I honestly don't grasp why this is a good question.

Sure, I write a SQL query now and again, but if I have to join I look it up. I don't do it a lot. If I had to do it a lot for you, I would learn it inside out.

If I told you I was a DB wizard, then sure, I better already know how to join. But I know tons of people that don't really do SQL. They are eminently hire-able and valuable.

source: a guy (me) who was bounced out of an interview because he didn't recall some specific detail about boost::shared_pointer().