Chapter 2. Database Design Essentials

A relational database is essentially just a set of tables of data that are related to each other. These tables are useful because we can use a high-level language, such as SQL, to add, change, or delete the tables or the data in the tables. We can query the database and obtain the results of selecting data based on simple or complex relations. We can perform set operations, such as joins, on the data. These capabilities let us store, manage, and make use of even very large amounts of data.

Tables can hold data of different types, allowing us to store, primarily, numbers, dates, and text. We can perform calculations, sort, or change these types of data. (There are also types used to store arbitrary data which could be images or sounds, for example but they are just "stuff" to the database and we cannot perform operations on these types apart from storing it and retrieving it. These cannot be manipulated using SQL and won't be considered until Chapter 9, "Advance JDBC Features.") The Oracle SQL datatypes correspond only roughly to Java types and mapping from one to the other requires some care.

Designing a database is largely a matter of determining the types of data in each table and determining the relationships between each of the tables in the database. Exploring a little of the theory behind relational database design will prevent problems such as redundant data or a database that is difficult to use.