If you want to learn SQL you can find a lot of useful tutorials online. One of the best things about SQL is that it is portable across a variety of database platforms and programming languages, with a few vendor specific differences here and there. Oracle SQL might be slightly different than SQL Server SQL but they are mostly the same.
One thing I would recommend for anyone wanting to really grasp Structured English Query Language is to learn database normalization concepts such as first normal form, second normal form and so forth. These concepts will show you how to break up your data in chunks that can then be related to one another, and then the concepts behind a SQL join statement will become easy to understand.