Check if value exists in Access Database using c#

I wish to enter data into my access database table like so:

private OleDbConnection mycon;
string sDBPath = Application.StartupPath;
string sConnection = string.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0}\\MyAccessDB.mdb;Persist Security Info=False", sDBPath);

mycon = new OleDbConnection(sConnection);
OleDbCommand cmd = mycon.CreateCommand();
   cmd.CommandText = "insert into MyTable values('" + sID + "','" + sData1+ "','" + sData2+ "','" + sData3+ "','" + sData4+ "');";

cmd.ExecuteNonQuery();
 mycon.Close();

My question is how do I check if an entry already exists in the database row.  e.g. the first variable sID above?

Thanks