It's funny but I think I learned about relational database theory (normal forms and such) from the early chapters and/or appendices of thick computer books written about products like Delphi, FoxPro, and MS Access. The data-modeling knowledge scaled up really well to stand alone database servers of various kinds! It's too bad there isn't something similar for new learners, some in-the-browser environment they could enter to try out their nascent SQL skillz. Ideally something with a big thick paper book, too! (The book is a shibboleth representing stability of API and seriousness of purpose, which are too-rare qualities in today's software products.)