set nocount on
use pubs
go
create table junk (Cli_ID int, Criteria int)
go

create function dbo.fn_criteriaByCliID(@cli_id int)
returns varchar(5000)
as
begin
	declare @out varchar(5000)
	select	@out = coalesce(@out + ',' + convert(varchar,criteria), convert(varchar,criteria))
	from	junk
	where	cli_id = @cli_id

	return @out
end

go
insert Junk
select 1,1 union all
select 1,2 union all
select 2,1 union all
select 2,2 union all
select 2,3 union all
select 3,1 union all
select 4,1 
go

select	cli_id, dbo.fn_criteriaByCliID(cli_id) criteria
from	(
	select	cli_id
	from	junk
	group by cli_id
	) a

go
drop function dbo.fn_criteriaByCliID
drop table junk

---------------------------------------
output:
cli_id      criteria   
----------- -----------
1           1,2
2           1,2,3
3           1
4           1