declare @a varchar(8000),@b varchar(8000),@c varchar(8000)
set @a ='10,11,12' 
set @b='a,b' 
set @c='9' 


set @a = 'select '''+replace(@a,',',''' as col union select ''')+''' as col'
set @b = 'select '''+replace(@b,',',''' as col union select ''')+''' as col'
set @c = 'select '''+replace(@c,',',''' as col union select ''')+''' as col'
exec('select a.col,b.col,c.col from ('+@a+') a full join ('+@b+') b  on 1 =1 full join ('+@c+') c on 1= 1')

/*

col  col  col  
---- ---- ---- 
10   a    9
11   a    9
12   a    9
10   b    9
11   b    9
12   b    9

*/

create table tb(f1 varchar(10),f2 varchar(10),f3 varchar(10))
go
create proc pinsert(@a varchar(30),@b varchar(30),@c varchar(30))
as
begin
 declare @s varchar(8000)
 create table #a(id varchar(10))
 create table #b(id varchar(10))
 create table #c(id varchar(10))
 set @s = stuff(replace(','+@a,',',''' insert #a select '''),1,1,'')+''''
        + stuff(replace(','+@b,',',''' insert #b select '''),1,1,'')+''''
        + stuff(replace(','+@c,',',''' insert #c select '''),1,1,'')+''''
 exec(@s)
 insert tb select *  from #a,#b,#c
end
go
exec pinsert '1,2,3','a,b','9'
select * from tb
go
drop table tb
go
drop proc pinsert
/*
f1         f2         f3         
---------- ---------- ---------- 
1          a          9
2          a          9
3          a          9
1          b          9
2          b          9
3          b          9
*/