Can you do the job? Do you want to do the job? Don't try to be something your not. It's really tempting to try and fit your skills into what the client is looking for because you need the money. Don't do that. In the end, if the client is not happy, it could hurt your reputation and future business leads.
Find out if they are talking to other vendors and if so, what criteria they will use to select one for the project. Be aware of how your potential client sees you. Put yourself in your client's shoes and ask yourself if you would hire you.
If you decide your skills aren't the best for this project, be honest and tell the client the your expertise is not in the area they need. Refer them to someone who might help them. Ask them for referrals of potential clients that are looking for database development with your area of expertise.