SQL and Relational Theory: How to Write Accurate SQL Code

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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 numerousexamples 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.

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C.J. Date has a stature that is unique within the database industry. C.J. is a prolific writer, and is well-known for his best-selling textbook: An Introduction to Database Systems (Addison Wesley). C.J. is an exceptionally clear-thinking writer who can lay out principles and theory in a way easily understood by his audience. 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     SUMMARIZATION     SUMMARIZATION bis     GROUP, UNGROUP, AND RELATION VALUED ATTRIBUTES     “WHAT IF” QUERIES     A NOTE ON RECURSION     WHAT ABOUT ORDER BY?     EXERCISES Chapter 8 SQL and Constraints     TYPE CONSTRAINTS     TYPE CONSTRAINTS IN SQL     DATABASE CONSTRAINTS     DATABASE CONSTRAINTS IN SQL     TRANSACTIONS     WHY DATABASE CONSTRAINT CHECKING MUST BE IMMEDIATE     BUT DOESN’T SOME CHECKING HAVE TO BE DEFERRED?     CONSTRAINTS AND PREDICATES     MISCELLANEOUS ISSUES     EXERCISES Chapter 9 SQL and Views     VIEWS ARE RELVARS     VIEWS AND PREDICATES     RETRIEVAL OPERATIONS     VIEWS AND CONSTRAINTS     UPDATE OPERATIONS     WHAT ARE VIEWS FOR?     VIEWS AND SNAPSHOTS     EXERCISES Chapter 10 SQL and Logic     WHY DO WE NEED LOGIC?     SIMPLEAND COMPOUND PROPOSITIONS     SIMPLE AND COMPOUND PREDICATES     QUANTIFICATION     RELATIONAL CALCULUS     MORE ON QUANTIFICATION     SOME EQUIVALENCES     CONCLUDING REMARKS     EXERCISES Chapter 11 Using Logic to Formulate SQL Expressions     SOME TRANSFORMATION LAWS     EXAMPLE 1: LOGICAL IMPLICATION     EXAMPLE 2: UNIVERSAL QUANTIFICATION     EXAMPLE 3: IMPLICATION AND UNIVERSAL QUANTIFICATION     EXAMPLE 4: CORRELATED SUBQUERIES     EXAMPLE 5: NAMING SUBEXPRESSIONS     EXAMPLE 6: MORE ON NAMING SUBEXPRESSIONS     EXAMPLE 7: DEALING WITH AMBIGUITY     EXAMPLE 8: USING COUNT     EXAMPLE 9: JOIN QUERIES     EXAMPLE 10: UNIQUE QUANTIFICATION     EXAMPLE 11: ALL OR ANY COMPARISONS     EXAMPLE 12: GROUP BY AND HAVING     EXERCISES Chapter 12 Miscellaneous SQL Topics     SELECT *     EXPLICIT TABLES     NAME QUALIFICATION     RANGE VARIABLES     SUBQUERIES     “POSSIBLY NONDETERMINISTIC” EXPRESSIONS     EMPTY SETS     A SIMPLIFIED BNF GRAMMAR     EXERCISES Appendix The Relational Model     THE RELATIONAL MODEL vs. OTHERS     THE SIGNIFICANCE OF THEORY     THE RELATIONAL MODEL DEFINED     DATABASE VARIABLES     OBJECTIVES OF THE RELATIONAL MODEL     SOME DATABASE PRINCIPLES     WHAT REMAINS TO BE DONE? Appendix SQL Departures from the Relational Model Appendix A Relational Approach to Missing Information     VERTICAL DECOMPOSITION     HORIZONTAL DECOMPOSITION     WHAT DO THE SHADED ENTRIES MEAN?     CONSTRAINTS     QUERIES     MORE ON PREDICATES     EXERCISES Appendix A Tutorial D Grammar Appendix Summary of Recommendations Appendix Answers to Exercises     CHAPTER 1     CHAPTER 2     CHAPTER 3     CHAPTER 4     CHAPTER 5     CHAPTER 6     CHAPTER 7     CHAPTER 8     CHAPTER 9     CHAPTER 10     CHAPTER 11     CHAPTER 12     APPENDIX C Appendix Suggestions for Further Reading