Question

我正在尝试获取并显示基于product_id的所有parent_id名称。我正在做的是创建一个管理页面，我可以在其中添加特定产品的类别，但首先我需要在与parent_id相关联的categories表中获取每个名称，然后才能添加/编辑它们。

所以当我查询product_id 99时，我应该回来：滑板 - ＆gt; action_sports - ＆gt;运动

 Categories Table
 ----------------------------------
 | id |     name      | parent_id |
 ----------------------------------
 | 1  |    sports     |    null   |
 ----------------------------------
 | 2  | action_sports |     1     |
 ----------------------------------
 | 3  | skateboarding |     2     |
 ----------------------------------


 Product Category Joiner Table
 ----------------------------
 | product_id | category_id |
 ----------------------------
 |     99     |      3      |
 ----------------------------

我唯一能想到的是加入表格。我希望能够在不同的id上两次加入同一个表，但这显然不起作用。

 SELECT categories.name, categories.parent_id FROM products 
 INNER JOIN product_category ON products.id = product_category.product_id
 INNER JOIN categories ON categories.id = product_category.category_id
 WHERE products.id = 99

 returns:

 -----------------------------
 |      name     | parent_id |
 -----------------------------
 | skateboarding |     2     |  <-- need to get name of each parent_id above
 -----------------------------

有什么想法吗？希望我已经解释得足以让它有点意义

Answer 1

您可以使用递归CTE，但首先是类别，但仅限于需要的类别：

with recursive cte as (
      select c.id, c.name, c.parent_id
      from products p join
           categories c
           on c.id = p.category_id
      where p.product_id = 99
      union all
      select c.id, c.name, p.parent_id
      from cte join
           products p
           on cte.parent = c.id
     )
select *
from cte;

Answer 2

如果您不知道有多少级别可以访问parent_id null，您可以使用递归cte来解决此问题。

with recursive cte as
  (select p.id as product_id,
          c.name,
          c.parent_id
   from products p
   join product_category pc on p.id = pc.product_id
   join categories c on c.id = pc.category_id
   union all
   select p.id,
          c.name,
          c.parent_id
   from cte r
   join products p on p.id = r.product_id
   join categories c on c.id = r.parent_id
  )
select *
from cte
where product_id=99 --change this to the desired product_id

SQL类别 - 无法获取所有parent_id名称

2 个答案: