Any question answered...

The subjects might have had more than one occurrence unfortunately.

The only way I can think to group them is to reference the row below.

I could potentially use a for loop with this logic.

Counter =0
For i in number_of_rows:
  If enddate[i]+1 = startdate [i+1]:
    grp_num[i] = n
  elif:
    num = num+1
    grp_num[i] = num

Any issues with doing loops in SQL? Will it kill everything?