Instant SQL Programming

Joe Celko

Wrox Press Ltd.®

INSTANT

Table of Contents Introduction 1

What Can SQL Do for Me? 2 Who Should Use This Book? 2 How To Use This Book 3 What You Should Know 3

Conventions Used 3 Program Code 4 Fonts and Styles 4

Watcom SQL engine 5 Product Details 5 Requirements 5 Installation Instructions 6 Screen Display 6 Error Trapping 8

Tell Us What You Think 8

Chapter 1: The Nature of SQL 11

Procedural Versus Declarative Languages 12 SQL - the Shopper's Language 12

SQL Basics 15 Vendors and the Relational Model 15

Sets Versus Sequences 17 Tables and Files 19 An Example of Structure Considerations 20 Rows 2 1 Columns 22 The Spreadsheet Analogy 22

The SQL Sub-languages 23

Table of Contents

Data Definition Language - DDL 23 Data Manipulation Language- DML 24 Data Control Language - DCL 25

Transaction Control 26 Integrity 26 Interactive SQL Tools 27

Connecting to the Example Database 28 Creating the Connection 28 Logging In to the Database 29 Logging Out of the Database 29 Alternative SQL Systems 29

Introduction to the Example Database 30 Syntax Awareness 3 1

Terminal 32 Non-Terminal 32 Example of Syntax 33

Exercises 39 Summary 40

Chapter 2: Defining a Database 43

Languages and Their Underlying Model 44 The Set IVIodei 44 Schema and Table 45 Common Conceptual Errors 47

Table Terminology 48 Cardinality of a Table 48 Degree of a Table 48 Domain Compatible Data Types 48 Union Compatible Rows 49

Manipulating Tables 49 Guidelines for Defining Schema and Tables 50

Making Rules for Data 50 Create Table Statements 5 1 SQL Data Types 54

Numeric Types 54 Exact Numerics 55 Approximate Numerics 55

Character Types 56 Temporal Data Types 57

The Default Clause 58 Column Constraints 59

Not Null Constraint 60 Check() Constraint 62 Unique and Primary Key Constraints 63

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References 64 Comments 66 The Example Database 67 Other Table Manipulation Commands 73

Drop Table 74 Alter Table 75

Summary 78

Chapter 3: SQL Arithmetic, Logic and the NULL 81

Numeric Type Conversion 82 Rounding and Truncation 82

Rounding 82 Truncation 83

CASTQ or CONVERTO Function 83 Four Function Math 84

Vendor Math Functions 86 Problems of String Equality 86 String Functions 88

The Substring Function 88 The Fold Functions 88 The Trim Function 89 Length and Position 89

Vendor String Functions 90 Reverse 90 Flip 90 Numtowords 91

Displaying Dates 91 Timestamps 91 Times 92 Intervals 92 Date Arithmetic 93 DATE and TIME Functions 93

Week Functions 94 Comparison Operators in SQL 95

Converting Data Types 96 Logic and SQL 97

Boolean Operators for Three Values 98 Unknown Logical Values 99

The Dreaded NULL 100 Arithmetic and NULLS 100 Missing Values 101 What NULLS Are Not! 104 Comparing NULLS 104 Converting Values to and from NULL 105

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Table of Contents

NULLIFO Function 105 COALESCEO Function 106

Concatenating NULLs 106 Advice Time 106 Row Comparisons in SQL-92 107 Other Logical Operators 109

Summary 110

Chapter 4: Keys and Referential Integrity 113

Definition of a Key 114 Types of Keys 115 A Brief Look at Normalization 117

First Normal Form (Inf) 118 Deletion Update and Insertion Anomalies 120

Second Normal Form (2nf) 120 Third Normal Form (3nf) 123 Other Normal Forms 124

The Example Database 125 Referential Integrity and Other Constraints 126

Check Constraint 127 The UNIQUE Constraint 128 The PRIMARY KEY Constraint 130 Foreign Key Constraints 130 Restricts and Cascades 132

Referential Actions 134 Triggers 136

The Example Database: Revisited 137 Summary 140

Chapter 5: Manipulating Database Information 143

The Structure of the Example Database 144

Using the Interactive SQL Engine 145 The INSERT INTO Command 145

Value List Insertion 146 Query Insertion 146

Inserting Data into the Example Database 146 Selective INSERTing 148 Import and Export of Bulk Data 149

Vtyua\H\& av\d Oe\etm& Rows 149 The DELETE FROM Statement 149 The UPDATE Statement 150 The WHERE Clause 151

Summary 154 Exercises 154

Chapter 6: Querying the Database - the SELECT command 157

SELECT Command Basics 158 The Simple Single Table SELECT Statement 161

SELECT and ALTER TABLE 161 Creating New Columns - the AS Operator 163

How the SELECT Statement Works 163 The WHERE Clause 166

Boolean Search Conditions 168 Predicates with the WHERE clause 169

The LIKE Predicate 170 NULLS and Empty Strings 172 The IN Predicate 172 The BETWEEN Predicate 174 IS NULL, IS TRUE, IS FALSE and IS UNKNOWN 176

The ORDER BY Clause 177 Summary 179 Exercises 180

Chapter 7: Joining Tables 183

Two or More Tables in a SELECT Statement 184 Cross Joins 185 Equi Joins 187

An Equi Join Example: at the Bank 187 An Example from the Database 188 Non-equi Joins 190 Theta Joins 191

Self Joins and Aliases 1 9 1 Correlation Names 192 Joining a Table to a Copy of Itself 192 Pitfalls of Self Joins 194 Three Table Joins 197

