在C＃中，如何使用SQL检查数据库中的现有数据？

I'm working in c# and using sql commands to get, add, change data in a Access db. What I would like to do is check a table in the db for specific data, or record. I would need the command to return a value (true/false, 0/1) that will indicate if the data exist or not. My overall goal is to be able to run this check and if the data exist, then do nothing. If the data doesn't exist, then create it. Does anyone know how to do this. I assume there is a way to do this with sql, but I could be wrong. That's about it. I hope I presented my problem and question properly.I'm working in c# and using sql commands to get