The GROUP BY Clause
by Sandra L. Emerson, Marcy Darnovsky, Judith S. Bowman
Practical SQL Handbook, The: Using SQL Variants, Fourth Edition
- Copyright
- List of Figures
- Foreword to the Fourth Edition
- Preface
- Introduction
- SQL and Relational Database Management
- Designing Databases
- Creating and Filling a Database
- Selecting Data from the Database
- Sorting Data and Other Selection Techniques
- Grouping Data and Reporting from It
- Joining Tables for Comprehensive Data Analysis
- Structuring Queries with Subqueries
- What Is a Subquery?
- How Do Subqueries Work?
- Joins or Subqueries?
- Subquery Rules
- Subqueries Returning Zero or More Values
- Subqueries Returning a Single Value
- Subqueries Testing Existence
- Subqueries in Multiple Levels of Nesting
- Subqueries in UPDATE, DELETE, and INSERT Statements
- Subqueries in FROM and SELECT Clauses
- Summary
- Creating and Using Views
- Security, Transactions, Performance, and Integrity
- Solving Business Problems
- Syntax Summary for the SQL Used in This Book
- Industry SQL Equivalents
- Glossary
- The bookbiz Sample Database
- Resources
- CD ROM Warranty
- Using the Practical SQL Handbook CD
The GROUP BY Clause
The GROUP BY clause is intimately connected to aggregates. In fact, GROUP BY doesn't really have much use without aggregate functions: it divides a table into sets of rows, and aggregate functions produce summary values for each set. These values are called vector aggregates. (A scalar aggregate is a single value produced by an aggregate function as discussed in the previous chapter.) Figure 6.1 shows examples of scalar and vector aggregate queries.
Figure 6.1. Scalar and Vector Aggregates
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