Question

我有自引用表 - HIERARCHY(id, name, parent_id)。因此，我需要通过此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，它可以通过此树的任何节点获取所有树，例如根h1，例如按h1_2

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

我写了这个问题：

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 - 将子树从子节点返回到父节点（包括），
hierarchy_with_children - 返回所有树。

似乎一切正常，但我不是数据库专家，我想知道有关我的查询的限制和评论。对PostgreSQL和Oracle 11g的任何其他解决方案也欢迎。

感谢。

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因子子查询中完成的。然后只需收集链接到该根的所有行。如果NVL()已经是根，我需要在外部查询中进行:input_node调用;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），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;

如何通过任何节点获取树（SQL）

1 个答案: