Remember to Read the Manual!
There are few areas in computing more shrouded in mystery than databases! This reminds me of the way some programmers used to refer to themselves as GUI specialists. It's probably a bit dangerous to pigeonhole yourself in this way; a better approach is to try to get a solid appreciation of more than one area. Learning about database technology is probably one of the soundest investments you can make because it is an increasingly ubiquitous technology; it's even now available in browser-based applications.
One of the many things I like about Derby is the combination of code examples and excellent documentation. It's no longer necessary to read countless manuals to get a simple application working. You can now do it on your own just by reading a little.
As you dig deeper into Derby, you'll probably notice that database technology is often a little weird, an example of which is the CLOB (character large object) entity. CLOBs can be used when you want to store a block of text data in a database table. So, in a sense, a CLOB is a type of array. A CLOB can be up to 2,147,483,647 characters long and is used to store Unicode character-based data, such as large documents in any character set. From a programmer's standpoint, CLOBs are a little odd in that they're indexed from 1 rather than 0. The database world requires something of a change in mindset!
I always find there's nothing quite like knowing what you're talking about! So I strongly recommend reading the Derby documentation. It's packed with examples and explanations of database technology elements. It's likely that database applications will be squeezed into the smallest of devices, so a sound knowledge of Derby will most likely serve you well.