postgresql - 如何从邻接表中获取后代数组？

Question

我有下表和数据

CREATE TABLE relationships (a TEXT, b TEXT);
CREATE TABLE nodes(n TEXT);
INSERT INTO relationships(a, b) VALUES 
 ('1', '2'), 
 ('1', '3'),
 ('1', '4'),
 ('1', '5'),
 ('2', '6'),
 ('2', '7'),
 ('2', '8'),
 ('3', '9');
INSERT INTO nodes(n) VALUES ('1'), ('2'), ('3'), ('4'), ('5'), ('6'), ('7'), ('8'), ('9'), ('10');

我要输出

  n  |  children
  1  |  ['2', '3', '4', '5', '6', '7', '8', '9']
  2  |  ['6', '7', '8', '9']
  3  |  ['9']
  4  |  []
  5  |  []
  6  |  []
  7  |  []
  8  |  []
  9  |  []
  10 |  []

我正在尝试使用 WITH RECURSIVE，但在如何将参数传递给 CTE 上遇到困难

WITH RECURSIVE traverse(n) AS (
    SELECT *
    FROM relationships
    WHERE a = n --- not sure how to pass data to here
    UNION ALL
    ...
)
WITH basic_cte AS (
    SELECT a1.n as n,
           (SELECT COALESCE(json_agg(temp), '[]')
            FROM (
                         (SELECT * FROM traverse(a1.a))
                 ) as temp
           ) as children
    FROM nodes as a1
)
SELECT *
FROM basic_cte;

Answer 1

要获取所有节点的子节点列表，您需要对节点表进行左连接

with recursive rels as (
  select a,b, a as root
  from relationships
  union all
  select c.*, r.root
  from relationships c
    join rels r on r.b = c.a
)
select n.n, array_agg(r.b) filter (where r.b is not null)
from nodes n
  left join rels r on r.root = n.n
group by n.n
order by n.n;