SELECT *
FROM tbl t1
WHERE NOT EXISTS (SELECT * FROM tbl t2 
                           WHERE t1.Node1=t2.Node2
                                 AND t1.Node2=t2.Node1
                                 AND t2.Node1>t1.Node1)

with
o as (select case when Node1<=Node2 then Node1 else Node2 end as N1
           , case when Node1<=Node2 then Node2 else Node1 end as N2
        from aTable
     )

select N1, N2 from o group by N1, N2

with aTable as (
     select *
       from (values ('a', 'b'),
                    ('a', 'c'),
                    ('a', 'c'),
                    ('a', 'a'),
                    ('b', 'a'),
                    ('c', 'a')
            ) as T(Node1,Node2)

)
,o as (select case when Node1<=Node2 then Node1 else Node2 end as N1
             ,case when Node1<=Node2 then Node2 else Node1 end as N2
         from aTable
)

select distinct N1, N2 from o --group by N1, N2

select distinct N1, N2 from o

select N1, N2 from o

-- расписание игр по списку
  
create table players (nom int, name varchar(20));
 
insert into players (nom,name) values(1,'СПАРТАК');  
insert into players (nom,name) values(2,'ЦСКА');    
insert into players (nom,name) values(3,'ДИНАМО');
insert into players (nom,name) values(4,'ЗЕНИТ');
 
        
select t1.name, t2.name from Players t1
  join Players t2 on  t1.nom > t2.nom   

with aTable as (
     select *
       from (values ('a', 'b', 'c'),
                    ('a', 'c', 'b'),
                    ('a', 'c', 'c'),
                    ('a', 'a', 'a'),
                    ('b', 'a', 'a'),
                    ('c', 'a', 'a')
            ) as T(Node1,Node2,Node3)

)
,o as (
	select 
			Node1 = (SELECT t.Node FROM (values (aTable.Node1),(aTable.Node2),(aTable.Node2)) t(Node) ORDER BY Node OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY),
			Node2 = (SELECT t.Node FROM (values (aTable.Node1),(aTable.Node2),(aTable.Node2)) t(Node) ORDER BY Node OFFSET 1 ROWS FETCH NEXT 1 ROWS ONLY),
			Node3 = (SELECT t.Node FROM (values (aTable.Node1),(aTable.Node2),(aTable.Node2)) t(Node) ORDER BY Node OFFSET 2 ROWS FETCH NEXT 1 ROWS ONLY) 
	FROM aTable
)
select DISTINCT Node1,Node2,Node3 from o 

declare @t table (node1 char, node2 char)
insert into @t values ('a','c'),('a','b'),('c','a')

select node1, node2 from @t
except
select node2, node1 from @t