[ecfisa]

Hola.

Creo que buscas algo así:

Código Delphi [-]
...
var
  j: Integer;
begin
   FDQuery.Close;
   FDQuery.SQL.Text := 'SELECT COUNT(*) AS CONT FROM detalle_venta';
   FDQuery.Active := True;
   StringGrid1.RowCount := FDQuery.FieldByName('CONT').AsInteger;

   FDQuery.Close;
   FDQuery.SQL.Clear;
   FDQuery.SQL.Add('SELECT can_det FROM detalle_venta');
   FDQuery.SQL.Add('WHERE id_ven_det = :ID_DETS');
   FDQuery.ParamByName('ID_DETS').AsInteger := ID_VENTA;
   FDQuery.Active := True;

   j := StringGrid1.FixedRows;
   while not FDQuery.Eof do
   begin
     StringGrid1.Cells[0, j] := FDQuery.FieldByName('can_det').AsString;
     FDQuery.Next;
     Inc(j);
   end;
  ...

Saludos