Creating a 'foreach' style loop in pipelines

Your simplest solution would be as Mark suggested in this post and utilize a helper table to build your upsert. 

A more complex solution would be to use a for loop (in theory so don't hold me to it 100%) that might look like:  

{% set payload = [] %} OR [%set payload = '' %}

{% for i in range(a.counter_field) %}

build a json object you put into the payload or append a csv row if you go the importfromcsv route

{% endfor %}

The idea is to set an arbitrary array or string and loop through your counter to build a collection for upsert (REST API) or CSV string to use ImportFromCSV (HTTP API). It would be very difficult to test but you could try and build the payload on the fly inside of the Quickbase Request Channel body input.