create table #t1(id int identity(1, 1), name varchar(10))

insert #t1(name)
values	('10'), ('максим'), ('56'), ('вася'), ('13'), ('даша'), ('8000'), ('76'), ('123'), ('12222'), ('44'), ('нет'), ('20'), ('14444'), ('1444455')

create table #t2(id int identity(1, 1), list varchar(50))

select
STUFF(ISNULL(CAST(( 
	SELECT ','+cast(Col as varchar)
	FROM mytable p
	order by col
	for xml path('') 
) as xml).value('.', 'varchar(max)'),''),1,1,'')

select
 *,
 sum(len(name) + <длина разделителя>) over (order by id) / <размерность поля list> as grp
from
 #t1;

select
 *,
 sum(len(name) + <длина разделителя>) over (order by id) / <размерность поля list> as grp
from
 #t1;

select 4/5, (4+4)/5, (4+4+4)/5, (4+4+4+4)/5, (4+4+4+4+4)/5, (4+4+4+4+4+4)/5

----------- ----------- ----------- ----------- ----------- -----------
0           1           2           3           4           4

	select t1.id i1,t2.id i2,sm
	from #t1 t1 join #t1 t2 on t1.id<t2.id
	outer apply (select SUM(LEN(name)+1)-1 from #t1 where id between t1.id and t2.id) S(sm)
	where sm<=10

with T as
(
	select t1.id i1,MAX(t2.id) i2,MAX(sm) sm,ROW_NUMBER() OVER(order by t1.id,MAX(t2.id))%2 Ch
	from #t1 t1 join #t1 t2 on t1.id<=t2.id
	outer apply (select SUM(LEN(name)+1)-1 from #t1 where id between t1.id and t2.id) S(sm)
	where sm<=10
	group by t1.id
)
select * from
(
	select IIF( LAG(i2) OVER(order by i1,i2) >= i1,i1+1,i1) i1,i2 from
	(
		select i1,i2,sm,LEAD(NxtD) OVER(order by i1,i2) prevN,LAG(NxtD) OVER(order by i1,i2) nxtN,Ch from
		(
			select i1,i2,sm,IIF (LEAD(i1) OVER(order by i1,i2) between i1 and i2  ,1,0) NxtD,Ch 
			from T T1
		) Z3
	) Z4
	where not(prevN=1 and nxtN=1 and ch=0)
) Z4
where i2>=i1
order by i1,i2

use tempdb
go

IF OBJECT_ID('tempdb..#t1') IS NOT NULL
    DROP TABLE #t1
--

create table #t1(id int identity(1, 1), name varchar(10), gr int, TotalRunLen int)

insert #t1(name)values ('10')
insert #t1(name)values ('максим')
insert #t1(name)values ('56')
insert #t1(name)values ('вася')
insert #t1(name)values ('13')
insert #t1(name)values ('даша')
insert #t1(name)values ('8000')
insert #t1(name)values ('76')
insert #t1(name)values ('123')
insert #t1(name)values ('12222')
insert #t1(name)values ('44')
insert #t1(name)values ('нет')
insert #t1(name)values ('20')
insert #t1(name)values ('14444')
insert #t1(name)values ('1444455')

--------------------------------------
declare @ListLen int;		set @ListLen = 20	--	Размер поля "получателя"
declare @Delim varchar(10);	set @Delim = '_'	--	Разделитель	

declare @gr int;			set @gr = 0
declare @TotalRunLen int;	set @TotalRunLen = 0

--------------------------------------
;with cte as
	(select top(2147483647) * from #t1 order by id)

update cte
set 
	 @gr = gr = @gr +	
				case 
					when @TotalRunLen+len(name) = @ListLen then 0 
					when @TotalRunLen+len(name)+len(@Delim) > @ListLen then 1 
					else 0
				end

	,@TotalRunLen = TotalRunLen =	
				case 
					when @TotalRunLen+len(name) = @ListLen then @TotalRunLen+len(name)
					when @TotalRunLen+len(name)+len(@Delim) > @ListLen then len(name)+len(@Delim) 
					else @TotalRunLen+len(name)+len(@Delim) 
				end
--output inserted.*

select * from #t1

id          name       gr          TotalRunLen
----------- ---------- ----------- -----------
1           10         0           3
2           максим     0           10
3           56         0           13
4           вася       0           18
5           13         0           20
6           даша       1           5
7           8000       1           10
8           76         1           13
9           123        1           17
10          12222      2           6
11          44         2           9
12          нет        2           13
13          20         2           16
14          14444      3           6
15          1444455    3           14

(15 row(s) affected)