OK - it does not matter that the source and destination are the same.
insert into myTable
(QuestId, MagId, ProfId, AnsId, Comments, GroupCode)
Select QuestId, MagId, 'new value for ProfId' as ProfId, AnsId, Comments, GroupCode
from
myTable T2
where T2.IsNew = 1 -- obviously, subsitute your own logic in the where clause
If you simply execute this against the server rather than bringing everything locally and iterating through each record it will be MUCH faster
