Can I append data to an existing Excel file when exporting data if I do not know the number of rows of the first select beforehand?
For the second select it is possible to specify which row of the Excel you want to start the export in, but when the number of rows the first select returns is unknown, it is hard to guess where to start the export.
In the SelectToFile activity there is an append option that will look for the existing rows and insert the next set of rows after previously entered rows. To use you need to have an existing file, deselect Overwrite. and choose Append rows and name the sheet where the rows go.