CREATE TABLE T
(
ID BIGINT PRIMORY KEY,
ST_DT DATETIME,
ED_DT DATETIME,
)
CREATE TABLE S
(
ID BIGINT PRIMORY KEY,
ST_DT DATETIME,
ED_DT DATETIME,
)

declare @T TABLE 
(
ID BIGINT ,
ST_DT DATETIME,
ED_DT DATETIME
)
declare @S TABLE 
(
ID BIGINT ,
ST_DT DATETIME,
ED_DT DATETIME
)

insert @T
select 1, '20100101', '20110101'

insert @S
select 1, '20100201', '20100501'
union all
select 1, '20100701', '20100815'

declare @b table (id int, d DATETIME, n int identity primary key clustered)
declare @e table (id int, d DATETIME, n int identity primary key clustered)

insert @b (id, d)
select ID, ED_DT from @S
union all
select ID, ST_DT from @T T where ST_DT<(select min(ST_DT) from @S x where x.ID=T.ID )
order by 1, 2

select * from @b

insert @e (id, d)
select ID, ST_DT from @S
union all
select ID, ED_DT from @T T where ED_DT>(select max(ED_DT) from @S x where x.ID=T.ID )
order by 1, 2

select * from @e

select b.d ST, e.d EN
from @b b inner join @e e on b.n=e.n -- and b.id=e.id

use tempdb
go

create table t(
	id int
	,startDate datetime2
	,endDate datetime2
)

create table s(
	id int
	,startDate datetime2
	,endDate datetime2
)

insert into t values (1, '20100101', '20110101')
insert into s values (1, '20100201', '20100501'),(2, '20100701', '20100815') 

;with d as (
	select *, row_number() over (order by q.dd) rnb from(
	select t.startDate dd from t
	union
	select t.endDate from t
	union
	select s.startDate from s
	union
	select s.endDate from s
	) as q
)
select dl.dd, dr.dd from d dl join d dr on dl.rnb = dr.rnb - 1
except
select s.startDate, s.endDate from s

drop table t
drop table s