如何在表中为多个层次结构获取根节点及其所有子节点

Question

我在DB

中有以下层次结构

A
|_A1
|  |_A11
|
|_A2

和

B
|_B1
|
|_B2
   |_B21
   |_B22

我想要一个显示结果为

的查询

Parent    Child
A          A1
A          A11
A          A2
B          B1
B          B2
B          B21
B          B22

Answer 1

with w(child, parent) as
(
  select 'A', null from dual
  union all
  select 'A1', 'A' from dual
  union all
  select 'A11', 'A1' from dual
  union all
  select 'A2', 'A' from dual
  union all
  select 'B', null from dual
  union all
  select 'B1', 'B' from dual
  union all
  select 'B2', 'B' from dual
  union all
  select 'B21', 'B2' from dual
  union all
  select 'B22', 'B2' from dual
)
select connect_by_root child parent, child
from w
connect by w.parent = prior w.child
start with w.parent is null
;

返回：

1   A   A
2   A   A1
3   A   A11
4   A   A2
5   B   B
6   B   B1
7   B   B2
8   B   B21
9   B   B22

您可以在where connect_by_root child != child和from之间添加connect来过滤包含parent == child的行。