I recently asked my 4th-year students (who take a relational database course in their 3rd year) how much they used what they learned from the database course. Most of them had internships between the 3rd and 4th year, and they told me that in their jobs they needed to (a) write complex queries and (b) write stored procedures. Our database course had focused, I think, too much on ER diagramming and things like field data types. You need to know those things to create a database, but as a new person I guess you're more likely to have to deal with a database that already exists.

To my point: make sure you learn how to do complex SQL queries including subqueries and correlated subqueries. Also, learn to create stored procedures and triggers in your favorite database.

You might look into the book "Refactoring Databases" by Ambler and Sadalage. It challenges you to think about the database as an evolving system, which is different than the kind of textbook exercises where you just sketch or build it once and then move on to the next problem.