RelationalDBDesignRelationalDBDesign





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Lesson 9

SQL works with the information in your Database Systems

In the coming modules, you will quickly begin to understand how SQL works with the information in your systems and how it can be applied to satellite television.
SQL was designed for relational database systems, thanks to Dr. Edgar Codd.

You will find out how relational approaches differ from more traditional databases, and why this is important to understand as you start using SQL.
Finally, you will learn about normalization. Understanding normalization is key to using databases, and the concepts are straightforward yet powerful. By obtaining a good understanding of the ideology now, you will be set not only to query databases but to understand the underlying reasoning behind setting them up in the manner in which they were created.

Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy and dependency.
Normalization usually involves dividing large tables into smaller (and less redundant) tables and defining relationships between them. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database using the defined relationships.



The SQL standard has gone through a number of revisions:

Well Know RDBMS using SQL

4e Dimension (4D) Microsoft Access Adonix X3 OpenOffice Base
DB2 (AS400) Firebird Visual FoxPro HyperFileSQL
Informix Ingres MariaDB MaxDB (anciennement SAP db)
Microsoft SQL Server Mimer MySQL
Ocelot Oracle Paradox PostgreSQL
SQLite SQL/MM Sybase Teradata
Microsoft Excel HSQLDB CUBRID

All these systems have some particularities, and some of these oddities are not found in others. Moreover, it is always interesting to refer to the reference manual RDBMS during special or complex queries, as well as their optimization.
SQL is a standard language for accessing databases. This SQL tutorial will teach you how to use SQL to access and manipulate data in: MySQL, SQL Server, Access, Oracle, Sybase, DB2, and other database systems. With our online SQL editor, you can edit the SQL statements, and click on a button to view the result.
Example:
 SELECT * FROM Customers;