SQL视觉快速入门指南第三版

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"《SQL视觉快速入门指南》第三版是由Chris Fehily所著，由Peachpit Press出版的一本实用教程。本书是针对想要快速学习和理解SQL语言的读者精心设计的，旨在帮助读者通过直观、视觉化的学习方式掌握SQL的核心概念和技术。作为第三版，它可能包含对SQL新版本的更新和改进，以及对数据库管理系统（DBMS）操作的深入讲解。书中涵盖了SQL的基础知识，如查询构造、数据表管理、视图和存储过程等，适合初学者和有一定经验的开发者用来巩固或提升技能。作者以其清晰易懂的写作风格，配合图表和实例，使得复杂的SQL语句变得通俗易懂。此外，书中还可能包括如何在实际项目中应用SQL，以及如何解决常见的性能优化问题。版权方面，本书受到严格保护，未经Pearson Education和Peachpit Press的书面许可，任何形式的复制或传播都必须得到授权。错误报告通道已经提供，读者可以通过errata@peachpit.com提交发现的问题，以确保内容的准确性和完整性。同时，书中的所有信息是以“无责任”基础提供的，尽管编辑和作者已尽最大努力确保信息的准确性，但不承担因使用本书内容产生的任何责任。《SQL视觉快速入门指南》第三版是一本非常适合SQL学习者的实用工具书，无论是为了初次接触SQL，还是希望提升现有技能，都能从中获得有价值的指导。"

SQL to be synonymous unless I note other-

wise. For more information, see “SQL

Standards and Conformance” in Chapter 3.

All DBMS vendors add proprietary features

to standard SQL to enhance the language.

These extensions usually are additional com-

mands, keywords, functions, operators, data

types, and control-flow constructs such as

while

, and

goto

statements. Microsoft,

Oracle, and IBM have added so many features

to standard SQL that the resulting languages—

Transact-SQL, PL/SQL, and SQL PL, respec-

tively—can be considered to be separate

languages in their own right, rather than

just supersets of SQL. One vendor’s exten-

sions generally are incompatible with other

vendors’ products. I don’t cover proprietary

SQL extensions, but I do point out when a

vendor’s SQL dialect doesn’t comply with

the standard SQL examples in this book;

see “Using SQL with a specific DBMS” later

in this introduction.

Used to change data and database

objects. SQL statements are divided into

three categories:

◆

Data manipulation language (DML)

statements retrieve, reckon, insert, edit,

and delete data stored in a database.

Chapters 4 through 10 cover the DML

statements

SELECT

INSERT

UPDATE

, and

DELETE

. Chapter 14 covers

START

(or

BEGIN

COMMIT

, and

ROLLBACK

◆

Data definition language (DDL) state-

ments create, modify, and destroy database

objects such as tables, indexes, and

views. Chapters 11 through 13 cover the

DDL statements

CREATE

ALTER

, and

DROP

◆

Data control language (DCL) statements

authorize certain users to view, change,

or delete data and database objects. The

GRANT

statement assigns privileges to

users and roles (a role is a named set of

privileges). The

REVOKE

statement removes

privileges.

GRANT

and

REVOKE

aren’t covered

in this book because they’re the respon-

sibility of database administrators.

All the DBMSs (except Access) covered

in this book support

GRANT

and

REVOKE

with variations on the SQL standard.

Not an acronym. It’s a common miscon-

ception that SQL stands for structured query

language; it stands for S–Q–L and nothing

else. Why? Because ANSI says so. The offi-

cial name is Database Language SQL (refer

to Figure i.1). Furthermore, referring to it as

a structured query language is a disservice

to new SQL programmers. It amuses insiders

to point out that “structured query lan-

guage” is the worst possible description,

because SQL:

◆

Isn’t structured (because it can’t be bro-

ken down into blocks or procedures)

◆

Isn’t for only queries (because it has

more than just the

SELECT

statement)

◆

Isn’t a language (because it’s not Turing-

complete, which you’ll study should you

take Theory of Computation)

Introduction

About SQL

Audience

My audience is database-application pro-

grammers and database end-users (not

database designers or administrators), so

this book is appropriate for you if you:

◆

Lack programming experience but are

familiar with computers.

◆

Are learning SQL on your own or from

an instructor.

◆

Are otherwise uninterested in databases

but must process large amounts of struc-

tured information because of the nature

of your work. This group includes statisti-

cians, epidemiologists, web programmers,

meteorologists, engineers, accountants,

investigators, scientists, analysts, sales

reps, financial planners and traders, office

managers, and managers.

