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SQL and Relational Theory, 2nd Edition

How to Write Accurate SQL Code

By Chris Date

Publisher: O'Reilly Media

Release Date: December 2011

Pages: 448

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SQL is full of difficulties and traps for the unwary. You can avoid them if you understand relational theory, but only if you know how to put the theory into practice. In this insightful book, author C.J. Date explains relational theory in depth, and demonstrates through numerous examples and exercises how you can apply it directly to your use of SQL.

This second edition includes new material on recursive queries, “missing information” without nulls, new update operators, and topics such as aggregate operators, grouping and ungrouping, and view updating. If you have a modest-to-advanced background in SQL, you’ll learn how to deal with a host of common SQL dilemmas.

Why is proper column naming so important?
Nulls in your database are causing you to get wrong answers. Why? What can you do about it?
Is it possible to write an SQL query to find employees who have never been in the same department for more than six months at a time?
SQL supports “quantified comparisons,” but they’re better avoided. Why? How do you avoid them?
Constraints are crucially important, but most SQL products don’t support them properly. What can you do to resolve this situation?

Database theory and practice have evolved since the relational model was developed more than 40 years ago. SQL and Relational Theory draws on decades of research to present the most up-to-date treatment of SQL available.

C.J. Date has a stature that is unique within the database industry. A prolific writer well known for the bestselling textbook An Introduction to Database Systems (Addison-Wesley), he has an exceptionally clear style when writing about complex principles and theory.

