Informix Guide to SQL Tutorial
The Informix Guide to SQL: Tutorial includes instructions for using basic and advanced Structured Query Language (SQL) as well as for designing and managing your database. This manual is part of a series of manuals that discusses the Informix implementation of SQL. Once you finish reading this manual, you can use the Informix Guide to SQL: Reference and the Informix Guide to SQL: Syntax as references to help you with daily SQL issues.
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This book is about databases and about how you ca- exploit them using Informix software. As you start reading, keep i- mind the following fundamental database characteristics: a database comprises not only data but also a plan, or model, of the data; a database ca- be a commo- resource, used concurrently by many people. Your real use of a database begins with the SELECT statement, which is described i- Chapter 2, “Composing Simple SELECT Statements.”
This chapter covers the fundamental concepts of databases and defines some terms that are used throughout the book, emphasizing the following topics:
- What terms are used to describe the mai- components of a database?
- What language is used to create, query, and modify a database?
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The Data Illustration of a Data Model
The principal difference between information collected in a database versus information collected in a file is the way the data is organized. A flat file is organized physically; certain items precede or follow other items. But the contents of a database are organized according to a data model. A data model is a plan, or map, that defines the units of data and specifies how each unit is related to the others. For example, a number can appear in either a file or a database. In a file, it is simply a number that occurs at a certain point in the file. A number in a database, however, has a role that the data model assigns to it. It might be a price that is associated with a product that was sold as one item of an order that was placed by a customer. Each of these components, price, product, item, order, and customer, also has a role that the data model specifies
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Tags: database administrator, database connection, database management, database schema, database server, database tables, Informix, informix database, SQL, SQL Query
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