从同一类别中获取两个slu ..

Question

通过这个查询，我从类别中获得了slug，但我希望从孩子那里得到第二个slug。

我想要这些slugs： category / sub-category / items

SELECT i.*, c.slug as cat_slug FROM items i 
LEFT JOIN cats c ON c.id = i.cat_id ORDER BY i.id;

分类表

+----------------------------------+
| id | parent_id |  name  |  slug  |
+----------------------------------+
| 1  |    0      |  Test  |  test  |
+----------------------------------+
| 2  |    1      |  Cool  |  cool  |
+----------------------------------+
| 3  |    0      |  Test5 | test5  |
+----------------------------------+

项目表

+---------------------------------+
| id | cat_id |  title  |  slug   |
+---------------------------------+
| 1  |   2    | Welcome | welcome |
+---------------------------------+
| 2  |   3    | Yeah    | yeah    |
+---------------------------------+

Answer 1

只要您对数据结构做出一些假设，特别是只有一个图层，以下查询就是实现此功能的一种方法：

SELECT i.*, c.slug, subcat.slug as cat_slug,
  concat_ws('/', c.slug, subcat.slug, i.slug) as total_slug
FROM items i 
LEFT JOIN cats c ON c.id = i.cat_id 
LEFT JOIN cats subcat on c.parent_id = subcat.id
ORDER BY i.id;

link to SQL Fiddle

这不适用于超过两个级别的类别。