“How does a relational database work” is an excellent (lengthy, technical, but simply written and well explained) article on some of the most important bits inside the relational database. It’s somewhat of a middle ground between a theoretical database discussion in college and vendor-specific documentation of a database engine.
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.
Whether you are a young programmer or an experienced DBA, I think, you’ll still find something in there which you either didn’t know or didn’t think about in this particular way. Even if you know all this stuff, it’s a good memory refresher.