Cursor To Increment A Value In A New Column

I am trying to update a new column called "sorting", with incremented values
strating at 1 for the first row and 2 for the second and 3 for the thirsd etc......., before doing that I need the table to be sorted using three
columns. I am using a cursor but it is not working I need your help.
Thanks in advance:

CODE:

set @ordering_count=0
declare review_test_cursor cursor scroll keyset for

select oid,decision_date,ranking,sorting,decision_id
from DECISION_FLAGS
order by oid,decision_date,ranking asc

open review_test_cursor
fetch next from review_test_cursor

while (@@fetch_status = 0 )
Begin
update DECISION_FLAGS
set sorting = CAST ((@ordering_count + 1) as VARCHAR)
set @ordering_count = @ordering_count + 1

fetch next from review_test_cursor
end

close review_test_cursor
deallocate review_test_cursor