Learn the Basics of RBD and SQL

Hi. Since I have just finished my degree in CS I was looking for my first job. Now my biggest concern is my poor knowledge about the SQL and Relational Databases. I am looking for good and concrete courses fast to read but difficult to understand. The level of the courses I am looking for are the same as the papers: "A relational model of data for large shared data banks" and "The entity relationship model". The roots of RDB.

Could you help me?