----------------------------------------------------------------------------------
-- Author : htl258(Tony)
-- Date : 2011-05-19 17:25:59
-- Version: Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86)
-- Jul 9 2008 14:43:34
-- Copyright (c) 1988-2008 Microsoft Corporation
-- Developer Edition on Windows NT 5.1 (Build 2600: Service Pack 2)
-- Blog : http://blog.csdn.net/htl258
----------------------------------------------------------------------------------
--> 生成测试数据表: [Tree]
IF OBJECT_ID([Tree]) IS NOT NULL
DROP TABLE [Tree]
GO
CREATE TABLE [Tree] ([ID] [int],[Text] [nvarchar](10),[PID] [int])
INSERT INTO [Tree]
SELECT 1,A,NULL UNION ALL
SELECT 2,B,1 UNION ALL
SELECT 3,C,2 UNION ALL
SELECT 4,D,3

--SELECT * FROM [Tree]
GO
-->SQL查询如下:

IF OBJECT_ID(getdpt)>0
DROP FUNCTION getdpt
GO
CREATE FUNCTION GetDPT(@Id INT)
RETURNS NVARCHAR(200)
AS
BEGIN
DECLARE @dptn NVARCHAR(50), @dpti NVARCHAR(20)
SELECT @dptn = [Text], @dpti = PID
FROM Tree
WHERE ID = @Id
RETURN
CASE
WHEN ISNULL(@dpti, )= THEN @dptn
ELSE ISNULL(dbo.GetDPT(@dpti)+->, )+@dptn
END
END
GO

SELECT dbo.GetDPT(4)
/*
A->B->C->D

(1 行受影响)
*/