SQL and Relational Theory: How to Write Accurate SQL Code PDF
Preview SQL and Relational Theory: How to Write Accurate SQL Code
Download at WoweBook.Com SQL and Relational Theory How to Write Accurate SQL Code Download at WoweBook.Com Other resources from O’Reilly Related titles The Art of SQL Essential SQLAlchemy Database In Depth SQL in a Nutshell oreilly.com oreilly.com is more than a complete catalog of O’Reilly books. You’ll also find links to news, events, articles, weblogs, sample chapters, and code examples. oreillynet.comistheessentialportalfordevelopersinterested in open and emerging technologies, including new plat- forms, programming languages, and operating systems. Conferences O’Reilly brings diverse innovators together to nurture the ideas that spark revolutionary industries. We specialize in documenting the latest tools and systems, translating the innovator’s knowledge into useful skills for those in the trenches. Visit conferences.oreilly.com for our upcoming events. Safari Bookshelf (safari.oreilly.com) is the premier online reference library for programmers and IT professionals. Conduct searches across more than 1,000 books. Sub- scribers can zero in on answers to time-critical questions inamatterofseconds.ReadthebooksonyourBookshelf from cover to cover or simply flip to the page you need. Try it today for free. Download at WoweBook.Com SQL and Relational Theory How to Write Accurate SQL Code C. J. Date Beijing • Cambridge • Farnham • Köln • Sebastopol • Taipei • Tokyo Download at WoweBook.Com SQL and Relational Theory: How to Write Accurate SQL Code by C. J. Date Copyright © 2009 Chris Date. All rights reserved. Printed in the United States of America. Published by O’Reilly Media, Inc. 1005 Gravenstein Highway North, Sebastopol, CA 95472 O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (safari.oreilly.com). For more information, contact our corporate/institutional sales department: (800)998-9938 or [email protected]. Editor: Andy Oram Cover Designer: Mark Paglietti Production Editor: Adam Witwer Interior Designer: Marcia Friedman Indexer: C.J. Date Illustrators: Jessamyn Read Printing History: January 2009: First Edition. The O’Reilly logo is a registered trademark of O’ReillyMedia, Inc.SQL and Relational Theory and related trade dress are trademarks of O’Reilly Media, Inc. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps. While every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. ISBN: 978-0-596-52306-0 [V] Download at WoweBook.Com Toallthosewhothinkanexerciselikethis one is worthwhile, and in particular to the memory of Lex de Haan, who is very much missed. Those who are enamored of practice without theory are like a pilot who goes into a ship without rudder or compass and never has any certainty where he is going. Practice should always be based upon a sound knowledge of theory. Leonardo da Vinci (1452–1519) The trouble with people is not that they don’t know but that they know so much that ain’t so. Josh Billings (1818–1885) Languages die… mathematical ideas do not. G. H. Hardy Unfortunately, the gap between theory and practice is not as wide in theory as it is in practice. Anonymous Download at WoweBook.Com Download at WoweBook.Com CO NTENTS PREFACE xiii 1 SETTING THE SCENE 1 The Relational Model Is Much Misunderstood 2 Some Remarks on Terminology 3 Principles, Not Products 4 A Review of the Original Model 5 Model vs. Implementation 13 Properties of Relations 17 Base vs. Derived Relations 19 Relations vs. Relvars 21 Values vs. Variables 23 Concluding Remarks 24 Exercises 25 2 TYPES AND DOMAINS 27 Types and Relations 27 Equality Comparisons 28 Data Value Atomicity 34 What’s a Type? 37 Scalar vs. Nonscalar Types 40 Scalar Types in SQL 42 Type Checking and Coercion in SQL 43 Collations in SQL 45 Row and Table Types in SQL 47 Concluding Remarks 49 Exercises 50 3 TUPLES AND RELATIONS, ROWS AND TABLES 53 What’s a Tuple? 53 Rows in SQL 57 What’s a Relation? 60 Relations and Their Bodies 61 Relations Are n-Dimensional 62 Relational Comparisons 63 TABLE_DUM and TABLE_DEE 64 Tables in SQL 65 vii Download at WoweBook.Com Column Naming in SQL 66 Concluding Remarks 68 Exercises 69 4 NO DUPLICATES, NO NULLS 71 What’s Wrong with Duplicates? 71 Duplicates: Further Issues 76 Avoiding Duplicates in SQL 77 What’s Wrong with Nulls? 79 Avoiding Nulls in SQL 82 A Remark on Outer Join 84 Concluding Remarks 85 Exercises 86 5 BASE RELVARS, BASE TABLES 89 Data Definitions 90 Updating Is Set Level 90 Relational Assignment 92 More on Candidate Keys 94 More on Foreign Keys 97 Relvars and Predicates 100 Relations vs. Types 102 Exercises 105 6 SQL AND RELATIONAL ALGEBRA I: THE ORIGINAL OPERATORS 107 Some Preliminaries 107 More on Closure 110 Restriction 113 Projection 114 Join 115 Union, Intersection, and Difference 118 Which Operators Are Primitive? 120 Formulating Expressions a Step at a Time 121 What Do Relational Expressions Mean? 122 Evaluating SQL Table Expressions 123 Expression Transformation 124 The Reliance on Attribute Names 127 Exercises 129 viii CONTENTS Download at WoweBook.Com
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