как присвоить родительские ИД ? (дерево)

use test

if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[Upr]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)

drop table [dbo].[Upr]

GO



CREATE TABLE [Upr]([ID] [int] NOT NULL ,[lvl] [int] NOT NULL ,[pos] [int] NOT NULL, [ParentID] [int] NOT NULL) ON [PRIMARY]



INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(11,0, 1, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(12,1, 2, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(13,1, 3, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(14,1, 4, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(15,2, 5, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(16,0, 6, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(17,1, 7, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(18,2, 8, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(19,2, 9, 0)

INSERT INTO Upr (ID, lvl, pos, ParentID) VALUES(20,3, 10,0)

ID          lvl         pos         ParentID    

----------- ----------- ----------- ----------- 


11          0           1           0

12          1           2           11

13          1           3           11

14          1           4           11

15          2           5           14

16          0           6           0

17          1           7           16

18          2           8           17

19          2           9           17

20          3           10         19

SELECT	Ch.ID AS Ch_ID, Ch.lvl AS Ch_lvl, Ch.pos AS Ch_pos, 

	Pr.ID AS Pr_ID, Pr.lvl AS Pr_lvl, Pr.pos As Pr_pos  

FROM Upr Ch

Inner JOIN Upr Pr ON (Ch.lvl = Pr.lvl+1) AND (Ch.pos > Pr.pos)

order by Ch.pos

update Upr set ParentID = (select top 1 ID from Upr u2 where Upr.lvl=u2.lvl+1 and Upr.ID>u2.ID order by ID desc) where lvl<>0