Declare @D table(Id int identity( 1, 1 ),NStart int, NEnd int)
Declare @Vid table(Id int, Num int)

Insert into @D values
(1,10),
(50,100)

Insert into @Vid Values
(1, 5),
(1 ,7),
(2, 55),
(2, 56)


;With cte as
(
Select  Id, Nstart as Num,NEnd from @D
union all
Select Id, Num + 1 Num,NEnd from CTE where Num+1<=NEnd
)
select Id,Num from cte
where Num not in (select Num from @Vid v Where v.Id = cte.Id)
order by Id,Num

Insert into @D values
(1,10),
(1,20)

select Id,Num,NEnd from cte

Declare @D table(Id int identity( 1, 1 ),NStart int, NEnd int)
Declare @Vid table(Id int, Num int)

Insert into @D values
(1,10),
(50,100)

Insert into @Vid Values
(1, 5),
(1 ,7),
(2, 55),
(2, 56)
;
with
x as ( 
select Num from @Vid v1 
  where not exists(select * from @Vid v2 where v2.Num = v1.Num +1 )
        and v1.Num < (select max(Num) from @Vid)
union         
select Num from @Vid v1 
  where not exists(select * from @Vid v2 where v2.Num = v1.Num -1 )
        and v1.Num > (select min(Num) from @Vid)
),
y as (select *, ROW_NUMBER() over(Order by Num) n from x)
select y1.Num+1 [from], y2.Num-1 [to] from y y1 inner join y y2 on y1.n+1 = y2.n