I'm thinking that the book I learned Pascal from back in 1981 used a similar notation (if not identical) for showing syntax. Of course with nearly 30 years intervening, I can't come up with the name of the book, let alone the book itself nor can I be 100% certain that I remember what the syntax diagrams looked like.

FYI The syntax duagram is called a railroad diagram, and is particularly common in RDBMS docs (probably because SQL syntax is basically nonsense)

It's quite amazing that all these years on, SQL is still king. There are basically no rules for the syntax, how come nothing cleaner replaced it in RDBMSes?

Two things I think: it ultimately doesn't matter, because the key differentiator between RDBMS selection is the management system, not the query system

And second is that RDBMS's are historically closed-source enterprise tooling -- the vendors themselves have little interest rocking the boat, and there's not much freedom for the community to inject a new language into the system (except as ad-hoc, wonky transpilers, or framework wrappers like ORMs)

It would be better if the images weren't a billion pixels tall so you could actually read them.