declare @sql as nvarchar(max),@sql1 as nvarchar(max),@sql2 as nvarchar(max),@i as int,@j as int,@l as int,@tmp as nvarchar(max),@stri as nvarchar(5)

set @sql1='';

set @i=0 set @l=3 set @sql2='' while(@i<@l) begin  set @stri=cast(@i as nvarchar(5))  set @sql='declare @max'+@stri+' as table(id bigint,parentid int);  insert into @max'+@stri+'(id,parentid)  select max(id),parentid  from Products inner join Classes on Classes.classid=Products.classid  where parentid>0 '  set @j=0  set @tmp=''  while(@j<@i)  begin   set @tmp=@tmp+' and id not in(select id from @max'+cast(@j as nvarchar(5))+')'   set @j=@j+1  end  set @sql=@sql+@tmp+' group by ParentID;'  set @sql1=@sql1+@sql;  if(@i>0) set @sql2=@sql2+' union '  set @sql2=@sql2+'select * from @max'+@stri+' '  set @i=@i+1 end set @sql=@sql1+ 'select ProductName,ProductDpic,1 as indexID,Products.ID,UserName,RealName,Products.Addtime,ParentID from Products inner join Admin_User on Admin_User.id=Products.userid inner join ('+@sql2+') as t on t.id=products.id'

exec sp_executesql  @sql