DECLARE @T TABLE (ID int Identity(1,1), Start int, Finish int)

INSERT INTO @T (Start, Finish)
SELECT 1, 5
UNION ALL
SELECT 1, 3
UNION ALL
SELECT 1, 2
UNION ALL
SELECT 1, 9
UNION ALL
SELECT 11, 20
UNION ALL
SELECT 15, 19
UNION ALL
SELECT 15, 25
UNION ALL
SELECT 30, 40
UNION ALL
SELECT 29, 41
select * from @t

;with
   s as ( select start, row_number() over(order by start) n from @t t where not exists( select * from @t tt where (tt.start<t.start or (tt.start=t.start and tt.id<t.id) ) and tt.finish > t.start) )
,  f as ( select finish, row_number() over(order by finish) n from @t t where not exists( select * from @t tt where (tt.finish>t.finish or (tt.finish=t.finish and tt.id>t.id) ) and tt.start < t.finish) )
select start, finish from s inner join f on s.n = f.n

BEGIN
	WITH S AS 
	(
		SELECT [start],ROW_NUMBER()
		OVER 
		(	
			ORDER BY [start]
		) AS [RN] 
		FROM @t T1
		WHERE NOT EXISTS(
							SELECT TOP 1 1 
							FROM @t T2
							WHERE (T2.[start] < T1.[start] AND T2.[finish] > T1.[start])

							UNION ALL 

							SELECT TOP 1 1 
							FROM @t T2
							WHERE (T2.[start]=T1.[start] AND T2.[id] < T1.[id] AND T2.[finish] > T1.[start])
						) 
	),
	F AS 
	(
		SELECT [finish],ROW_NUMBER() 
		OVER 
		(	
			ORDER BY [finish]
		) AS [RN]
		FROM @t T1
		WHERE NOT EXISTS(
							SELECT TOP 1 1
							FROM @t T2 
							WHERE (T2.[finish] > T1.[finish] AND T2.[start] < T1.[finish])

							UNION ALL

							SELECT TOP 1 1
							FROM @t T2 
							WHERE (T2.[finish] = T1.[finish] AND T2.[id] > T1.[id] AND T2.[start] < T1.[finish])
						)
	)
	SELECT [start],[finish]
	FROM S 
	INNER JOIN F on S.[RN] = F.[RN]
END

DECLARE @T TABLE (ID int Identity(1,1), Start int, Finish int)

INSERT INTO @T (Start, Finish)
SELECT 1, 5
UNION ALL
SELECT 1, 3
UNION ALL
SELECT 1, 2
UNION ALL
SELECT 1, 9
UNION ALL
SELECT 11, 20
UNION ALL
SELECT 15, 19
UNION ALL
SELECT 15, 25
UNION ALL
SELECT 30, 40
UNION ALL
SELECT 29, 41

SELECT min(num) StartMin, max(num) FinishMax 
FROM (
	SELECT num
		,num - rank() OVER (
			ORDER BY num
			) n
	FROM (
		SELECT DISTINCT num
		FROM 

		(    SELECT 5*5*(a-1)+5*(b-1) + c AS num
			FROM (SELECT 1 a UNION ALL SELECT 2 UNION ALL SELECT 3
			UNION ALL SELECT 4 UNION ALL SELECT 5
			) x CROSS JOIN
			(SELECT 1 b UNION ALL SELECT 2 UNION ALL SELECT 3
			UNION ALL SELECT 4 UNION ALL SELECT 5
			) y CROSS JOIN
			(SELECT 1 c UNION ALL SELECT 2 UNION ALL SELECT 3
			UNION ALL SELECT 4 UNION ALL SELECT 5
			) z
			WHERE 5*5*(a-1)+5*(b-1) + c <= 100
		)  as s join @t t on s.num between start and Finish
)t
)tt
group by n

;with nums9 as
(select * from (values(0),(1),(2),(3),(4),(5),(6),(7),(8),(9))t(num))
, nums (num) as
(
select a.num+b.num*10+c.num*100+d.num*1000
from
	nums9 a,
	nums9 b,
	nums9 c,
	nums9 d
)
, list as
(
select distinct num
from nums n
join @t t
	on n.num between t.Start and t.Finish
)
select t1.num Start, min(t2.num) Finish
from list t1
join list t2
	on t1.num < t2.num
group by t1.num
having t1.num+1 <> min(t2.num)

select distinct
           (select min(t2.Start)  from @t as t2 where t1.Start between t2.Start and t2.Finish or t1.Finish between t2.Start and t2.Finish) as Start,
	   (select max(t2.Finish) from @t as t2 where t1.Start between t2.Start and t2.Finish or t1.Finish between t2.Start and t2.Finish) as Finish
  from @t as t1