Here's the thing to remember when working any job:
You do the work the company needs you to do.
You may not feel that database and server support are worthy of your time. Unfortunately, the only two words to describe the situation are tough luck. I'm not trying to be mean, it's just the way it is.
What an employee is to a company is basically a solution to a problem.
If their problem is that they need new code written, they will hire someone to fill that role.
If they need bugs fixed, they will fill that role.
If they need a database maintained, they will fill that role.
The problem arises when the issues they need fixed do not align with your professional aspirations and interests. When this happens you have to decide whether continuing with that company is worth your time - and many considerations must be weighed in order to reach the correct decision, each particular to you.
So here's some things to keep in mind, and ask yourself:
If you were to start coding new software solutions for this company would the technologies, process, and techniques employed interest you? Would you be learning new things, and growing professionally? Would that turn of events satisfy you?
If your answer is no, then there's no point working there any longer - start applying for a new job.
If however, your answer is yes, then staying with this company is potentially beneficial if you stick with it. Sure, they have you doing database/server maintenance right now, but a couple of months down the road you may transition back to development. You'll need to find out what their plans are for you, or even if they have a plan. A conversation with your boss will be required:
Hey, boss. I wanted to talk to you about your plans for me within the company. I know the server and database maintenance is critical to the company's success, and I've been happy to do it, however I wanted to raise some concerns. While I've been able to handle my new responsibilities so far, I have to tell you that my expertise does not lie in the area of network admin. I can hum the tune, and I think I've been doing alright, but I'm not an expert. A situation may easily arise that I don't know how to handle, or worse, I don't handle correctly. I honestly think it would be in the company's best interest to hire a network admin with the correct experience to manage our servers. Furthermore, I don't feel that this experience is allowing me to grow professionally - I'm trained as a developer, not a system admin. It's always good to pick up some new skills in a related field, but it's not my area of professional interest. What are your thoughts on this situation?
That was a little long winded, but it will hopefully spark a meaningful conversation about what role your boss envisions for you within the organization. If he has no vision, then your alarm bells can start ringing: the company is simply putting out the latest fire, and has no medium or long term plan on how to deal with the issue. It might be a long time before they hire a proper system admin, and you must decide whether you want to be stuck in that role for the foreseeable future or not.
Your company needs you to fill the role of a system admin, but are they willing to allow you to also gain experience in your area of interest?
Even if your boss can't transition you out of the admin role, he may be able to allow you to do some development, and thus polish your skills, and learn new things. That might make the job worth it, especially if it's a good work environment / a decent paycheque / you have good benefits.
At the end of the day you're the one who knows your situation best. I highly recommend having that conversation with your boss. Remember to always be polite, and not to display frustration! Simply be honest and earnest, as if you're really doing the company a favor by pointing out that you're not a system admin.