When it comes to relational databases, I can’t help thinking that something is missing. They’re used everywhere. There are many different databases: from the small and useful SQLite to the powerful Teradata. But, there are only a few articles that explain how a database works. You can google by yourself “how does a relational database work” to see how few results there are. Moreover, those articles are short. Now, if you look for the last trendy technologies (Big Data, NoSQL or JavaScript), you’ll find more in-depth articles explaining how they work.

Are relational databases too old and too boring to be explained outside of university courses, research papers and books?

As a developer, I HATE using something I don’t understand. And, if databases have been used for 40 years, there must be a reason. Over the years, I’ve spent hundreds of hours to really understand these weird black boxes I use every day. Relational Databasesare very interesting because they’re based on useful and reusable concepts. If understanding a database interests you but you’ve never had the time or the will to dig into this wide subject, you should like this article.

Though the title of this article is explicit, the aim of this article is NOT to understand how to use a database. Therefore, you should already know how to write a simple join query and basic CRUD queries; otherwise you might not understand this article. This is the only thing you need to know, I’ll explain everything else.

I’ll start with some computer science stuff like time complexity. I know that some of you hate this concept but, without it, you can’t understand the cleverness inside a database. Since it’s a huge topic, I’ll focus on what I think is essential: the way a database handles an SQL query. I’ll only present the basic concepts behind a database so that at the end of the article you’ll have a good idea of what’s happening under the hood.

Since it’s a long and technical article that involves many algorithms and data structures, take your time to read it. Some concepts are more difficult to understand; you can skip them and still get the overall idea.

For the more knowledgeable of you, this article is more or less divided into 3 parts:

• An overview of low-level and high-level database components
• An overview of the query optimization process
• An overview of the transaction and buffer pool management