declare @sebastian table(dcar int, make varchar(25), line varchar(25))

insert into @sebastian
select 1, 'audi', 'a4'
union
select 2, 'audi', 'a6'
union
select 3, 'audi', 's6'
union
select 4, 'audi', 'a8'
union
select 5, 'bmw', '318'
union
select 6, 'bmw', '320'
union
select 7, 'bmw', '325'


select * 
  from @sebastian
  
  
select make,

stuff(

(

select distinct ',[' + line + ']'

from @sebastian s2
where s2.make = s1.make
AND line <> 'a4'


for xml path('')


),1,1,'')  

from @sebastian s1
group by make