递归 CTE |查找 redshift 表中所有 id 的超级父 id

Question

我有一个表组织，其中有“id”，“parent_id” 我需要在 redshift 表中找到“id”列的超级父 id 。

输入表：

id	parent_id
a1	空
b1	c1
c1	a1
d1	空

输出表：

id	parent_id	super_parent_id
a1	空	空
b1	c1	a1
c1	a1	a1
d1	空	空

我已经尝试过了

with RECURSIVE ParentHierarchy(id, parent_id, super_parent_id) AS (
  SELECT id, parent_id, id AS super_parent_id
  FROM org
  WHERE parent_id IS NULL

  UNION ALL

  SELECT t.id as id , t.parent_id as parent_id, ph.super_parent_id as super_parent_id
  FROM org t
  JOIN ParentHierarchy ph ON t.parent_id = ph.id
)
SELECT ph.id, ph.parent_id, ph.super_parent_id AS super_parent_id
FROM ParentHierarchy ph

我无法得到预期的结果。你能纠正我吗？

提前致谢

Answer 1

您的查询几乎是正确的；唯一需要的调整是仅当父项不为空时才选择 super_parent_id :

WITH RECURSIVE ParentHierarchy(id, parent_id, super_parent_id) AS (
  SELECT id, parent_id, id AS super_parent_id
  FROM org
  WHERE parent_id IS NULL
  UNION ALL
  SELECT t.id as id , t.parent_id as parent_id, ph.super_parent_id as super_parent_id
  FROM org t
  JOIN ParentHierarchy ph ON t.parent_id = ph.id
)
SELECT id, parent_id, CASE WHEN parent_id IS NOT NULL THEN super_parent_id ELSE NULL END AS super_parent_id
FROM ParentHierarchy ph
ORDER BY id;

我建议使用自连接查询而不是递归查询：

SELECT O1.id, o1.parent_id, COALESCE(o2.parent_id, o2.id) AS super_parent_id
FROM org o1
LEFT JOIN org o2 ON o1.parent_id = o2.id