"Depends on what you mean by "trivial". "
Anything that has more than say, 2 tables, is what I meant by "non trivial" ;-)
"Sites like this aren't exactly heavy on the SQL."
Invalid refutation, I said "if you used an RDBMS and ". That "and" was a boolean and.
I never said you had to use an RDBMS to make a useful website. But if I was hiring for an RDBMS backed website , and you claimed to have used an RDBMS "for years" you'd better damned well know the basics. No "I don't know how to do a join across two tables because I did it in the application layer" doesn't cut it. That is a really stupid explanation of your ignorance and blows a big hole in your supposed "experience" with RDBMS.
"You don't have to drop below it; you can go "above" it into the application layer."
Sure you don't have to drop below the ORM. But you'd better know how to and when to . I wouldn't trust a developer with an ORM who didn't know ultra basic SQL. And a join in an RDBMS is ultra basic - someone claiming knowledge of an RDBMS and not knowing how to do a simple join across two tables (the OP's question was aa simple join across two tables) is like someone claiming to be an expert in c and not knowing how to write a for loop (let alone use pointers). Is that possible? I guess, Is it probable? Not at all.
Besides, using an ORM and doing a join in the application layer (without knowing how to do a SQL join) is ... unusual ;-).
"Let's consider the case of someone with a PhD who ISN'T famous, and then you give him some kind of SQL test and he fails. "Man, what a load of bullcrap his PhD is! He can't even do a simple JOIN!""
Well if the PhD applied for a job that needs SQL he'd better know how to use SQL (or learn - it would take what, one day of reading a basic book on SQL to understand what a join is and formulate a query? If the PhD couldn't do that and claimed he had lots of experience with RDBMS and then said he didn't know how to write a join, then I'd write him off as incompetent (and possibly a liar) for this job, irrespective of his degree, sure) .
" A lot of them don't write joins."
as long as they can write a join after claiming to have worked with RDBMS for ages ;-)
"So, once again, the danger of using any litmus test is you can end up filtering out extremely capable people who don't do X (but could obviously pick it up quickly), while passing minimally-capable people who CAN do X."'
The danger of NOT using a quick and easy litmus test is that all kinds of idiots get through to your personal interview stage and you end up wasting a lot of time talking to incompetent people.