Postgresql 组从递归查询中检索到的记录，这些记录具有相同的父级、祖级和父级

我有一个表，表中的项比与类别的关系要多

项目

项目类别

id | category_id | item_id
  1     4            1
  2     5            1
  3     7            1
  4     8            1

类别（父项id自身的外键）

我试图从子项到父项获取项目类别，因此我使用：

 WITH RECURSIVE descendants(name, id, slug, parent_id, bread_order) AS (
 SELECT  name, id, slug, parent_id, 0
 FROM categories
 where id in (
 SELECT c.id FROM items AS p
 INNER JOIN items_categories AS pc ON p.id=pc.item_id 
 INNER JOIN categories AS c ON pc.category_id = c.id
     WHERE p.id = 10
 )   
 UNION ALL
 SELECT c2.name, c2.id, c2.slug, c2.parent_id, bread_order+1
 FROM categories AS c2
 INNER JOIN descendants AS d ON c2.id=d.parent_id
) SELECT id, name, parent_id, bread_order FROM descendants 
ORDER by bread_order DESC

问题是两个子类别可以有相同的父类别，或者一个类别的父类别是另一个类别的父类别

C1 -> B1 -> A1
C2 ->B1  -> A1
C3 ->B2  -> A1
DE -> D1 -> A1
DT  -> A1

我尝试将它们分组，但是，因为有相同的父母，grand_父母不是我需要的，当我从数据库检索信息时，我需要知道如何创建路径（见上文）

---

是否有任何方法，比如将CASE与子查询返回的ID一起使用？

您可以在查询期间聚合路径：

WITH RECURSIVE descendants(name, id, parent_id, bread_order, path) AS (
  SELECT  name, id, parent_id, 0, array[id] as path
  FROM categories
  where id in (SELECT c.id
               FROM items AS p
                 JOIN items_categories AS pc ON p.id=pc.item_id 
                 JOIN categories AS c ON pc.category_id = c.id
               WHERE p.id = 1)   
  UNION ALL

  SELECT c2.name, c2.id, c2.parent_id, bread_order+1, d.path||c2.id
  FROM categories AS c2
    JOIN descendants AS d ON c2.id=d.parent_id
) 
SELECT id, name, parent_id, path, bread_order
FROM descendants 
ORDER by path

---

可以，使用路径唯一的问题是正确的路径位于顶部父级，而不是起始子级

C1 -> B1 -> A1
C2 ->B1  -> A1
C3 ->B2  -> A1
DE -> D1 -> A1
DT  -> A1

WITH RECURSIVE descendants(name, id, parent_id, bread_order, path) AS (
  SELECT  name, id, parent_id, 0, array[id] as path
  FROM categories
  where id in (SELECT c.id
               FROM items AS p
                 JOIN items_categories AS pc ON p.id=pc.item_id 
                 JOIN categories AS c ON pc.category_id = c.id
               WHERE p.id = 1)   
  UNION ALL

  SELECT c2.name, c2.id, c2.parent_id, bread_order+1, d.path||c2.id
  FROM categories AS c2
    JOIN descendants AS d ON c2.id=d.parent_id
) 
SELECT id, name, parent_id, path, bread_order
FROM descendants 
ORDER by path