declare  @i int, @qty int,@j int
set @i=98;
select char(97) as entity,1 as etype into ttb
union
select char(97) as entity,2 as etype
while(@i<110)
 begin
  set @qty=1+cast(10*rand() as int)
  set @j=1;
  while(@j<=@qty)
    begin
	 insert ttb values(char(@i),@j)
	 set @j=@j+1
	end
  set @i=@i+1
 end

select
 *, runningcount / 20 + 1
from
 Таблица

create table #t (num varchar(1), cnt int)
insert #t values
('a',	9),
('b',	7),
('c',	9),
('d',	3),
('e',	7),
('f',	4),
('g',	5)

select *, 
sum(cnt) over(order by num) / 19 группа
from #t

create table #t (num varchar(1), cnt int)
insert #t values
('a',	9),
('b',	7),
('c',	12),
('d',	9),
('e',	7),
('f',	4),
('g',	5)

select *, 
sum(cnt) over(order by num) / 19 группа,
SUM(cnt) OVER (ORDER BY cnt ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS RunningTotal 
from #t
ORDER BY sum(cnt) over(order by num) / 19
GO 

DROP table #t

create table #t (num varchar(1), cnt int)
insert #t values
('a',	5),
('b',	22),
('c',	41),
('d',	53),
('e',	63),
('f',	67),
('g',	72)
select *,
round ((((lag(cnt, 1, 0) over(order by num) * 1.0) % 20 + cnt * 1.0) / 20), 0) + 1, -- для 2008+
round ((((isnull((select top 1 cnt from #t where num < t.num order by num desc), 0) * 1.0) % 20 + cnt * 1.0) / 20), 0) + 1 --для всех
from #t t