Chapter 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
6. PROPERTIES OF RELATIONS
7. BASE vs. DERIVED RELATIONS
8. RELATIONS vs. RELVARS
9. VALUES vs. VARIABLES
10. CONCLUDING REMARKS
11. EXERCISES
Chapter 2 Types and Domains
1. TYPES AND RELATIONS
2. EQUALITY COMPARISONS
3. DATA VALUE ATOMICITY
4. WHAT’S A TYPE?
5. SCALAR vs. NONSCALAR TYPES
6. SCALAR TYPES IN SQL
7. TYPE CHECKING AND COERCION IN SQL
8. COLLATIONS IN SQL
9. ROW AND TABLE TYPES IN SQL
10. CONCLUDING REMARKS
11. EXERCISES
Chapter 3 Tuples and Relations, Rows and Tables
1. WHAT’S A TUPLE?
2. ROWS IN SQL
3. WHAT’S A RELATION?
4. RELATIONS AND THEIR BODIES
5. RELATIONS ARE n-DIMENSIONAL
6. RELATIONAL COMPARISONS
7. TABLE_DUM AND TABLE_DEE
8. TABLES IN SQL
9. COLUMN NAMING IN SQL
10. CONCLUDING REMARKS
11. EXERCISES
Chapter 4 No Duplicates, No Nulls
1. WHAT’S WRONG WITH DUPLICATES?
2. DUPLICATES: FURTHER ISSUES
3. AVOIDING DUPLICATES IN SQL
4. WHAT’S WRONG WITH NULLS?
5. AVOIDING NULLS IN SQL
6. A REMARK ON OUTER JOIN
7. CONCLUDING REMARKS
8. EXERCISES
Chapter 5 Base Relvars, Base Tables
1. UPDATING IS SET LEVEL
2. RELATIONAL ASSIGNMENT
3. MORE ON CANDIDATE KEYS
4. MORE ON FOREIGN KEYS
5. RELVARS AND PREDICATES
6. RELATIONS vs. TYPES
7. EXERCISES
Chapter 6 SQL and Relational Algebra I: The Original Operators
1. SOME PRELIMINARIES
2. MORE ON CLOSURE
3. RESTRICTION
4. PROJECTION
5. JOIN
6. UNION, INTERSECTION, AND DIFFERENCE
7. WHICH OPERATORS ARE PRIMITIVE?
8. FORMULATING EXPRESSIONS ONE STEP AT A TIME
9. WHAT DO RELATIONAL EXPRESSIONS MEAN?
10. EVALUATING SQL TABLE EXPRESSIONS
11. EXPRESSION TRANSFORMATION
12. THE RELIANCE ON ATTRIBUTE NAMES
13. EXERCISES
Chapter 7 SQL and Relational Algebra II : Additional Operators
1. EXCLUSIVE UNION
2. SEMIJOIN AND SEMIDIFFERENCE
3. EXTEND
4. IMAGE RELATIONS
5. DIVIDE
6. AGGREGATE OPERATORS
7. IMAGE RELATIONS bis
8. SUMMARIZATION
9. SUMMARIZATION bis
10. GROUP, UNGROUP, AND RELATION VALUED ATTRIBUTES
11. “WHAT IF” QUERIES
12. A NOTE ON RECURSION
13. WHAT ABOUT ORDER BY?
14. EXERCISES
Chapter 8 SQL and Constraints
1. TYPE CONSTRAINTS
2. TYPE CONSTRAINTS IN SQL
3. DATABASE CONSTRAINTS
4. DATABASE CONSTRAINTS IN SQL
5. TRANSACTIONS
6. WHY DATABASE CONSTRAINT CHECKING MUST BE IMMEDIATE
7. BUT DOESN’T SOME CHECKING HAVE TO BE DEFERRED?
8. CONSTRAINTS AND PREDICATES
9. MISCELLANEOUS ISSUES
10. EXERCISES
Chapter 9 SQL and Views
1. VIEWS ARE RELVARS
2. VIEWS AND PREDICATES
3. RETRIEVAL OPERATIONS
4. VIEWS AND CONSTRAINTS
5. UPDATE OPERATIONS
6. WHAT ARE VIEWS FOR?
7. VIEWS AND SNAPSHOTS
8. EXERCISES
Chapter 10 SQL and Logic
1. WHY DO WE NEED LOGIC?
2. SIMPLE AND COMPOUND PROPOSITIONS
3. SIMPLE AND COMPOUND PREDICATES
4. QUANTIFICATION
5. RELATIONAL CALCULUS
6. MORE ON QUANTIFICATION
7. SOME EQUIVALENCES
8. CONCLUDING REMARKS
9. EXERCISES
Chapter 11 Using Logic to Formulate SQL Expressions
1. SOME TRANSFORMATION LAWS
2. EXAMPLE 1: LOGICAL IMPLICATION
3. EXAMPLE 2: UNIVERSAL QUANTIFICATION
4. EXAMPLE 3: IMPLICATION AND UNIVERSAL QUANTIFICATION
5. EXAMPLE 4: CORRELATED SUBQUERIES
6. EXAMPLE 5: NAMING SUBEXPRESSIONS
7. EXAMPLE 6: MORE ON NAMING SUBEXPRESSIONS
8. EXAMPLE 7: DEALING WITH AMBIGUITY
9. EXAMPLE 8: USING COUNT
10. EXAMPLE 9: JOIN QUERIES
11. EXAMPLE 10: UNIQUE QUANTIFICATION
12. EXAMPLE 11: ALL OR ANY COMPARISONS
13. EXAMPLE 12: GROUP BY AND HAVING
14. EXERCISES
Chapter 12 Miscellaneous SQL Topics
1. SELECT *
2. EXPLICIT TABLES
3. NAME QUALIFICATION
4. RANGE VARIABLES
5. SUBQUERIES
6. “POSSIBLY NONDETERMINISTIC” EXPRESSIONS
7. EMPTY SETS
8. A SIMPLIFIED BNF GRAMMAR
9. EXERCISES

