CSV user column

Possibly, as is my specific case, I need invoices and receipts to be made from different points of sale, where at the end of the day I would be informed by exporting the CSV that was charged and who it was.
It would be nice to add a user column, which is definitely a minor change and adds up a lot. Better yet, it would be able to select which columns I want to export in the CSV.
Cheers!