Just relax and be yourself. Pretend you've known the people that are interviewing you for a thousand years. There's nothing else you can do to prepare yourself because there's no way to predict what they're going to ask you about SQL Server and databases. Either you know the stuff... or you don't. It may help you if you start the interview with an admission that it's your first ever interview for such a position and that you're about to pass the proverbial brick.
Depending on how you've written it, I might not be able to help you with this current interview but it may help on the next one. The one thing I can predict they'll ask you about is your resume, especially if you've made any claims of experience there. If you've lied on your resume or have falsely embellished any experience or perceived skill, expect that to be your ultimate demise because they WILL find out during the interview.
What else might they grill you on? Even if I gave you a list of the exact questions they might ask, if you don't know the answers already, then no amount of cramming is going to help you because your answer will be canned answers from a book or a blog and not from experience.
Even if you don't "pass" this first interview, use it as a super learning experience. Except for the questions asked and the attitudes of the people conducting the interviews, they're all pretty much the same. Learn to use that to your advantage.
If you have some nicely formatted documented code that you're proud of, take several printed copies with you and ask them if they'd like to see an example of your work. Make sure that it's not a copy job from somewhere on the internet. Make sure that it's your own work. Trust me... they'll be able to tell. But, they'll also be incredibly impressed that you were thoughtful enough to prep for the interview.
Also be very aware of what the company actually does. Do your research. People really like it a lot and may pick someone less qualified than others if they show such a keen interest in the company they're applying to for a job.