create table tb1(a varchar(10),b,varchar(10))

insert into tb1 select 'A01',    '001'
insert into tb1 select 'A01',    '002'
insert into tb1 select '001',    '0001'
insert into tb1 select '001',    '0002'
insert into tb1 select '001',    '0003'
insert into tb1 select '0002',    '00005'
insert into tb1 select 'A08',    '001'
insert into tb1 select 'A08',    '002'

select * from tb1


上表是一个工程bom的表结构
比如 我现在需要查A01的表结构
就查询A01下面有几个料号，在查子料号下面又有几个料号，一直搜索到下面没有料号为止
最后得到下面的数据，若第一列有重复，则为null



A01    001
    002
001    0001
    0002
    0003
0002    00005    
A08    001
    002
001    0001
    0002
    0003
0002    00005

--测试数据
DECLARE @t TABLE(ID char(3),PID char(3),Name nvarchar(10))
INSERT @t SELECT '001',NULL ,'山东省'
UNION ALL SELECT '002','001','烟台市'
UNION ALL SELECT '004','002','招远市'
UNION ALL SELECT '003','001','青岛市'
UNION ALL SELECT '005',NULL ,'四会市'
UNION ALL SELECT '006','005','清远市'
UNION ALL SELECT '007','006','小分市'

--深度排序显示处理
--生成每个节点的编码累计(相同当单编号法的编码)
DECLARE @t_Level TABLE(ID char(3),Level int,Sort varchar(8000))
DECLARE @Level int
SET @Level=0
INSERT @t_Level SELECT ID,@Level,ID
FROM @t
WHERE PID IS NULL
WHILE @@ROWCOUNT>0
BEGIN
    SET @Level=@Level+1
    INSERT @t_Level SELECT a.ID,@Level,b.Sort+a.ID
    FROM @t a,@t_Level b
    WHERE a.PID=b.ID
        AND b.Level=@Level-1
END

--显示结果
SELECT SPACE(b.Level*2)+'|--'+a.Name
FROM @t a,@t_Level b
WHERE a.ID=b.ID
ORDER BY b.Sort
/*--结果
|--山东省
  |--烟台市
    |--招远市
  |--青岛市
|--四会市
  |--清远市
    |--小分市
--*/

------解决方案--------------------

SQL code

create table tb1(a varchar(10),b varchar(10))

insert into tb1 select 'A01',    '001'
insert into tb1 select 'A01',    '002'
insert into tb1 select '001',    '0001'
insert into tb1 select '001',    '0002'
insert into tb1 select '001',    '0003'
insert into tb1 select '0002',    '00005'
insert into tb1 select 'A08',    '001'
insert into tb1 select 'A08',    '002'
go

;with cte as
(
    select *,cast(a as varchar(max)) as lev from tb1 t where not exists (select 1 from tb1 where b=t.a)
    union all
    select a.*,b.lev + '01'
    from tb1 a join cte b on a.a = b.b
),ach as
(
    select *,px=row_number() over (partition by a,lev order by b)
    from cte
)

select (case when px=1 then a else '' end) a,b
from ach
order by lev,px

drop table tb1

/**************************

a          b
---------- ----------
A01        001
           002
001        0001
           0002
           0003
0002       00005
A08        001
           002
001        0001
           0002
           0003
0002       00005

(12 行受影响)