[kephra]

Old but classic is C.J.Date's "An Introduction to Database Systems". This book covers most concepts required for databases, and the reason why relational databases had been an improvement over prior key-value, hierarchical, and network databases.

One could consider relational language as a database kernel language.

[bordercases]

OK, I thought relational modelling was more niche than that, thanks. But as long as we're on the topic of the kernel language model, I'm getting reminded of the fact that every time we add a stratification to the KL, we don't get a _better_ language; instead we get a _different_ language, with its own set of strengths of weaknesses.

For example, if the relational language is the database kernel language (model?), why does the "degradation" towards key-value pairs benefit a cache like Redis?

I'm all for principles books on databases right now, so thanks, I'll take a look.

EDIT: oh, CJ Date wrote "Database in Depth: Relational Theory for Practitioners", which seems newer. Do you know how they compare?

[pjungwir]

I just finished Database in Depth. :-) It is short and readable. It's targeted to working database programmers with a few years of SQL already. I learned a bit, but it was a bit of a bait-and-switch: the book is really a polemic about why SQL is not relational enough and people should use the author's own Tutorial D. Every page belabors that point. More examples are written in Tutorial D than SQL. I was hoping for some math & theory, and there was some theory, but there was little effort to connect it to SQL except to show SQL's shortcomings. For instance I never once saw the term "outer join" (because Date wants to forbid NULLs). If you are interested in database theory and trying new things, it might be very interesting. If you are a working programmer who wants to solidify the foundations, there are probably better choices (I hope).