declare @num table (NUMBER varchar(20) not null primary key clustered)

insert into @num (NUMBER)
select n from (
select n=0 union all select 1 union all select 2 union all
select   3 union all select 4 union all select 5 union all
select   6 union all select 7 union all select 8 union all
select   9 ) n

declare @s1 varchar(25)
declare @s2 varchar(25)
select  @s1 = '', @s2 = ''

select
	@s1 = @s1 + NUMBER + '_' ,
	@s2 = '_' + @s2 + NUMBER
from
	@num
order by
	NUMBER

select S1 = @s1, S2 = @s2

S1                        S2                        
------------------------- ------------------------- 
0_1_2_3_4_5_6_7_8_9_      __________0123456789