declare @t table (i int)
declare @p table (p1 char(2), p2 char(2), p3 char(2), p4 char(2), p5 char(2))

insert @t (i)
select
	row_number()over(order by (select 1)) - 1
from
	(values (0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) t1(i)
	cross join (values (0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) t2(i)

insert @p (p1, p2, p3, p4, p5)
values
	('A1', 'B1', 'C1', 'D1', 'E1'),
	('A2', 'B2', 'C2', 'D2', 'E2'),
	('A3', 'B3', 'C3', 'D3', 'E3')

;
with
t1 as
	(
	select
	p1, p2, p3, rn + i as n
	from
	(
	select
	p1, p2, p3, row_number()over(order by (select 1)) as rn
	from
	@p p
	)q
	inner join @t t on t.i = q.rn - 1
	),
t2 as
	(
	select
	p4 as p1, p5 as p2, null as p3, rn + i as n
	from
	(
	select
	p4, p5, row_number()over(order by (select 1)) as rn
	from
	@p p
	)q
	inner join @t t on t.i = q.rn
	)

select
	p1, p2, p3, n
from
	t1
union all
select
	p1, p2, p3, n
from
	t2
order by
	n