使用 postgresql 查询递归

Question

我正在尝试获取 grandparent 数据的结束 child 数据。

我有不到 2 tables，一个是具有 parent 和 child 数据的主 table，另一个是主 table 数据的关系 table。

根据这些数据，我想要 parent 数据及其结尾 child 数据。

为此，我尝试了以下递归查询，但没有获得任何相关数据。

最后我想在 java 批处理中以下面的方式使用这些数据。

如果我将child_data 331和327一一通过，那么它会分别提供以下结果。

@set ko_id = '331'

select parent_id,child_id,count(parent_id) from (
 WITH RECURSIVE ancestors (parent_id) AS (
  SELECT distinct t.parent_id ,t.parent_id as extra_id,t.child_id , msok.data_type -- and find all its ancestors
  FROM public.data_relation AS t 
    JOIN data_relation AS a ON t.child_id = a.parent_id or t.child_id = a.child_id 
    left join data_master msok on msok.id = t.parent_id
  where a.child_id = :ko_id
), 
descendants (parent_id) AS (
  SELECT  parent_id ,extra_id as extra_id,child_id, data_type FROM ancestors  
  UNION ALL
  SELECT t.child_id,d.parent_id as extra_id,t.child_id, msok.data_type -- and find all their descendants
  FROM public.data_relation AS t 
    JOIN descendants AS d ON t.parent_id = d.parent_id
    left join data_master msok on msok.id = t.child_id 
) 
SELECT 
  parent_id, extra_id, child_id, data_type
FROM 
  descendants where data_type ='1') abc group by parent_id,child_id

Answer 1

此查询应该有所帮助。第一个 CTE（“with”部分）提供了 table 中的所有关系。第二个CTE过滤器只结束child条记录出来。

最后一部分 - 主要查询 - 搜索 parents 将 331 作为 child 并显示给你。

with recursive result_q as (
  select 1 debug_step,  parent_data, child_data 
    from data_rel
  union all
  select debug_step + 1, q.parent_data, r.child_data
    from data_rel r
    join result_q q
      on q.child_data = r.parent_data 
),
parent_end_childs as (
  select q.parent_data, q.child_data 
    from result_q q
   where not exists (select 1 from data_rel r where r.parent_data = q.child_data)
   order by parent_data, child_data)
   
select pec.*
  from parent_end_childs pec
  join parent_end_childs pec_1
    on pec.parent_data = pec_1.parent_data
 where pec_1.child_data = 331

dbfiddle

Answer 2

您可以试试这个创建多级父子关系作为 jsonb 数组：

WITH RECURSIVE list (array_parent_child_data) AS
(
    SELECT to_jsonb(array[t.parent_data, t.child_data])
      FROM public.data_relation AS t
  UNION ALL
    SELECT t.parent_data || l.array_parent_child_data
      FROM public.data_relation AS t
     INNER JOIN list AS l
        ON l.array_parent_child_data->0 = t.child_data
       AND NOT l.array_parent_child_data @> to_jsonb(t.parent_data) -- this condition is to avoid loops
)
SELECT l2.array_parent_child_data->>0 :: integer AS parent_data
     , l2.array_parent_child_data->>-1 :: integer AS end_child_data
  FROM list AS l1
  LEFT JOIN list AS l2
    ON l1.array_parent_child_data <> l2.array_parent_child_data
   AND l1.array_parent_child_data @> l2.array_parent_child_data
 WHERE l1 IS NULL  -- l2.array_parent_child_data is not included in any l1.array_parent_child_data

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