Relational Databases

Originally defined by E. F. Codd, relational databases store data in tables, made up of columns and rows. For example, the following table could be used to store customer information:

Figure 7.1: A database table of customers

In this customer table example, each row has four columns: an ID, a username, a first name, and a last name.

Note

In addition to celebrities such as Sting, Cher, and Bono, some ethnic groups use just one name. You will not always have first and last names.

Each row needs a unique way to distinguish that row from all others, called a unique primary key. In this case, the ID column acts as a unique key. In this table, you could also use the username as a unique key.

Some tables use a single column as a key, while others use the values in multiple columns to form the key, called a composite key.

Most databases use more than one table. You can relate tables to other tables based on information within a row...