◆

Want to move beyond friendly but

underpowered graphical query tools.

◆

Are moving from a desktop to a server

DBMS (see the sidebar in this section).

◆

Already know some SQL and want to

move past simple

SELECT

statements.

◆

Need to create, change, or delete data-

base objects such as tables, indexes,

and views.

◆

Need to embed SQL code in C, Java, Visual

Basic, PHP, Perl, or other host languages.

◆

Are a web programmer and need to dis-

play query results on web pages.

◆

Need a desktop SQL reference book.

◆

Are migrating from Microsoft Excel

to Access because your data lists have

grown too big or complex to manage

in a spreadsheet.

xvii

Introduction

About This Book

SQL Server vs. Desktop DBMSs

An SQL server DBMS acts as the server

part of a client/server network; it stores

databases and responds to SQL requests

made by many clients. A client is an appli-

cation or computer that sends an SQL

request to a server and accepts the serv-

er’s response. The server does the actual

work of executing the SQL against a data-

base; the client merely accepts the answer.

If your network uses a client/server archi-

tecture, the client is the computer on

your desk, and the server is a powerful,

specialized machine in another room,

building, or country. The rules that

describe how client/server requests and

responses are transmitted are part of

DBMS protocols and interfaces such as

ODBC, JDBC, and ADO.NET.

A desktop DBMS is a stand-alone pro-

gram that can store a database and do all

the SQL processing itself or behave as a

client of an SQL server. A desktop DBMS

can’t accept requests from other clients

(that is, it can’t act like an SQL server).

SQL servers include Microsoft SQL Server,

Oracle, DB2, MySQL, and PostgreSQL.

Desktop systems include Microsoft Access

and FileMaker Pro. Note that SQL server

(not capitalized) can refer to any vendor’s

SQL server product, and SQL Server (capi-

talized) is Microsoft’s particular SQL server

product. By convention, I use client and

server to refer to client and server soft-

ware itself or to the machine on which

the software runs, unless the distinction

is important.

This book is not appropriate for you if you

want to learn:

◆

How to design databases (although I

review proper design concepts in

Chapter 2).

◆

Proprietary extensions that DBMS ven-

dors add beyond the basic SQL statements.

◆

Advanced programming or administra-

tion. I don’t cover installation, privileges,

triggers, recursion,* stored procedures,

replication, backup and recovery, cursors,

collations, character sets, translations,

XML, or object-oriented extensions.

Typographic conventions

I use the following typographic conventions:

Italic type introduces new terms or repre-

sents replaceable variables in regular text.

Monospace type

denotes SQL code and

syntax in listings and in regular text. It also

shows executables, filenames, directory

(folder) names, URLs, and command-

prompt text.

Red monospace type

highlights SQL code

fragments and results that are explained in

the accompanying text.

Italic monospace type

denotes a variable in

SQL code that you must replace with a

value. You’d replace

column

with the name of

an actual column, for example.

Syntax conventions

SQL is a free-form language without restric-

tions on line breaks or the number of words

per line, so I use a consistent style in SQL

syntax diagrams and code listings to make

the code easy to read and maintain:

◆

Each SQL statement begins on a

new line.

◆

The indentation level is two spaces.

◆

Each clause of a statement begins on a

new, indented line:

SELECT au_fname, au_lname

FROM authors

ORDER BY au_lname;

◆

SQL is case insensitive, which means

that

myname

MyName

, and

MYNAME

are con-

sidered to be identical identifiers. I use

UPPERCASE

for SQL keywords such as

SELECT

NULL

, and

CHARACTER

(see “SQL

Syntax” in Chapter 3), and

lowercase

lower_case

for user-defined values, such

as table, column, and alias names.

(User-defined identifiers are case sensitive

when quoted and in a few other situations

for some DBMSs, so it’s safest to respect

identifier case in SQL programs.)

◆

Table i.1 shows special symbols that I

use in syntax diagrams.

◆

All quote marks in SQL code are straight

quotes (such as

‘

and

“

), not curly, or

smart, quotes (such as ’ and “). Curly

quotes prevent code from working.

◆

When a column is too narrow to hold a

single line of code or output, I break it

into two or more segments. A gray arrow

➝

indicates a continued line.

xviii

Introduction

About This Book

* To understand recursion, you first must understand

recursion.

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SQL视觉快速入门指南第三版

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