string connectionString = String.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};", _local_dbname);
OleDbConnection connection = new OleDbConnection(connectionString);
try
{
    connection.Open();
    OleDbCommand command = new OleDbCommand("SELECT * FROM myTable where key = from your variable/memory", connection);
    OleDbDataReader reader = command.ExecuteReader();
    while (reader.Read())
    {
        Console.WriteLine("reading row: "  + reader["ID"].ToString());
    }
    reader.Close();
}
catch (Exception ex)
{
    // your exception

}