You could learn how to design a database properly by trial and error, but it would take you a very long time, and you would probably have to repair many mistakes along the way. The best approach is to learn a good database-design methodology, such as the one in this book, and then embark on designing your database.
You'll gain several advantages from learning and using a good design methodology.
It gives you the skills you need to design a sound database structure. A large number of data-processing problems can be attributed to the presence of redundant data, duplicate data, and invalid data, or the absence of required data. All of these problems produce erroneous information and make certain queries and reports difficult to run. You can avoid almost all of these problems by employing a good design methodology.
It provides you with an organized set of techniques that will guide you step-by-step through the design process. The organization of the techniques enables you to make informed decisions on every aspect of your design.
It helps you keep your missteps and design reiterations to a minimum. Of course, you will naturally make some mistakes when you're designing a database, but a good methodology helps you recognize errors in your design and gives you the tools to correct them. Additionally, the organization of the techniques within the methodology keeps you from unnecessarily repeating a given design process.
It makes the design process easier and reduces the amount of time you spend designing the database. You will inevitably waste valuable time taking an arbitrary trial-and-error approach to design because it lacks the logic and organization that a good methodology provides.
It will help you understand and use your RDBMS software more fully and effectively. As your knowledge of proper design expands and grows, you'll actually begin to understand why a given RDBMS provides certain tools and how you can use them to implement the structure within the RDBMS program.
Regardless of whether you use the design methodology presented in this book or some other established methodology, you should choose a design methodology, learn it as well as you can, and use it faithfully to design your databases.