EXEC('select '+@ColNames+'
from (select a.N, b.dummy, b.v from Test a cross apply (values (1, a.P), (2, a.B)) b(dummy, v)) t
PIVOT 
(min([v]) for N in (' + @ColNames + ')) p')

use tempdb
go

declare @SQL nvarchar(MAX)
declare @ColNames nvarchar(max)

create table Test (N int, P int)

insert into Test
 (N, P)
 select
  a.N, a.P
 from
  (
   select top (30)
    row_number() over (order by (select 1)),
    rand(checksum(newid())) * 1000
   from
    master.dbo.spt_values a cross join
    master.dbo.spt_values b
   ) a(N, P) cross apply
   (select top (cast(rand(checksum(newid(), a.P)) * 3 + 1 as int)) 1 from master.dbo.spt_values) b(c);

select * from Test order by N;

select
 @ColNames = stuff(t.x.value('.', 'nvarchar(max)'), 1, 2, '')
from
 (select ', ' + quotename(cast(N as sysname)) from (select distinct N from Test) a order by N for xml path(''), type) t(x);

set statistics time on;
exec('select ' + @ColNames + '
from (select N, P, row_number() over (partition by N order by (select 1)) from Test) t(N, P, g)
pivot 
(min(P) for N in (' + @ColNames + ')) p');
set statistics time off;
go

drop table Test;
go