declare @d datetime, @d1 datetime, @d2 datetime,@d3 datetime,@d4 datetime
declare @cnt int
declare @t int
set @t =  1000000 
 ---------------------------------------
 
Set @cnt= 0 
select @d = getdate()
while @cnt<@t
  begin
    if EXISTS (select  1  from dbo.syscolumns)
      begin 
        Set @cnt=@cnt+ 1 
      end
  end
 -------------------------------------
 
Set @cnt= 0 
select @d1 = getdate()
while @cnt<@t
  begin
    if EXISTS (select * from dbo.syscolumns) 
      begin
        Set @cnt=@cnt+ 1 
      end
  end
 -------------------------------------
 
Set @cnt= 0 
select @d2 = getdate()
while @cnt<@t
  begin
    if EXISTS (select top  1   1  from dbo.syscolumns) 
      begin 
        Set @cnt=@cnt+ 1 
      end
  end
 -------------------------------------
 
Set @cnt= 0 
select @d3 = getdate()
while @cnt<@t
  begin
    if EXISTS (select top  1  * from dbo.syscolumns) 
      begin 
        Set @cnt=@cnt+ 1 
      end
  end
 -------------------------------------
 
select @d4 = getdate()

select  datediff(ms, @d, @d1) as '1',
	datediff(ms, @d1, @d2) as '*',
	datediff(ms, @d2, @d3) as 'top 1 1',
	datediff(ms, @d3, @d4) as 'top 1 *'