declare @t1 table
( 
   id1 int PRIMARY KEY,
   iFrom1 int,
   iTo1 int
)

declare @t2 table 
( 
   id2 int PRIMARY KEY,
   iFrom2 int,
   iTo2 int
)

insert into @t1 (id1, iFrom1, iTo1) values (1, 0, 10)
insert into @t1 (id1, iFrom1, iTo1) values (2, 10, 20)
insert into @t1 (id1, iFrom1, iTo1) values (3, 20, 30)

insert into @t2 (id2, iFrom2, iTo2) values (1, 0, 5)
insert into @t2 (id2, iFrom2, iTo2) values (2, 5, 15)
insert into @t2 (id2, iFrom2, iTo2) values (3, 15, 35)

select * from @t1
select * from @t2

declare @dbl table 
(
   i1 int,
   i2 int
)

insert into @dbl (i1, i2)
select dbl.i1, i2 = min(dbl.i2) from
(
   select i1.i1, i2.i2 from 
   (
      select i1 from 
      (
         select i1 = iFrom1 from @t1
         union all select iTo1 from @t1
         union all select iFrom2 from @t2
         union all select iTo2 from @t2
      ) i1
      group by i1
   ) i1
   left outer join (
      select i2 from 
      (
         select i2 from 
         (
            select i2 = iFrom1 from @t1
            union all select iTo1 from @t1
            union all select iFrom2 from @t2
            union all select iTo2 from @t2
         ) i2
         group by i2
      ) i2      
   ) i2
   on i1.i1 < i2.i2
) dbl
where i2 is not null
group by dbl.i1
having dbl.i1 is not null

select * from @dbl

select dbl.i1, dbl.i2, t1.iFrom1, t1.iTo1, t2.iFrom2, t2.iTo2
from @dbl dbl
left outer join @t1 t1 on (dbl.i1 + dbl.i2) / 2 between t1.iFrom1 and t1.iTo1 
left outer join @t2 t2 on (dbl.i1 + dbl.i2) / 2 between t2.iFrom2 and t2.iTo2
GO

i1	i2	iFrom1	iTo1	iFrom2	iTo2
0	5	0	10	0	5
5	10	0	10	5	15
10	15	10	20	5	15
15	20	10	20	15	35
20	30	20	30	15	35
30	35	NULL	NULL	15	35