sql problem more difficult to appear in the forum: 21 (recursion retrieve all the leaf nodes under a node)

Original: SQL problem more difficult to appear in the forum: 21 (recursion retrieve all the leaf nodes under a node)

Recently, in the forum, I met a lot more difficult sql problem, although they can be resolved, but found a few days later, they can not remember, forget the solution of.

So, I feel the need to be recorded, so that after the encounter this problem again, and get answers from the idea.

Problem: Find the SQL: retrieve all the leaf nodes under a node

Department table name: tb_department
the above mentioned id int - node of the above mentioned id
pid int - the parent node of the above mentioned id
Caption VARCHAR (50) - the department name
----------------------- --------------
the above mentioned id pid Caption
--------------------------------- -------------
1 0       AA
20     1      BB
64 20     CC
22     1      DD
23      22     The
24 1       FF
25     0      GG
26     1      HH
27     25     II
---------------- ---------------- tree follows

------------ --------------------------
Q: how to retrieve all of the most end of the leaf nodes under a node.
For example: to retrieve all the nodes under the tail end node AA CC, EE, FF, HH?

My solution for 2005 and above versions sql server:

   
   
create table tb_department(
id int, --节点id
pid int, --父节点id
caption varchar( 50) --部门名称
)

insert into tb_department
select 1 , 0 , 'AA' union all
select 20 , 1 , 'BB' union all
select 64 , 20 , 'CC' union all
select 22 , 1 , 'DD' union all
select 23 , 22 , 'EE' union all
select 24 , 1 , 'FF' union all
select 25 , 0 , 'GG' union all
select 26 , 1 , 'HH' union all
select 27 , 25 , 'II'
go


;with t
as
(
select id,pid,caption
from tb_department
where caption = 'AA'

union all

select t1.id,t1.pid,t1.caption
from t
inner join tb_department t1
on t.id = t1.pid
)

select *
from t
where not exists( select 1 from tb_department t1 where t1.pid = t.id)
/*
id pid caption
24 1 FF
26 1 HH
23 22 EE
64 20 CC
*/
  
  

If it is sql server 2000, how to write it:

   
   
--1.建表
create table tb_department(
id int, --节点id
pid int, --父节点id
caption varchar( 50) --部门名称
)

insert into tb_department
select 1 , 0 , 'AA' union all
select 20 , 1 , 'BB' union all
select 64 , 20 , 'CC' union all
select 22 , 1 , 'DD' union all
select 23 , 22 , 'EE' union all
select 24 , 1 , 'FF' union all
select 25 , 0 , 'GG' union all
select 26 , 1 , 'HH' union all
select 27 , 25 , 'II'
go


--2.定义表变量
declare @tb table
( id int, --节点id
pid int, --父节点id
caption varchar( 50), --部门名称
level int --层级
)


--3.递归开始
insert into @tb
select *, 1 as level
from tb_department
where caption = 'AA'


--4.递归的过程
while @@ROWCOUNT > 0
begin

insert into @tb
select t1.id,t1.pid,t1.caption, level + 1
from @tb t
inner join tb_department t1
on t.id = t1.pid
where not exists( select 1 from @tb t2
where t.level < t2.level)
end


--5.最后查询
select *
from @tb t
where not exists( select 1 from tb_department t1 where t1.pid = t.id)
/*
id pid caption level
24 1 FF 2
26 1 HH 2
64 20 CC 3
23 22 EE 3
*/