Comment by perrygeo

Learn SQL (because it's basically the only option) but much more importantly, learn databases. Know why atomicity, consistency, idempotency, and durability matter. Understand the wire protocol and the client-server model. Do relational data modeling; think beyond databases as a dumb store. Join. Know when to normalize. Internalize indexing strategies. Think deeply about what work belongs on the database server (work that can leverage relational set theory) and what work stays in the application. Once you figure the true capabilities of databases, SQL as the language interface is a side note - about as important as the leather on your steering wheel.