SQL Server:GROUP BY hai cấp với đầu ra XML

declare @T table
(
  ID int,
  Type varchar(30),
  SubType varchar(30),
  SubSubType varchar(30)
)

insert into @T values
(1, 'Product Documentation', 'Brochures',                'Functional Brochures'),
(2, 'Product Documentation', 'Brochures',                'Fliers'),
(3, 'Product Documentation', 'Data Sheets and Catalogs', 'Data Sheets'),
(4, 'Product Documentation', 'Data Sheets and Catalogs', 'Catalogs'),
(5, 'Other Documentation',   'Other classification',     'User Guides')

select T1.Type as '@Name',
       (
       select T2.SubType as '@Name',
              (
              select T3.SubSubType as '@Name'
              from @T as T3
              where T3.SubType = T2.SubType and
                    T3.Type = T1.Type
              for xml path('SubSubType'), type
              )
       from @T as T2
       where T2.Type = T1.Type
       group by T2.SubType
       for xml path('SubType'), type
       )
from @T as T1
group by Type
for xml path('Type'), root('AllTypes')