BOM数据排序及分级显示

--示例数据:
CREATE TABLE BomSub(Parent_item varchar(10),Sub_item varchar(10))
INSERT BomSub SELECT 'A'  ,'AA'
UNION  ALL    SELECT 'A'  ,'AB'
UNION  ALL    SELECT 'AA' ,'AAA'
UNION  ALL    SELECT 'AA' ,'AAB'
GO

问题描述:
    Parent_item是父项，Sub_item是子项，根据根据父子关系排序，并生成每个项目的层次。对于示例数据，要求结果如下：
Parent_item  LEVEL
----------- -------
A           0
|-AA        1
|--AAA      2
|--AAB      2
|-AB        1

（所影响的行数为 5 行）

--查询处理的存储过程
CREATE PROC P_QRY
AS
DECLARE @t TABLE(Parent_item varchar(10),Level int,Path varchar(8000))
DECLARE @l int
SET @l=0
INSERT @t SELECT DISTINCT Parent_item,@l,RIGHT(SPACE(20)+Parent_item,20)
FROM BomSub a
WHERE NOT EXISTS(
    SELECT * FROM BomSub WHERE Sub_item=a.Parent_item)
WHILE @@ROWCOUNT>0
BEGIN
    SET @l=@l+1
    INSERT @t SELECT a.Sub_item,@l,b.Path+RIGHT(SPACE(20)+a.Sub_item,20)
    FROM BomSub a,@t b
    WHERE a.Parent_item=b.Parent_item AND b.Level=@l-1
END
SELECT Parent_item=CASE Level WHEN 0 THEN '' ELSE '|'+REPLICATE('-',Level) END+Parent_item,
    Level
FROM @t
ORDER BY Path
GO

--调用
EXEC P_QRY

1.I want to figure out that what is the ' @@ROWCOUNT

--SQL Code1:
insert bomsub select'B','BB'
union select'BB','BBB'

DECLARE @t TABLE(Parent_item varchar(10),Level int,Path varchar(8000))
DECLARE @l int
SET @l=0
INSERT @t SELECT DISTINCT Parent_item,@l,RIGHT(SPACE(20)+Parent_item,20)
FROM BomSub a
WHERE NOT EXISTS(
    SELECT * FROM BomSub WHERE Sub_item=a.Parent_item)
 

select  @@ROWCOUNT

select *
from @t

select *
from bomsub
/*
No column name
 2

parent_item  level  path
A             0      A
B             0      B