On form level:
I think setup a filter guide to loop short description and add comma into it.
On DB level:
Concatenate queries can do this.
please try this -
1. Take one table field on the form.(which will retrieve the required records with help of correct table qualification)
2. write one activelink to set the value in field A. (Set field action - Field A + "," + Column Short Description)
3. And run this activelink in loop with the help of AL Guide. And one activelink to run AL guide.