This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
SCJA is an entry-level certification. It shows that you understand the basics of what Java is, but it doesn't test if you can write programs in Java. If you're a programmer, then SCJA is most likely not very useful. You don't need to be SCJA-certified to do SCJP.
SCJP is the Java certification for programmers. With this, you show that you know how to program in Java.