declare @t table (id1 int, id2 int, id3 int, id4 int)
insert into @t values
	(11,12,13,14)
	,(21,22,23,24)
	,(31,32,33,34)
	,(41,42,43,44)

declare @q table (p int)
insert into @q values (1),(3)

;with cte as (
	select 
		val, cast(substring(id,3,100) as int) as id 
	from @t t
	unpivot (val for id in(id1, id2, id3, id4)) as unpvt 
)
select * from cte 
where id in (select p from @q)

declare @SQL nvarchar(max)=''

select @SQL=@SQL+case when @SQL<>'' then ' union all ' else '' end + 'select id'+cast(p as nvarchar)+' from @t' from @q
print @SQL	-- select id1 from @t union all select id3 from @t
exec (@SQL)