set statistics time on;
go
set statistics io on;
go

select
  i.name, stuff(f.x.value('.', 'nvarchar(4000)'), 1, 2, '') columns
from sys.indexes i  with(nolock)
cross join master..spt_values v
cross apply (
  select ', '+c.name
  from sys.index_columns ic with(nolock)
  join sys.columns c with(nolock) on c.object_id=ic.object_id and c.column_id=ic.column_id
  where ic.object_id=i.object_id and ic.index_id=i.index_id
  order by ic.key_ordinal
  for xml path(''), type
) f(x)
where i.type in (1,2) and v.type='P' and v.number between 1 and 100;

SQL Server parse and compile time: 
   CPU time = 16 ms, elapsed time = 17 ms.

(2518900 rows affected)
Table 'spt_values'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 8, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'syscolpars'. Scan count 0, logical reads 223578, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'sysiscols'. Scan count 25189, logical reads 76264, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'sysidxstats'. Scan count 1, logical reads 757, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 6396 ms,  elapsed time = 19098 ms.

create function dbo.fnIndexColumns(@object_id int, @index_id int)
returns nvarchar(4000)
as
begin
  declare
    @s nvarchar(4000);
  set @s='';
  select
    @s=@s+', '+c.name
  from sys.index_columns ic with(nolock)
  join sys.columns c with(nolock) on c.object_id=ic.object_id and c.column_id=ic.column_id
  where ic.object_id=@object_id and ic.index_id=@index_id
  order by ic.key_ordinal;
  if len(@s)>2
    set @s=stuff(@s, 1, 2, '');
  return @s;
end;
go

set statistics time on;
go
set statistics io on;
go
select
  i.name, dbo.fIndexColumns(i.object_id, i.index_id) columns
from sys.indexes i  with(nolock)
cross join master..spt_values v
where i.type in (1,2) and v.type='P' and v.number between 1 and 100;;

SQL Server parse and compile time: 
   CPU time = 13 ms, elapsed time = 13 ms.

(2518900 rows affected)
Table 'Worktable'. Scan count 1, logical reads 66800, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'sysidxstats'. Scan count 1, logical reads 757, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'spt_values'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 383310 ms,  elapsed time = 389880 ms.