I call BS if they "take points off" for not knowing the exact term "joint table", and if so that's not the kind of company I'd want to work for.
Sadly, looking for excuses to rationalised that the interviewer doesn't like you is still a thing.
Edit: On the other hand, asking the question in a way that gets at the concept, not the term, seems very reasonable.
I don't think it's relevant, but yes, I have interviewed at such companies.
I don't believe OP is aware of the existence of table joins, and just reproduced what he thought was mentioned.
Meanwhile, the DB operation he described is clearly a table join (create a new table by creating a relationship between two existing tables).
That is also quite clearly a good reason for a prospective employer to lose interest in OP as a potential recruiter, and why his projects on Github fail to impress anyone. Portfolio projects only work in favor of a job applicant if they are any good, but if they are all a bunch of crap that is poorly put together and showcases incompetence, such as setting up a database system that tries to reinvent the wheel to fill in the gap of not knowing the very basics, then obviously that is disheartening to any potential recruiter.
I don't think this is an SQL concept. The only people I've heard use this word (phrase?) are people who work with Java ORMs.
It's really hard to even recall dozens of these experience and shrink them into stories and putting words to these. In the startup world, it's called 'Get Shit Done'. In the monolithic FAANG & FAANG wannabe world, I dunno what it's called...
Maybe if everyone replies if they have heard it or not we can reach a conclusion if it is a known term in Hacker News community.
Or we can decide that such anecdotes are of little value to the discussion and stop posting them since it is unrealistic to reach the above mentioned conclusion just by reading them and it can mislead some readers.
That's a major problem. Table joins are the most basic concept in relational databases. A so called developer who puts together a database but isn't even aware of table joins is someone who didn't even browsed through a basic SQL tutorial and is completely oblivious to concepts such as database normalization.
To put it in perspective, it's like claiming you are a proficient developer but are oblivious to the use of if statements.
If you're really interested in software development and web services I'd suggest you invest a couple of hours learning the basics of relational databases, including a brief intro to normalization. That is mandatory if you want to avoid more accusations of incompetence.