oracle 递归查询一个树形结构的菜单

关键字：oracle connect by level 树状结构表
定义如下id 和 名称描述
1— 省长 <--- 2,3 (省长管辖市长、县长)
2— 市长 <--- 5,6 (市长管辖模范村村长和一个平民)
3— 县长 <--- 4,7,8,9 (县长管辖镇长和三个平民)
4— 镇长 <--- 10,11,12,13 (管辖四个平民)
5— 村长 <--- 14,15 (管辖两个平民)
其他(6-15)— 平民(没有管辖任何人)

只有省长、市长和县长能处理问题，那么每个人出了问题应该首先找谁来解决？
省长权利最大，自己出了问题自己解决，别人也没法知道; 可以认为在关系表里省长的父节点是自己。

create table person(id int primary key, description varchar2(50));
create table relationship(child int, parent int, primary key(child,parent));
insert into person values(1,‘省长’);
insert into person values(2,‘市长’);
insert into person values(3,‘县长’);
insert into person values(4,‘镇长’);
insert into person values(5,‘村长’);
insert into person values(6,‘平民’);
...//省略的都是平民
insert into person values(15,‘平民’);

insert into relationship values(1,1); //关系如下
insert into relationship values(2,1);
insert into relationship values(3,1);
insert into relationship values(5,2);
insert into relationship values(6,2);
insert into relationship values(4,3);
insert into relationship values(7,3);
insert into relationship values(8,3);
insert into relationship values(9,3);
insert into relationship values(10,4);
insert into relationship values(11,4);
insert into relationship values(12,4);
insert into relationship values(13,4);
insert into relationship values(14,5);
insert into relationship values(15,5);

create table person(id int primary key, description varchar2(50));
create table relationship(child int, parent int, primary key(child,parent));
insert into person values(1,‘省长’);
insert into person values(2,‘市长’);
insert into person values(3,‘县长’);
insert into person values(4,‘镇长’);
insert into person values(5,‘村长’);
insert into person values(6,‘平民’);
...//省略的都是平民
insert into person values(15,‘平民’);

insert into relationship values(1,1); //关系如下
insert into relationship values(2,1);
insert into relationship values(3,1);
insert into relationship values(5,2);
insert into relationship values(6,2);
insert into relationship values(4,3);
insert into relationship values(7,3);
insert into relationship values(8,3);
insert into relationship values(9,3);
insert into relationship values(10,4);
insert into relationship values(11,4);
insert into relationship values(12,4);
insert into relationship values(13,4);
insert into relationship values(14,5);
insert into relationship values(15,5);

查看一下关系树：

select rpad('---',(level-1)*3,'---')||child relation_tree
from relationship
start with child=parent
connect by nocycle prior child=parent; --结果如下
RELATION_TREE
------------------
1
---2
------5
---------14
---------15
------6
---3
------4
---------10
---------11
---------12
---------13
------7
------8
------9

已选择15行。

select rpad('---',(level-1)*3,'---')||child relation_tree
from relationship
start with child=parent
connect by nocycle prior child=parent; --结果如下
RELATION_TREE
------------------
1
---2
------5
---------14
---------15
------6
---3
------4
---------10
---------11
---------12
---------13
------7
------8
------9

已选择15行。

查看父子关系情况：

select child,parent
from relationship
start with child=parent
connect by nocycle prior child=parent
order by parent; --结果如下
 CHILD     PARENT
---------- ----------
         1          1
         2          1
         3          1
         5          2
         6          2
         4          3
         8          3
         7          3
         9          3
        11          4
        12          4
        10          4
        13          4
        14          5
        15          5

已选择15行。

select child,parent
from relationship
start with child=parent
connect by nocycle prior child=parent
order by parent; --结果如下
 CHILD     PARENT
---------- ----------
         1          1
         2          1
         3          1
         5          2
         6          2
         4          3
         8          3
         7          3
         9          3
        11          4
        12          4
        10          4
        13          4
        14          5
        15          5

已选择15行。

下面要看一看：每个人有事时，首先找到谁来处理？不能每个人有事都找省长吧。
下面的sql使用了oracle家的两个变态函数：first_value &　connect_by_root

select distinct child ,first_value(parent)over(partition by child order by lv) parent
from(
    select connect_by_root(r.child) child, p.description descr, level lv, r.parent
    from person p ,relationship r
    where p.id= r.parent
    connect by nocycle prior r.parent=r.child
 )
where descr in('省长', '市长', '县长')
order by parent,child; --结果如下
     CHILD     PARENT
---------- ----------
         1          1
         2          1
         3          1
         5          2
         6          2
        14          2
        15          2
         4          3
         7          3
         8          3
         9          3
        10          3
        11          3
        12          3
        13          3

已选择15行。

select distinct child ,first_value(parent)over(partition by child order by lv) parent
from(
    select connect_by_root(r.child) child, p.description descr, level lv, r.parent
 	from person p ,relationship r
 	where p.id= r.parent
 	connect by nocycle prior r.parent=r.child
 )
where descr in('省长', '市长', '县长')
order by parent,child; --结果如下
     CHILD     PARENT
---------- ----------
         1          1
         2          1
         3          1
         5          2
         6          2
        14          2
        15          2
         4          3
         7          3
         8          3
         9          3
        10          3
        11          3
        12          3
        13          3

已选择15行。

这个sql到底行不行，再加条数据看看

insert into person values(333,‘县长’);
insert into person values(555,‘村长’);
insert into person values(666,‘平民’);
insert into person values(777,‘平民’);

insert into relationship values(333,1);
insert into relationship values(555,333);
insert into relationship values(666, 555);
insert into relationship values(777,666);
              --666这个平民有￥，777愿意跟着他（这条记录比较特殊）