The record sort expert sorts records not groups.
group sorts happen then the remaining rows inside the group are sorted using the record sort criteria.
There is a seperate Group sort expert.
Since you did not indicate how you want to sort a group that has multiple last names I can't really answer the question.
However the group sort expert can use group summary results to sort on.
If you insert a min or max value of the last name for the SSN group you can use that result to sort the SSN groups.
Edited by DBlank - 05 Mar 2014 at 4:13am