The export .ini file really just specifies SQL queries. So in the [COLUMNS] line, you can use the syntax of your database server to concatenate the 3 fields into one. Or make any other data transformation.
if you are limited to only three fields then a quick solution would be to setup three text fields and make a DB rule when all three exist then update the 255 custom field with the concatenation of all three... ************ I have just tested on my dev. environment, here is what the rule will look like:
When sr / inc is created or modified where surveycomment5 (*) is anything AND survey comment 7 (*) is anything AND survey comment 8 (*) is anything Concatenating three text fields (Update Data) Information set to (Concatenate [surveycomment5] With (Concatenate [survey comment 7] With [survey comment 8]))
Notice since you can not have a huge list of fields to concatenate you use the second field of the first as a call to function to concatenate the 2nd and 3rd.....
With a few seconds apart with our replies :) interesting idea I forgot that it can be done. I have not done it myself before but I would be interested in a small sample how to do it in the .ini file :)
I also am very interested in the option that Gyula Matics spoke of. That would be the most simple method for me. Custom fields are a rare (or difficult to find) and I wouldn't want to waste some by using them for weekly imports.
Oh, maybe that is the other thing I should have stated... This will be a weekly feed. Can I still use the delta processing on the 255 field if I'm merging things in via the ini?