Javascript SQLite multi table selection

Hi I try to select data from 2 tables.

I want to select from bill the flatname where bill flatdescription is equal to buildingflats flatname.

Here is my code

        t.executeSql('SELECT * FROM buildingflats WHERE buildingcode = ? ORDER BY flatname ASC',[buildingcode], function(t, resultflatcomment) {
            var j,
                lenflatcomments = resultflatcomment.rows.length,
                rowflatcomments,
                row;

            if (lenflatcomments > 0 ) {
                for (j = 0; j < lenflatcomments; j += 1) {
                    rowflatcomments = resultflatcomment.rows.item(j);
                    alert(rowflatcomments.flatname);
                    t.executeSql('SELECT DISTINCT flatdescription, flatname, buildingcode FROM bill WHERE buildingcode = ? AND flatdescription = ?',[buildingcode, rowflatcomments.flatname], function(t, resultflat) {
                        var len = resultflat.rows.length;

                        if (len > 0) {
                            row = resultflat.rows.item(0);
                            //alert(row.flatdescription);
                            //alert(row.flatname);
                            $('#opt2').append('<option value="' + row.flatdescription + '">'  + row.flatdescription + '...' + row.flatname +  '</option>');
                        } else {
                            //alert(rowflatcomments.flatname);
                            $('#opt2').append('<option value="' + rowflatcomments.flatname + '">' + rowflatcomments.flatname +  '</option>');
                        }
                        $("#opt2").selectmenu('refresh');
                    });
                }
            }
        });

The problem is that if len is equal to zero I receive always the last buildingflats flatname.

Where am I wrong??