sql - 如何通过任意节点获取树(SQL)

Question

我有自引用表 - HIERARCHY(id, name, parent_id)。 所以我需要通过该层次结构的任何节点获取所有层次结构。例如我们有树，其中 h1, h2 是根:

-(h1)
  | |_(h1_1)
  | |   |_(h1_1_2)
  | |_(h1_2)
  |    |_(h1_2_1)
-(h2)
  | |_(h2_1)
  | |_(h2_2)   
  |     

我需要的是通过这棵树的任何节点获取所有树，例如根 h1通过 h1_2

     -(h1)
        |_(h1_1)
get     |   |_(h1_1_2)    by h1_2 or h1_2_1, etc
        |_(h1_2)
           |_(h1_2_1)

我写了查询:

WITH RECURSIVE hierarchy_with_parents(id) AS (
  SELECT l.id, l.name, l.parent_id FROM hierarchy AS l WHERE l.id = <any_row_id>
  UNION ALL
  SELECT lc.id, lc.name, lc.parent_id FROM hierarchy lc, hierarchy_with_parents lwp WHERE lc.id = lwp.parent_id
), hierarchy_with_children(id) AS (
  SELECT l.id, l.name, l.parent_id FROM hierarchy AS l WHERE l.id 
  IN ( -- sub-query for getting parent id
    SELECT
    lwp.id
    FROM hierarchy_with_parents AS lwp
    WHERE lwp.parent_id IS NULL
  )
  UNION ALL
  SELECT lc.id, lc.name, lc.parent_id FROM hierarchy lc, hierarchy_with_children lwc WHERE lc.parent_id = lwc.id
)
SELECT * FROM hierarchy_with_children

hierarchy_with_parents - 将子树从子树返回到父树(包括)，
hierarchy_with_children - 返回所有树。

似乎一切正常，但我不是 DB 专家，我想知道关于我的查询的限制和评论。也欢迎任何其他适用于 PostgreSQL 和 Oracle 11g 的解决方案。

谢谢。

Answer 1

给定 :input_node，首先找到包含该节点的子树的根。这是在 find_root 分解子查询中完成的。然后简单地收集所有链接到该根的行。我需要在外部查询中调用 NVL() 以防 :input_node 已经是根；在这种情况下，find_root 不返回任何行。当用作标量子查询时，它被视为 null(至少在 Oracle 中是这样)，因此我可以使用 NVL() 来修复它。

with
     hierarchy as (
       select 2 as child, 1  as parent from dual union all
       select 3, 2 from dual union all
       select 4, 1 from dual union all
       select 5, 4 from dual union all
       select 7, 6 from dual union all
       select 8, 7 from dual union all
       select 9, 6 from dual
     ),
     find_root as (
       select parent as rt
       from hierarchy
       where connect_by_isleaf = 1       
       start with child = :input_node
       connect by child = prior parent
     ) 
select child, parent
from   hierarchy
start with parent = nvl((select rt from find_root), :input_node)
connect by parent = prior child;