DECLARE @a TABLE (
	id_row int identity (1, 1) 
	,col1 NVARCHAR(10)
	,col2 NVARCHAR(10)
	)

insert into @a
values ('А', 'Б')
insert into @a
values ('А', 'В')
insert into @a
values ('Г', 'Б')
insert into @a
values ('Г', 'А')
insert into @a
values ('Ж', 'А')
insert into @a
values ('В', 'Д')
insert into @a
values ('Ж', 'В')
insert into @a
values ('П', 'У');
insert into @a
values ('У', 'К');
insert into @a
values ('Е', 'Г');

with cte as -- выбор соседних значений
(
	select col2 col, id_row from @a   -- Добавление значений вторых столбцов, иначе не попадут
	union
	select t2.col1, t1.id_row    -- соединяем с самим мобой по разноименным стобцам, выбираем значения одноименного
	from (select col1, min (id_row) id_row from @a group by col1) t1
	join  @a t2
	on t1.col1 = t2.col2
	union
	select t2.col1, t1.id_row  -- соединяем с самим мобой по одноименным стобцам, выбираем значения разноименного
	from (select col1, min (id_row) id_row from @a group by col1) t1
	join  @a t2
	on t1.col1 = t2.col1 
)

select
min(c1.id_row), 
c3.col 
from cte c1
join cte c2 on c1.col = c2.col  -- соединяем по значению, в  случае, если пересечения происходит через более чем одну итерацию
join cte c3 on c2.id_row = c3.id_row -- получаем все соседние значения для найденого на предыдущем уровне соответсвия
group by c3.col

with A as (--исходные данные
  select *
    from (values ('А', 'Б'),
                 ('А', 'В'),
                 ('Г', 'Б'),
                 ('Г', 'А'),
                 ('Ж', 'А'),
                 ('В', 'Д'),
                 ('Ж', 'В'),
                 ('П', 'У'),
                 ('У', 'К'),
                 ('Е', 'Г')
         ) as T(m,n)
)
, B as (--упорядочиваем по столбцам
  select m,n
        ,case when m<=n then m else n end as m1
        ,case when m<=n then n else m end as n1
    from A
)
select dense_rank() over (order by m1) as r
      ,m1,n1
      ,'',m,n
  from B
 order by r,n1

r	m1	n1	 	m	n
1	А	Б		А	Б
1	А	В		А	В
1	А	Г		Г	А
1	А	Ж		Ж	А
2	Б	Г		Г	Б
3	В	Д		В	Д
3	В	Ж		Ж	В
4	Г	Е		Е	Г
5	К	У		У	К
6	П	У		П	У

DECLARE @a TABLE (
	id_row int identity (1, 1) 
	,col1 NVARCHAR(10)
	,col2 NVARCHAR(10)
	,Cluster INT NULL 
	)

insert into @a(col1, col2)
values ('А', 'Б')
insert into @a(col1, col2)
values ('А', 'В')
insert into @a(col1, col2)
values ('Г', 'Б')
insert into @a(col1, col2)
values ('Г', 'А')
insert into @a(col1, col2)
values ('Ж', 'А')
insert into @a(col1, col2)
values ('В', 'Д')
insert into @a(col1, col2)
values ('Ж', 'В')
insert into @a(col1, col2)
values ('П', 'У');
insert into @a(col1, col2)
values ('У', 'К');
insert into @a(col1, col2)
values ('Е', 'Г');

UPDATE @a
SET Cluster = id_row

WHILE @@ROWCOUNT > 0
BEGIN 
	UPDATE a
	SET a.Cluster = a1.Cluster
	FROM @a a
	INNER JOIN @a a1 ON (a.col1 = a1.col2 OR a.col2 = a1.col1) AND a.Cluster < a1.Cluster 
END 

SELECT * FROM @a

declare @a  TABLE (
	id_row int identity (1, 1) 
	,col1 NVARCHAR(10)
	,col2 NVARCHAR(10)
	,rk int 
	)

DECLARE @output  TABLE (
	col NVARCHAR(10)
	,rk int
	,rk_min int 
	)

insert into @a (col1, col2) values ('А', 'Б')
insert into @a (col1, col2) values ('А', 'В')
insert into @a (col1, col2) values ('Г', 'Б')
insert into @a (col1, col2) values ('Г', 'А')
insert into @a (col1, col2) values ('Ж', 'А')
insert into @a (col1, col2) values ('В', 'Д')
insert into @a (col1, col2) values ('Ж', 'В')
insert into @a (col1, col2) values ('П', 'У');
insert into @a (col1, col2) values ('У', 'К');
insert into @a (col1, col2) values ('Е', 'Г');
insert into @a (col1, col2) values ('Б', 'Ю');
insert into @a (col1, col2) values ('Ю', 'Э');
insert into @a (col1, col2) values ('Э', '?');
insert into @a (col1, col2) values ('1', '2');
insert into @a (col1, col2) values ('2', '1');
insert into @a (col1, col2) values ('3', '2');

declare @column nvarchar(100)
declare @rk int = 1

DECLARE curs CURSOR FOR 
select * from
(
	SELECT col1 cl
	FROM @a
	union
	SELECT col2 cl
	FROM @a
) s
order by cl 

OPEN curs

FETCH NEXT FROM curs 
INTO @column

WHILE @@FETCH_STATUS = 0
BEGIN

	IF NOT EXISTS (select  * from @output where col = @column)
	BEGIN
		INSERT INTO @output
		VALUES (@column, @rk, @rk)
		SET @rk = @rk + 1
	END

	insert into 
	@output
	select 
	t2.col2, t1.rk, rk_min
	from 
	(select distinct col, rk, min(rk) over (partition by col) rk_min from @output) t1
	join @a t2
	on t1.col = t2.col1
	and t2.col1 = @column
	

	insert into 
	@output
	select 
	t2.col1, t1.rk, rk_min
	from  
	(select distinct col, rk, min(rk) over (partition by col) rk_min from @output) t1
	join @a t2
	on t1.col = t2.col2
	and t2.col2 = @column
	
	

FETCH NEXT FROM curs 
INTO @column
END
CLOSE curs
DEALLOCATE curs;


select distinct col, min(rk_min) over (partition by rk)
from @output

select col1, col2, id_row + 0 gr into #ttt from @a

while @@ROWCOUNT >0
begin
	update t set gr = a.gr
	from #ttt t join #ttt a on (a.col1 in (t.col1, t.col2) or a.col2 in (t.col1, t.col2)) and a.gr > t.gr
end			

select col, dense_rank() over(order by MAX(gr)) gr
from (select col1 col, gr from #ttt union all select col2, gr from #ttt)t
group by col 

select
min(c1.id_row), 

select
dense_rank() over(order by min(c1.id_row)),