具有递归的 Postgres - 结果包括祖父母和孙子女

Question

我的家谱包含 children 和 parents。我可以使用 postgres with recursive 为给定的人编写一个 returns grandchildren 的查询。但是我怎样才能在结果中包括祖父母呢？我的目标是报告祖父母 id 分组的祖父 children 的数量。如何在最终结果中引用查询的 non-recursive 部分？

已编辑 - 示例 table：

child parent
  11   null
  12   null
  13   null
  21    11
  22    11
  31    12
  32    12
  33    12
  41    13
  81    21
  82    21
  83    21
  91    33
  92    33

non-recursive 部分查询：

select distinct child where parent is null -- as grandparent

期望的结果：

grandparent, grandchildren
     11           3
     12           2
     13           0

Answer 1

这样做：

with recursive zzz AS (
  select child AS grandparent, child AS current_child, 1 AS grand_level 
  FROM thetable AS tt
  where parent is null
 UNION
  SELECT grandparent, tt.child, grand_level+1
  FROM thetable AS tt
  JOIN zzz
    ON tt.parent = zzz.current_child
)
SELECT grandparent, COUNT(DISTINCT current_child)FILTER(WHERE grand_level = 3) AS grandchildren
FROM zzz
GROUP BY grandparent;

具有递归的 Postgres - 结果包括祖父母和孙子女

Postgres with recursive - result to include both grandparent and grandchildren

postgresql

recursive-query

with-statement