Oracle PL/SQL编程指南

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"Oracle.PLSQL(2001)].Bill.Pribyl." Oracle PL/SQL是一种强大的编程语言，用于在Oracle数据库环境中创建和管理复杂的应用程序。由Bill Pribyl和Steven Feuerstein合作编写的《Learning Oracle PL/SQL》是学习这一语言的重要参考资料，旨在帮助开发者理解和掌握Oracle数据库中的过程式SQL。本书主要涵盖以下几个关键知识点： 1. **基础语法**：PL/SQL的基础包括变量声明、常量、数据类型、运算符和控制结构。读者将学习如何声明并初始化变量，以及如何使用条件语句（如IF-THEN-ELSE）和循环（如FOR，WHILE）来控制程序流程。 2. **块结构**：PL/SQL代码通常组织成块，包括声明部分、执行部分和异常处理部分。理解块的结构对于编写有效和可维护的代码至关重要。 3. **过程与函数**：PL/SQL允许创建自定义过程和函数，它们可以存储在数据库中并重复使用。这有助于提高代码复用性和效率。 4. **游标**：游标是处理单行结果集的关键工具，用于在查询返回的多行数据中逐行操作。书中会详细介绍如何声明、打开、提取数据和关闭游标。 5. **异常处理**：PL/SQL提供了内置的异常处理机制，允许开发者优雅地处理错误，避免程序中断。了解何时使用RAISE、WHENEVER和EXCEPTION关键字对于编写健壮的代码至关重要。 6. **数据库对象**：PL/SQL可以创建、修改和操作数据库对象，如表、视图、索引、触发器和存储过程。这使得开发者能够直接在数据库级别实现业务逻辑。 7. **事务管理**：事务控制是数据库操作的核心，包括COMMIT、ROLLBACK和SAVEPOINT。书中会解释如何确保数据的一致性和完整性。 8. **性能优化**：通过索引、子查询优化、批量操作和绑定变量，开发者可以学习如何提高PL/SQL代码的运行效率。 9. **动态SQL**：动态SQL允许在运行时构建和执行SQL语句，这对于处理不确定的查询需求或复杂的数据库交互非常有用。 10. **最佳实践**：书中可能包含编写高效、可读性强且易于维护的PL/SQL代码的最佳实践和指导原则。《Learning Oracle PL/SQL》是一本面向初学者和有经验的数据库开发者的教材，它深入浅出地介绍了Oracle数据库中的过程编程，并通过实例帮助读者巩固所学知识。无论是为了提升个人技能，还是为了更好地理解和维护现有的Oracle数据库应用，这本书都是一份宝贵的资源。

This is the Title of the Book, eMatter Edition

xiv

Preface

As a beginner’s tool, this book will expose you to the most important features of PL/

SQL, but without burrowing into the depths of exotic version-specific features. I do

make heavy use of PL/SQL Server Pages starting with Chapter 4. Although this fea-

ture became available only when Oracle shipped Version 8.1.6 (an update to

Oracle8i) the syntax was previously available in other Oracle web-based products

such as Oracle WebServer and Oracle Application Server.

If you still have to work with Oracle7—a version of the server that Oracle Corpora-

tion treats as virtually obsolete—many of the features we discuss will still be useful

to you, but primarily as negotiating points you might use to encourage your com-

pany to upgrade.

Organization of This Book

Learning Oracle PL/SQL differs from other PL/SQL books in several important ways:

Kinder, gentler organization

Other programming books are often organized around language features, with a

chapter for datatypes, one for loops, and another for exceptions. Such a “feature-

oriented” volume works fine if you already know roughly how you want to

accomplish a given programming task—you flip to the part of the book that cov-

ers the technique you want to use. And, if you don’t quite know how you want

to solve your problem, you merely read the book from cover to cover and assimi-

late its entire contents. Or not.

In contrast, the chapters in this book are arranged in order of increasing com-

plexity, each chapter building on the previous one. I encourage you to read this

book straight through, from front to back (or at least as far as you can get),

rather than leaf or browse through it as you would a reference book.

The fact is that if you’re just getting started with a new language, you are

unlikely to know what features you will need to use to accomplish your pro-

gramming goals (even if you do know what your programming goals are). When

this book presents a new language topic, it usually appears in the context of a

given functional objective. So, for example, to introduce the idea of PL/SQL

packages, we didn’t write a separate chapter about packages that documents the

syntax and throws in some contrived examples. Instead, the book proceeds

along with the business of developing a specific application and introduces pack-

ages as a solution to a problem.

Single, coordinated example

A second difference between this book and other PL/SQL books is that Learning

Oracle PL/SQL develops and uses one set of tables and one application system as

* Well, this is the general goal, anyway. Chapter 2 is not like that at all.

This is the Title of the Book, eMatter Edition

Preface

the source of almost all of its code. We start with a simplified version of the sys-

tem—a library’s electronic catalog system—and add complexity in later chapters.

Glossary

A third unique feature of Learning Oracle PL/SQL is the Glossary, which begin-

ners should find very helpful (note, though, that you can find most new terms

defined when they first appear in the text).

The first two chapters of this book present PL/SQL language basics. These chapters

set the stage for the remainder of the book.

Chapter 1, PL/SQL: What, When, and Where, provides an introduction to the lan-

guage: what it is, why it exists, and when it is useful. Here you’ll find a list of PL/

SQL’s unique advantages, plus a frank discussion of its limitations. We also intro-

duce the sample application that will be used throughout the book.

