Ask HN: Refresher course on (My)SQL?

Hello, everyone. I am a university student who recently got a part-time job working as a Web developer at the university's IT department, starting shortly after I return from Christmas break. It's a PHP and MySQL job, and while those aren't my favorite tools (Python + Postgres/Redis FTW), it's programming and on-campus, and I have done some non-database PHP stuff recently.

Problem is, all the database stuff I have done recently has been with ORMs or with non-SQL databases entirely. As such, my grasp of written SQL has declined greatly and I could use a refresher course. Are there any books or tutorials on SQL (especially MySQL) that you would recommend for someone who has database and Web programming experience but doesn't know much written SQL?