create table #groups(id int identity, name varchar(10))
insert into #groups(name) values('group 1')
insert into #groups(name) values('group 2')

create table #products(id int identity, name varchar(10))
insert into #products(name) values('product 1')
insert into #products(name) values('product 2')
insert into #products(name) values('product 3')
insert into #products(name) values('product 4')

create table #temp1(group_id int, product_id int)
insert into #temp1 values(1, 1)
insert into #temp1 values(1, 2)
insert into #temp1 values(2, 3)


/*All products with group*/
select * from
#groups a
inner join #temp1 b on b.group_id = a.id
inner join #products c on b.product_id = c.id

/*All products without group*/
select *
from #products a
left outer join #temp1 b on b.product_id = a.id
where b.product_id is null

drop table #groups
drop table #products
drop table #temp1