How can I export only some columns from that ADOQuery to Excel using Delphi (any version)?

Question

I have an ADOQuery (TADOQuery, bound to other visual components) with multiple columns (fields), in Delphi. I can export all the data (rows and columns) to an Excel file. I'm using OleVariant, something like ovRange.CopyFromRecordset (Data, Rows, Cols). How can I export only some columns from an ADOQuery to Excel using Delphi (any version)?

procedure ExportRecordsetToMSExcel(const DestName: string; Data: _Recordset);
var
  ovExcelApp: OleVariant;
  ovExcelWorkbook: OleVariant;
  ovWS: OleVariant;
  ovRange: OleVariant;
  FileFormat: Integer;
  Cols, Rows: Cardinal;
begin
  FileFormat := ExcelFileTypeToInt(xlWorkbookDefault);
  ovExcelApp := CreateOleObject('Excel.Application'); // If Excel isnt installed will raise an exception

  try
    ovExcelWorkbook := ovExcelApp.WorkBooks.Add;
    ovWS := ovExcelWorkbook.Worksheets.Item[1]; // go to first worksheet
    ovWS.Activate;
    ovWS.Select;

    Rows := Data.RecordCount;
    Cols := Data.Fields.Count; // I don't want all of them, just some, maybe the ones that are visible

    ovRange := ovWS.Range['A1', 'A1']; // go to first cell
    ovRange.Resize[Rows, Cols]; //ovRange.Resize[Data.RecordCount, Data.Fields.Count];

    ovRange.CopyFromRecordset(Data, Rows, Cols); // this copy the entire recordset to the selected range in excel

    ovWS.SaveAs(DestName, FileFormat, '', '', False, False);
  finally
    ovExcelWorkbook.Close(SaveChanges := False);
    ovWS := Unassigned;
    ovExcelWorkbook := Unassigned;

    ovExcelApp.Quit;
    ovExcelApp := Unassigned;
  end;
end;
...
  ExportRecordsetToMSExcel('c:\temp\test.xlsx', ADOQuery.Recordset);

Resolved (working solution based on @MartynA and @PeterWolf's answers):

procedure ExportRecordsetToMSExcel(const DestName: string; ADOQuery: TADOQuery; const Fields: array of string); overload;

  procedure CopyData( { out } var Values: OleVariant);
  var
    R, C: Integer;
    FieldsNo: array of Integer;
    L1, H1, L2, H2: Integer;
    V: Variant;
    F: TField;
  begin
    L1 := 0;
    H1 := ADOQuery.RecordSet.RecordCount + L1 - 1;
    L2 := Low(Fields); // 0
    H2 := High(Fields);

    SetLength(FieldsNo, Length(Fields));
    for C := L2 to H2 do
      FieldsNo[C] := ADOQuery.FieldByName(Fields[C]).Index;

    Values := VarArrayCreate([L1, H1, L2, H2], varVariant);

    for R := L1 to H1 do begin
      for C := L2 to H2 do
        Values[R, C] := ADOQuery.RecordSet.Fields[FieldsNo[C]].Value;

      ADOQuery.RecordSet.MoveNext();
    end;
  end;

var
  ovExcelApp: OleVariant;
  ovExcelWorkbook: OleVariant;
  ovWS: OleVariant;
  ovRange: OleVariant;
  Values: OleVariant;
  RangeStr: string;
  Rows, Cols: Integer;
begin
  CopyData(Values);
  try
    ovExcelApp := CreateOleObject('Excel.Application');
    try
      ovExcelWorkbook := ovExcelApp.WorkBooks.Add;
      ovWS := ovExcelWorkbook.ActiveSheet;

      Rows := ADOQuery.RecordSet.RecordCount;
      Cols := Length(Fields);
      RangeStr := ToRange(1, 1, Rows, Cols); // Ex: 'A1:BE100'

      ovRange := ovWS.Range[RangeStr];
      ovRange.Value := Values;

      ovWS.SaveAs(FileName := DestName);
    finally
      ovExcelWorkbook.Close(SaveChanges := False);
      ovWS := Unassigned;
      ovExcelWorkbook := Unassigned;

      ovExcelApp.Quit;
      ovExcelApp := Unassigned;
    end;
  finally
    VarClear(Values);
  end;
end;

Answer 1

Update

I am obliged to Peter Wolf for the suggestion to use Excel's Transpose function to avoid the element by element copying in my initial code. Trying to implement it, I found I ran into a known problem with Transpose , that it throws a "Type mismatch" error if it encounters a Null in the array it is transposing. The updated code below has a work-around to this problem, and also removes a number of lines from the OP's code which seemed to me to be superfluous.

====

You can do what you are asking, without changing the SQL used to retrieve your recordset by using the recordset's GetRows method which is declared in AdoIntf.Pas as

function GetRows(Rows: Integer; Start: OleVariant; Fields: OleVariant): OleVariant; safecall;

This can retrieve the values from one or more named columns from the recordset into a variant array, as documented here: https://docs.microsoft.com/en-us/office/client-developer/access/desktop-database-reference/recordset-getrows-method-dao

A version of your routine modified to use recordset.GetRows might be

procedure ExportRecordsetToMSExcel(const DestName: string; Data: _Recordset);
var
  ovExcelApp: OleVariant;
  ovExcelWorkbook: OleVariant;
  ovWS: OleVariant;
  ovRange: OleVariant;
  Rows : Integer;
  FieldList : Variant;
  RSRows : OleVariant;
  i : Integer;
  Values : OleVariant;
begin
  ovExcelApp := CreateOleObject('Excel.Application');
  ovExcelApp.Visible := True; //  So we can see what's happening
  try
    ovExcelWorkbook := ovExcelApp.WorkBooks.Add;
    ovWS := ovExcelWorkbook.ActiveSheet;


    //  RecordSet.GetRows (see AdoIntf.Pas) can return one or more fields of the RS to a variant array
    FieldList := 'Name';
    RSRows := Data.GetRows(Data.RecordCount, '', 'name' );

    //  The values from the RS 'Name' field are now in the 2nd dimension of RSRows
    //  The following is a naive way of extracting these values to a Transposable array
    Values := VarArrayCreate([VarArrayLowBound(RSRows, 2), VarArrayHighBound(RSRows, 2)], varVariant);
    Rows := VarArrayHighBound(RSRows, 2) - VarArrayLowBound(RSRows, 2) + 1;

    for i := VarArrayLowBound(RSRows, 2) to VarArrayHighBound(RSRows, 2)  do begin
      Values[i] := RSRows[0, i];

      //  Note:  the next 2 lines are to avoid the known problem that calling Excel's Transpose
      //         will generate a "Type mismatch" error when the array bring transposed contains Nullss
      if VarIsNull(Values[i]) then
        Values[i] := '';
    end;

    //  Now, transpose Values into the destination range (the 'A' column) using Excel's built-in function
    ovWS.Range['A1:A' + IntToStr(Rows)] := ovExcelApp.Transpose(Values);

    ShowMessage(' here');
  finally
    ovExcelWorkbook.Close(SaveChanges := False); //  Abandon changes to avoid tedium in debugging
    ovWS := Unassigned;
    ovExcelWorkbook := Unassigned;

    ovExcelApp.Quit;
    ovExcelApp := Unassigned;
  end;
end;

As noted in the code's comments, this extracts the Name column of the Sql table I happened to by using for this answer.

Please note R Hoek's comment about bracketing the call to your bound dataset's Open method by calls to DisableControls and EnableControls , as this will likely have as big an impact on speed as the method you use to import the column(s) into Excel.