多级节点查询子集的问题

如下所示：

CREATE FUNCTION [dbo].[getMaterialTable](@PID VARCHAR(32))  
RETURNS TABLE
AS
RETURN 
(
with CID as
(
	select  CAST(SMC.ROW_ID AS VARCHAR(1000)) AS PX_CODE,
			SMC.*
	from SD_MATERIAL_CATEGORY SMC where SMC.ROW_ID=@PID
	union all 
	(select CAST(SMC1.PX_CODE+SMC2.ROW_ID AS VARCHAR(1000)),
			SMC2.* from CID SMC1, SD_MATERIAL_CATEGORY SMC2
	where SMC1.ROW_ID=SMC2.PARENT_CATEGORY_ID 
	)
 )
SELECT * FROM CID 
);
GO