Relational Database

BAs must understand the terms tables, rows, columns, and keys in the relational database

A relational database is a place to store data. Almost every piece of information that is important to an organization is stored in a relational database. It is really amazing that this one approach to storing information has been universally accepted and maintained. Although it is not important that a BA understand the underlying details for its universal success, it is based on a solid mathematical model that has stood and will stand the test of time. In other words, there are very good reasons why everyone uses it! It is a fundamentally sound approach to organizing and understanding data requirements.

The good news about this method of storing data is that at a high level it is relatively easy to understand. Data is stored in tables. If you have used a spreadsheet with rows and columns, then you understand the basic structure of a relational database table. See Table 5.2 for an example. Each column represents a data element and each row contains the data values for each data element. This simple structure is used to store and report on very large and complex types of information.

Table 5.2: Sample Relational Database Table
Customer Table
Customer Number	Name	Phone	E-mail Address
103	Smith	383-3839	smith@yahoo.com
104	Jones	495-0059	jones@hotmail.com
105	Carkenord	232-2020	bcarkenord@b2ttraining.com

Table 5.3: Sample Relational Database for Customer Related to Order

Every table has a primary key. A primary key uniquely identifies a particular row in the table. In the sample customer table in Table 5.2, the customer number is the primary key. A primary key is made up of one or more columns.

Database complexity is introduced by the relationships between the tables. Tables are related to each other via foreign keys. A foreign key is a primary key from the related table. Take the time to learn the basics of foreign key migration because these relationships between tables are critical for accessing data. Table 5.3 shows two related tables. Note that the customer number column exists in the order table as a foreign key. You can learn about relational databases by reading a book like the Handbook of Relational Database Design (Fleming and von Halle, 1989).

Deciding which pieces of information should reside in each table and how many tables are appropriate is the work of a database designer or architect (see Chapter 2).