1 数据准备
create table area_test(
id number(10) not null,
parent_id number(10),
name varchar2(255) not null
);
alter table area_test add (constraint district_pk primary key (id));
insert into area_test (ID, PARENT_ID, NAME) values (1, null, '中国');
insert into area_test (ID, PARENT_ID, NAME) values (11, 1, '河南省');
insert into area_test (ID, PARENT_ID, NAME) values (12, 1, '北京市');
insert into area_test (ID, PARENT_ID, NAME) values (111, 11, '郑州市');
insert into area_test (ID, PARENT_ID, NAME) values (112, 11, '平顶山市');
insert into area_test (ID, PARENT_ID, NAME) values (113, 11, '洛阳市');
insert into area_test (ID, PARENT_ID, NAME) values (114, 11, '新乡市');
insert into area_test (ID, PARENT_ID, NAME) values (115, 11, '南阳市');
insert into area_test (ID, PARENT_ID, NAME) values (121, 12, '朝阳区');
insert into area_test (ID, PARENT_ID, NAME) values (122, 12, '昌平区');
insert into area_test (ID, PARENT_ID, NAME) values (1111, 111, '二七区');
insert into area_test (ID, PARENT_ID, NAME) values (1112, 111, '中原区');
insert into area_test (ID, PARENT_ID, NAME) values (1113, 111, '新郑市');
insert into area_test (ID, PARENT_ID, NAME) values (1114, 111, '经开区');
insert into area_test (ID, PARENT_ID, NAME) values (1115, 111, '金水区');
insert into area_test (ID, PARENT_ID, NAME) values (1121, 112, '湛河区');
insert into area_test (ID, PARENT_ID, NAME) values (1122, 112, '舞钢市');
insert into area_test (ID, PARENT_ID, NAME) values (1123, 112, '宝丰市');
insert into area_test (ID, PARENT_ID, NAME) values (11221, 1122, '尚店镇');
2 start with connect by prior递归查询
2.1 查询所有子节点
select *
from area_test
start with name ='郑州市'
connect by prior id=parent_id
2.2 查询所有父节点
select t.*,level
from area_test t
start with name ='郑州市'
connect by prior t.parent_id=t.id
order by level asc;
start with 子句：遍历起始条件，如果要查父结点，这里可以用子结点的列，反之亦然。
connect by 子句：连接条件。prior 跟父节点列parentid放在一起，就是往父结点方向遍历；prior 跟子结点列subid放在一起，则往叶子结点方向遍历。parent_id、id两列谁放在“=”前都无所谓，关键是prior跟谁在一起。
order by 子句：排序。
2.3 查询指定节点的，根节点
select d.*,
connect_by_root(d.id) rootid,
connect_by_root(d.name) rootname
from area_test d
where name='二七区'
start with d.parent_id IS NULL
connect by prior d.id=d.parent_id
2.4 查询巴中市下行政组织递归路径
select id, parent_id, name, sys_connect_by_path(name, '->') namepath, level
from area_test
start with name = '平顶山市'
connect by prior id = parent_id
3 with递归查询
3.1 with递归子类
with tmp(id, parent_id, name)
as (
select id, parent_id, name
from area_test
where name = '平顶山市'
union all
select d.id, d.parent_id, d.name
from tmp, area_test d
where tmp.id = d.parent_id
)
select * from tmp;
3.2 递归父类
with tmp(id, parent_id, name)
as
(
select id, parent_id, name
from area_test
where name = '二七区'
union all
select d.id, d.parent_id, d.name
from tmp, area_test d
where tmp.parent_id = d.id
)
select * from tmp;
补充：实例
我们称表中的数据存在父子关系，通过列与列来关联的，这样的数据结构为树结构。
现在有一个menu表，字段有id，pid，title三个。
查询菜单id为10的所有子菜单。
SELECT * FROM tb_menu m START WITH m.id=10 CONNECT BY m.pid=PRIOR m.id;
将PRIOR关键字放在m.id前面，意思就是查询pid是当前记录id的记录，如此顺延找到所有子节点。
查询菜单id为40的所有父菜单。
SELECT * FROM tb_menu m START WITH m.id=40 CONNECT BY PRIOR m.pid= m.id ORDER BY ID;
总结
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