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Beginning SQL Queries - From Novice to Professional
of: Clare Churcher
Apress, 2008
ISBN: 9781430205500 , 240 Pages
Format: PDF, Read online
Copy protection: DRM
Contents at a Glance
5
Contents
6
About the Author
12
About the Technical Reviewer
13
Acknowledgments
14
Introduction
15
Relational Database Overview
17
What Is a Relational Database?
17
Retrieving Information from a Database
26
Summary
31
Simple Queries on One Table
32
Retrieving a Subset of Rows
35
Retrieving a Subset of Columns
37
Using Aliases
38
Combining Subsets of Rows and Columns
39
Saving Queries
40
Specifying Conditions for Selecting Rows
40
Dealing with Nulls
44
Managing Duplicates
47
Ordering Output
50
Performing Simple Counts
50
Avoiding Common Mistakes
51
Summary
54
A First Look at Joins
56
Joins in Relational Algebra
56
Joins in Relational Calculus
60
Extending Join Queries
61
Other Types of Joins
69
Summary
73
Nested Queries
75
IN Keyword
75
Using IN with a Nested Query
76
Being Careful with NOT and <>
78
EXISTS Keyword
81
Different Types of Nesting
83
Using Nested Queries for Updating
87
Summary
89
Self Joins
90
Self Relationships
90
Questions Involving “ Both”
101
Summary
105
More Than One Relationship Between Tables
107
Representing Multiple Relationships Between Tables
107
Algebra Approach to Two Relationships Between Tables
109
Calculus Approach to Two Relationships Between Tables
113
Business Rules
114
Summary
117
Set Operations
118
Overview of Basic Set Operations
119
Union- Compatible Tables
120
Union
122
Intersection
128
Difference
134
Division
138
Summary
143
Aggregate Operations
144
Simple Aggregates
144
Grouping
150
Nested Queries and Aggregates
158
Summary
161
Efficiency Considerations
163
Indexes
163
Query Optimizer
171
Summary
177
How to Approach a Query
178
Understanding the Data
178
Big Picture Approach
183
Spotting Key Words in Questions
188
No Idea Where to Start?
192
Checking Queries
195
Summary
197
Common Problems
199
Poor Database Design
199
Problems with Data Values
205
Diagnosing Problems
208
Common Symptoms
210
Common Typos and Syntax Problems
215
Summary
216
Sample Database
217
Index
219
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