sometimes confused

with specific SQL databases. Many software companies sell database management systems

(DBMS) software. In common usage, the databases in these types of software packages are often

referred to as SQL databases, because 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 database SQL Server 2016. But in fact, SQL is more

properly a language than a database. Our focus in this book is on the language of SQL rather

than on any particular database.

Microsoft SQL Server, MySQL, and Oracle

Although our aim is to cover the core language of SQL as it applies to all implementations,

wemust ultimately also provide specific examples of SQL syntax. And because syntax does

varysomewhat among vendors, we’ve decided to focus on the SQL syntax utilized by these

three popular databases:

• Microsoft SQL Server

• MySQL

• Oracle

In most cases, these databases have the same syntax. However, there are occasional differences.

If there is any variance between these databases, the syntax for Microsoft SQL Server will be

presented in the main text of this book. Any differences for MySQL or Oracle will be indicated

in a sidebar titled “Database Differences,” as shown here:

Database Differences

A sidebar such as this will appear whenever there are syntax differences for MySQL or Oracle.

The syntax for Microsoft SQL Server will appear in the main text.

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

is called Microsoft SQL Server 2016. 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 users to get started with full-fledged database development. The Enterprise

edition includes many sophisticated database management features, plus powerful business

intelligencecomponents.

Although owned by Oracle, MySQL is an open-source database, which means that no single

organization controls its development. 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. The most recent version is MySQL 5.7.

The Oracle database is available in several editions. The most recent version is called Oracle

Database 12c. The free version of the database is called the Express edition.

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