Joins in SQL-92 Syntax 200 Outer Join in SQL-92 Syntax 2 0 1

Left Outer Join 203 Right Outer Join 204 Full Outer Join 204

Summary 207

Exercises 208

Chapter 8: Grouped Tables and Aggregate Functions 211

Table of Contents

The GROUP BY Clause 2 1 2 The Working Table 212

Common Problems with GROUP BY 216 GROUP BY and NULLS 217

Aggregate Functions in Groups 2 1 8 NULLs in Aggregate Functions 218 The COUNT Functions 219 The SUM Functions 220 The AVG Functions 2 2 2 The Extreme Functions .224

The MAX Function 225 The MIN Function 226

GROUP BY and Aggregate Functions 2 2 7 GROUP BY and HAVING 229

Summary 2 3 1 Exercises 2 3 2

Chapter 9: Using Subqueries 235

Subqueries 2 3 6

Queries with Subquery Predicates 2 3 6 The Nested Scalar Subquery 237 Predicates and Relational Operators 239

The ANY Predicate 239 The ALL Predicate 242

The Correlated Subquery 244 EXISTS <subquery> Predicate 245 Subqueries in the HAVING Clause 248

Using Subquery Predicates in Other Statements 2 4 9 Stand-alone Scalar Subqueries 249 Subqueries in DELETE FROM Statements 250 Subqueries in INSERT Statements 250

Subqueries in UPDATE Statements 2 5 1

Summary 2 5 2

Exercises 2 5 2

Chapter 10: Views 255

Introducing VIEWs 2 5 6 Handling VIEWS 256 The CREATE VIEW Syntax 257

Materialized VIEWs 257 In-line VIEWs 259

Updatable and Read-Only VIEWs 2 6 1 View Column List 263

WITH CHECK OPTION Clause 263 Dropping Views 265 Hints on Using VIEWs 266

The CREATE SCHEMA Statement 266 Summary 266

Chapter 11 : Embedded SQL 269

Where Are We Now? 270 Embedded SQL 270

Problems of using SQL in a Procedural Host Language 271 How Embedded SQL Operates 271

SQLDA 272 SQLCA 273

Declarations 273 CURSORS 275

The DECLARE CURSOR Statement 275 The OPEN CURSOR Statement 277 The FETCH Statement 277 The CLOSE CURSOR Statement 278 The Single Row SELECT Statement 278 Update and Delete by Position on Updatable Cursors 279 The Positioned DELETE Statement 279 The Positioned UPDATE Statement 280

An Example of C-Embedded SQL 2 8 1 Summary 286

Chapter 12: Optimization and Performance Tips 289

The SQL Database Engine 290 Database Schemas 290

The Optimizer 292 Queries 292 The lnformation_schema Tables 292

Database Access Methods 293 Indexing a Table 293

Keys and Indexes 294 Index Defining 294 An Example of Indexing 294 Clustered Indexes 295 Other Index Options 295 Binary Tree Indexing 296 Indexing Techniques 297

Hashing 297

Hints on How to Write Queries 299 Understanding the Question 299

Table of Contents

Fill in the Select List First 300 Put Table Names in the From Clause 3 0 1 Joining Tables Together 302 Group the Table 303 Design the Having Clause 303

Back up and Decompose the Problem into Simpler Parts 304 Put the Simpler Parts Together 304

Repeat the Process Iteratively and Recursively 306 Test and Repair your Query 307

B a g of Tr icks 3 0 9

Summary 3 1 0

Where Do We Go From Here? 313

Appendix A: Conversion Notes for Different Vendor SQLs 315

Oracle 316 Chapter 2 : Table Creation 316 Chapter 2 : General Implementation Notes 317 Chapter 3 : General Implementation Notes 317 Chapter 4 : Code Details 317 Chapter 4 : General Implementation Notes 319 Chapter 6 : General Implementation Notes 319 Chapter 7 : General Implementation Notes 319 Chapter 8 : General Implementation Notes 320 Chapter 9 : General Implementation Notes 320 Chapter 10 : General Implementation Notes 321

Sybase 321 Initialization 321 Chapter 2 : Code Details 322 Chapter 2 : General Implementation Notes 323 Chapter 3 : General Implementation Notes 324 Chapter 4 : Code Details 325 Chapter 4 : General Implementation Notes 326 Chapter 5 : General Implementation Notes 327 Chapter 6 : General Implementation Notes 327 Chapter 7 : General Implementation Notes 328 Chapter 9 : General Implementation Notes 328 Chapter 10 : General Implementation Notes 329 Chapter 12 : General Implementation Notes 329

Access 330 Chapter 2 : Code Details 331 Chapter 2 : General Implementation Notes 331 Chapter 3 : General Implementation Notes 332 Chapter 4 : Code Details 332 Chapter 4 : General Implementation Notes 333 Chapter 6 : General Implementation Notes 333

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Chapter 7 : General Implementation Notes 334 Chapter 8 : General Implementation Notes 335 Chapter 9 : General Implementation Notes 335 Chapter 10 : General Implementation Notes 336 Chapter 11 : General Implementation Notes 337

Appendix B: Example Databases 339

How to Create the Example Database 339 Inserting the Data 340

Chapter 6 Examples 355 The Foobar Table 355

Creating the Table 355 Inserting the Data 356

The Foo Table 356 The Bar Table 356

Appendix C: Security and Control in Your Database 359

Privileges and Security 359 The GRANT Statement in Watcom SQL 360

Users 360 Granting Privileges 3 6 1

Grantors and Grantees 361 The PUBLIC Grantee 362

Schema Objects 362 Privileges 362

Actions 363 Example Usage of the GRANT Statement 364 The REVOKE Statement 365 Example Usage of the REVOKE Statement 366 Summary 366

Appendix D: Standards and Quasi-standards

Groups Involved with SQL 369

Appendix E: Table of Legal Conversions 373

Index 377