Hierarchy in SQL server 2005 with XML

Question

I wonder is there anyway to select hierarchy in SQL server 2005 and return xml format? I have a database with a lot of data (about 2000 to 3000 records), and i am now using a function in SQL server 2005 to retrieve the data in hierarchy and return an XML but it seems not perfect because it's too slow when there is a lot of data

Here is my function

Database

ID      Name      Parent       Order

Function

 CREATE FUNCTION [dbo].[GetXMLTree]
(
    @PARENT bigint
)
RETURNS XML
AS
    BEGIN
    RETURN /* value */
(SELECT [ID] AS "@ID",
        [Name] AS "@Name",
        [Parent] AS "@Parent",
        [Order] AS "@Order",
        dbo.GetXMLTree(Parent).query('/xml/item')
    FROM MyDatabaseTable
    WHERE [Parent]=@PARENT
    ORDER BY [Order]
    FOR XML PATH('item'),ROOT('xml'),TYPE)
    END

I would like to use XML in hierarchy because with me there's alot of thing to do with it :) Any best solutions plzzzzz

Answer 1

You can use a recursive CTE to build the hierarchy and loop over levels to build the 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

Result

<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>