Cấu trúc phân cấp trong SQL server 2005 với XML

Bạn có thể sử dụng CTE đệ quy để xây dựng hệ thống phân cấp và lặp qua các cấp để xây dựng XML.

-- Sample data
create table MyDatabaseTable(ID int,  Name varchar(10), Parent int, [Order] int)
insert into MyDatabaseTable values
(1, 'N1',     null, 1),
(2, 'N1_1',   1   , 1),
(3, 'N1_1_1', 2   , 1),
(4, 'N1_1_2', 2   , 2),
(5, 'N1_2',   1   , 2),
(6, 'N2',     null, 1),
(7, 'N2_1',   6   , 1)

-- set @Root to whatever node should be root
declare @Root int = 1

-- Worktable that holds temp xml data and level
declare @Tree table(ID int, Parent int, [Order] int, [Level] int, XMLCol xml)

-- Recursive cte that builds @tree
;with Tree as 
(
  select 
    M.ID,
    M.Parent,
    M.[Order],
    1 as [Level]
  from MyDatabaseTable as M
  where M.ID = @Root
  union all
  select 
    M.ID,
    M.Parent,
    M.[Order],
    Tree.[Level]+1 as [Level]
  from MyDatabaseTable as M
    inner join Tree
      on Tree.ID = M.Parent  
)
insert into @Tree(ID, Parent, [Order], [Level])
select *
from Tree


declare @Level int
select @Level = max([Level]) from @Tree

-- Loop for each level
while @Level > 0
begin

  update Tree set
    XMLCol = (select
                M.ID as '@ID',
                M.Name as '@Name',
                M.Parent as '@Parent',
                M.[Order] as '@Order',
                (select XMLCol as '*'
                 from @Tree as Tree2
                 where Tree2.Parent = M.ID
                 order by Tree2.[Order]
                 for xml path(''), type)
              from MyDatabaseTable as M
              where M.ID = Tree.ID
              order by M.[Order]
              for xml path('item'))
  from @Tree as Tree             
  where Tree.[Level] = @Level

  set @Level = @Level - 1
end

select XMLCol
from @Tree
where ID = @Root

Kết quả

<item ID="1" Name="N1" Order="1">
  <item ID="2" Name="N1_1" Parent="1" Order="1">
    <item ID="3" Name="N1_1_1" Parent="2" Order="1" />
    <item ID="4" Name="N1_1_2" Parent="2" Order="2" />
  </item>
  <item ID="5" Name="N1_2" Parent="1" Order="2" />
</item>