Appendix A. Relational Database Technology: A Crash Course

ADO.NET can be used to access data from any data source: relational databases, object databases, flat files, and text files. The vast majority of web applications, however, will access data from a relational database such as SQL Server. While one can certainly write an entire book on relational databases and another on SQL, the essentials of these technologies are not hard to understand.

All of the examples in this appendix assume you are working with SQL Server and that the flavor of SQL you are using is T-SQL. Users of other relational databases will find that the lessons learned here transfer well to their environment, but be especially careful with applications like Access that use a different variation of SQL.

A database is a repository of data. A relational database organizes your data into tables that are "related" to one another. For example, one table might contain a customer's information and a second table might contain information about orders. The tables are related to one another because each customer has certain orders, and each order is owned by an individual customer.

Similarly, you might have a table of cars and a second table of car parts. Each part can be in one or more cars, and each car is made up of parts. Or, you might have a table for bugs and a table for developers. Each bug is owned by one developer, and each developer has a list of bugs he owns.