declare @xref table (GroupID int, ItemID int)
insert into @xref
	select 1, 1 union
	select 1, 2 union
	select 1, 3 union
	select 2, 4 union
	select 2, 5 

declare @in table (GroupID int, ItemID int)
insert into @in
	select 1, 3 union
	select 2, 1 union
	select 2, 5 

-- For GroupID = 1 should return ItemIDs (1, 2)
-- for GroupID = 2 should return ItemIDs (4)

select distinct d.*
from	(	select * from @xref
		except
		select * from @in
	)d
join	@in i on
	d.GroupID = i.GroupID


-- desired results:

GroupID     ItemID
----------- -----------
1           1
1           2
2           4

select * from @xref
except
select * from @in

quote:

---

Originally posted by Peso

This only will do

select * from @xref
except
select * from @in

---

E 12°55'05.25"
N 56°04'39.16"

---

declare @in table (GroupID int, ItemID int)
insert into @in
	select 1, 3

-- desired resultset:

GroupID     ItemID
----------- -----------
1           1
1           2