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SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL, Second Edition by Michael J. Hernandez, John L. Viescas

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Anatomy of a Relational Database

According to the relational model, data in a relational database is stored in relations, which are perceived by the user as tables. Each relation is composed of tuples (records) and attributes (fields). A relational database has several other characteristics, which are discussed in this section.

Tables

Tables are the main structures in the database. Each table always represents a single, specific subject. The logical order of records and fields within a table is of absolutely no importance. Every table contains at least one field—known as a primary key—that uniquely identifies each of its records. (In Figure 1-1, for example, CustomerID is the primary key of the Customers table.) In fact, data in a relational ...

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