Chapter 2, Fundamentals, presents the basics of the language, its core “syntax” and

structure. This is necessary before starting to solve the sample problem. The chapter

contains short code fragments to illustrate concepts, but doesn’t waste time with lit-

tle-used or advanced features. Chapter 2 also contains a primer on how to execute

your PL/SQL code using Oracle’s tool called SQL*Plus.

Chapter 3, Let’s Code!, begins to apply the fundamentals learned in Chapter 2 to the

problem of building the sample application, which is presented in more detail here.

The main application task addressed in this chapter involves adding books to the

catalog.

Chapter 4, Go Web, Young Man, addresses the second part of the “add books” task

introduced in Chapter 3: building a user interface. This chapter presents a way to build

a front-end to the library application, using PL/SQL, of course, as the language in

which to create a web-based user interface. The chapter introduces HTML (the lan-

guage of the Web) and discusses some nonobvious ways you can test your application.

Chapter 5, Fetch!, describes how to create a search system that enables users to query

the library catalog. The main PL/SQL topic addressed in this chapter involves retriev-

ing data from the database and using it inside PL/SQL.

Chapter 6, Keeping House, discusses a topic you may be wondering about by the

time you get there: aren’t there tools to help me write these programs? This chapter

covers some ways you might want to accelerate your development effort by using

tools like a full-featured programmer’s editor, a commercial “interactive develop-

ment environment” (IDE), or a debugger. It also discusses several “lower tech”

approaches that can save you time and effort.

Chapter 7, Security: Keep the Bad Guys Out, looks at the overall problem of security.

How can we let authorized users, and only authorized users, use our library catalog

system? How can we use PL/SQL to track changes made to the system (an audit trail)?

What features can help us build adequate privacy controls into our application?

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Preface

Chapter 8, Communicating with the Outside World, covers some of the issues

involved in communicating with the outside world. No system is an island, and PL/

SQL provides tools that will help you do things like send email to Internet addresses,

fetch data from other web pages, and read data from files. This chapter also takes a

very brief look at calling programs written in Java and C from PL/SQL.

Chapter 9, Intermediate Topics and Other Diversions, contains material that you will

find useful as you master the basics and move on to do more complex PL/SQL pro-

gramming.

Afterword: “Making Good” of Database Programming, is a personal essay in which I

explore some of the ethical considerations that you may face as a database applica-

tion developer in the twenty-first century. I believe that some consideration of this

topic, even though it is generally ignored in technical books, helps keep technology

in its proper place: under the dominion and service of humans rather than the other

way around.

The Glossary is a listing of the many terms used in this book and in PL/SQL pro-

gramming.

We leave you, the beginning PL/SQL programmer, to be the final judge of how effec-

tively this book helps you learn to program in PL/SQL. We invite your feedback.

Please see “Comments and Questions” for how you can contact us.

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Used for the names of files and directories. It is also used for URLs, for empha-

sis, and for the first use of a technical term.

Constant width

Used for code examples, the names of columns, variables, tables, procedures,

functions, and packages, and to show the contents of files and the output of

commands.

Constant width italic

Used in syntax descriptions or other places to indicate where user-supplied (or

programmer-supplied) text would appear.

Constant width bold

Indicates user input in examples showing an interaction. Also used in some pro-

gramming examples to highlight code fragments explained by neighboring para-

graphs.

UPPERCASE

In syntax descriptions and source code, usually indicates keywords.

This is the Title of the Book, eMatter Edition

xviii

Preface

We have a web site for this book, where you can find the full code for the sample

application described in this book. There you will also find errata (previously

reported errors and corrections are available for public view there). You can visit this

page at:

http://www.oreilly.com/catalog/learnoracle

For more information about this book and others, see the O’Reilly web site:

http://www.oreilly.com

Acknowledgments

No book on PL/SQL could come into existence without a team of people pulling

together. We are indebted to all who have helped turn this idea into a reality.

From Bill

Thanks to Steven for letting me take the lead on this one. You should know that

some of the best prose in the book sprang forth from his prolific pen. It’s hard to

say how many times he read all the words that I wrote for this book, but based on

the volume of comments he supplied on (and the resulting improvements in) the

text, his reputation as “one of the world’s leading experts on PL/SQL” remains

unchallenged.

Dave Hay, data modeler par excellence, helped me understand library data based on

a model from a class that he teaches, while Melinda Flannery of Rice University’s

Fondren Library gave me some additional guidance in the real world. Although the

data model and application in the book don’t even come close to the depth and com-

plexity required in a real library, Dave and Melinda at least gave me an idea of how

much I need to apologize for this fact.

Technical reviewer Corrie Nettles was thankfully brazen in contributing insights

from her perspective as a complete newcomer to PL/SQL. She reminded me about

issues faced when learning the language that I could not have remembered any other

way.

Two (unrelated) PL/SQL instructors provided some great feedback on the book: Mir-

iam Moran and Ron Martini. Contributing insights gleaned from their many hours

teaching the language, their knowledge of the PL/SQL student’s mindset was invalu-

able. Miriam in particular read the book in great detail, issuing forth insightful com-

ments and helpful suggestions throughout.

Bill Phillips and Jose Montoya also reviewed portions of the book from the perspec-

tive of software professionals already competent with other programming languages.

I’m grateful to have received the fruit of their experience, and the book is much better

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