Appendix The Relational Model
1. THE RELATIONAL MODEL vs. OTHERS
2. THE SIGNIFICANCE OF THEORY
3. THE RELATIONAL MODEL DEFINED
4. DATABASE VARIABLES
5. OBJECTIVES OF THE RELATIONAL MODEL
6. SOME DATABASE PRINCIPLES
7. WHAT REMAINS TO BE DONE?
Appendix SQL Departures from the Relational Model
Appendix A Relational Approach to Missing Information
1. VERTICAL DECOMPOSITION
2. HORIZONTAL DECOMPOSITION
3. WHAT DO THE SHADED ENTRIES MEAN?
4. CONSTRAINTS
5. QUERIES
6. MORE ON PREDICATES
7. EXERCISES
Appendix A Tutorial D Grammar
Appendix Summary of Recommendations
Appendix Answers to Exercises
1. CHAPTER 1
2. CHAPTER 2
3. CHAPTER 3
4. CHAPTER 4
5. CHAPTER 5
6. CHAPTER 6
7. CHAPTER 7
8. CHAPTER 8
9. CHAPTER 9
10. CHAPTER 10
11. CHAPTER 11
12. CHAPTER 12
13. APPENDIX C
Appendix Suggestions for Further Reading

Books & Videos

SQL and Relational Theory, 2nd Edition

How to Write Accurate SQL Code

Read on Safari with a 10-day trial

Table of Contents

Chapter 1 Setting the Scene

THE RELATIONAL MODEL IS MUCH MISUNDERSTOOD

SOME REMARKS ON TERMINOLOGY

PRINCIPLES NOT PRODUCTS

A REVIEW OF THE ORIGINAL MODEL

MODEL vs. IMPLEMENTATION

PROPERTIES OF RELATIONS

BASE vs. DERIVED RELATIONS

RELATIONS vs. RELVARS

VALUES vs. VARIABLES

CONCLUDING REMARKS

EXERCISES

Chapter 2 Types and Domains

TYPES AND RELATIONS

EQUALITY COMPARISONS

DATA VALUE ATOMICITY

WHAT’S A TYPE?

SCALAR vs. NONSCALAR TYPES

SCALAR TYPES IN SQL

TYPE CHECKING AND COERCION IN SQL

COLLATIONS IN SQL

ROW AND TABLE TYPES IN SQL

CONCLUDING REMARKS

EXERCISES

Chapter 3 Tuples and Relations, Rows and Tables

WHAT’S A TUPLE?

ROWS IN SQL

WHAT’S A RELATION?

RELATIONS AND THEIR BODIES

RELATIONS ARE n-DIMENSIONAL

RELATIONAL COMPARISONS

TABLE_DUM AND TABLE_DEE

TABLES IN SQL

COLUMN NAMING IN SQL

CONCLUDING REMARKS

EXERCISES

Chapter 4 No Duplicates, No Nulls

WHAT’S WRONG WITH DUPLICATES?

DUPLICATES: FURTHER ISSUES

AVOIDING DUPLICATES IN SQL

WHAT’S WRONG WITH NULLS?

AVOIDING NULLS IN SQL

A REMARK ON OUTER JOIN

CONCLUDING REMARKS

EXERCISES

Chapter 5 Base Relvars, Base Tables

UPDATING IS SET LEVEL

RELATIONAL ASSIGNMENT

MORE ON CANDIDATE KEYS

MORE ON FOREIGN KEYS

RELVARS AND PREDICATES

RELATIONS vs. TYPES

EXERCISES

Chapter 6 SQL and Relational Algebra I: The Original Operators

SOME PRELIMINARIES

MORE ON CLOSURE

RESTRICTION

PROJECTION

JOIN

UNION, INTERSECTION, AND DIFFERENCE

WHICH OPERATORS ARE PRIMITIVE?

FORMULATING EXPRESSIONS ONE STEP AT A TIME

WHAT DO RELATIONAL EXPRESSIONS MEAN?

EVALUATING SQL TABLE EXPRESSIONS

EXPRESSION TRANSFORMATION

THE RELIANCE ON ATTRIBUTE NAMES

EXERCISES

Chapter 7 SQL and Relational Algebra II : Additional Operators

EXCLUSIVE UNION

SEMIJOIN AND SEMIDIFFERENCE

EXTEND

IMAGE RELATIONS

DIVIDE

AGGREGATE OPERATORS

IMAGE RELATIONS bis