XPathNavigator field3 =
            this.MainDataSource.CreateNavigator().SelectSingleNode(
             "/my:meineFelder/my:feld3", NamespaceManager);

XPathNavigator field1 =
            this.MainDataSource.CreateNavigator().SelectSingleNode(
             "/my:meineFelder/my:feld1", NamespaceManager);
            field3.SetValue(field1.Value);

                        AdoQueryConnection connection = (AdoQueryConnection)this.DataConnections["Bezeichnung"];
                        string orgCommand = connection.Command; //To read original command   
                        connection.Command = "select \"artbez\",\"vk_preis\" from \"dbo\".\"f01\" as \"f01\"" +
                                             " where \"artikel_nr\" = '" + field28.Value + "'";
                        connection.Execute();
                        connection.Command = orgCommand;