public class DbHelper
{
    static DbHelper()
    {
        connectionString = GetConnectionString();
    }

    private static string connectionString;

    private static string GetConnectionString()
    {
        return string.Format( "File Name={0}\\link.udl", Application .StartupPath);
    }


    public static DataTable ExecuteDataTable( string sql)
    {
        try
        {
            using ( OleDbDataAdapter da = new OleDbDataAdapter (sql, connectionString))
            {
                DataSet ds = new DataSet();
                da.Fill(ds);
                return ds.Tables[0];
            }
        }
        catch( Exception e)
        {
            MessageBox.Show(e.Message);
            return null;
        }

    }

    public static void ExecuteNonQuery( string sql)
    {
        using ( OleDbConnection conn = new OleDbConnection (connectionString))
        {
            try
            {
                conn.Open();

                OleDbCommand cmd = conn.CreateCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = sql;
                cmd.ExecuteNonQuery();
                cmd.Dispose();
            }
            finally
            {
                if (conn.State == ConnectionState.Open) conn.Close();
            }
        }          
    }

}