MySQL: Selecting an entry's parent and grandparent names - mysql

Question

On my site, I have several articles, and each article is assigned to a location with a category. This is how it has been set up for quite some time, so I can't change how it works.
The relationship between these is set in two tables, categories and category_posts:
categories
+--------+------------------+------------------+-----------+
| cat_id | cat_name | cat_url_title | parent_id |
+--------+------------------+------------------+-----------+
| 1 | Toronto | toronto | 2 |
| 2 | Ontario | ontario | 3 |
| 3 | Canada | canada | 0 |
| 4 | Vancouver | vancouver | 5 |
| 5 | British Columbia | british_columbia | 3 |
| 6 | Montreal | montreal | 7 |
| 7 | Quebec | quebec | 3 |
| 8 | San Francisco | san_francisco | 9 |
| 9 | California | california | 10 |
| 10 | United States | united_states | 0 |
+--------+------------------+------------------+-----------+
category_posts
+----------+--------+
| entry_id | cat_id |
+----------+--------+
| 990 | 1 |
| 991 | 4 |
| 992 | 8 |
| 993 | 6 |
| 994 | 4 |
| 995 | 4 |
| 996 | 1 |
| 997 | 6 |
| 998 | 8 |
| 999 | 4 |
| 1000 | 3 |
| 10001 | 10 |
+----------+--------+
So category posts contains a list of all the articles' entry id's, and which category they have been assigned. Then the categories table lists all the categories, including their parents and their URL titles.
What I'm trying to do is write a query that for any article entry id, returns its category name and url title, as well of those of its parents and grandparents.
So for example, if I used 999 as the entry id, this is the result I would want:
+-----------+---------------+------------------+------------------+------------------+-----------------------+
| cat_name | cat_url_title | parent_name | parent_url_title | grandparent_name | grandparent_url_title |
+-----------+---------------+------------------+------------------+------------------+-----------------------+
| Vancouver | vancouver | British Columbia | british_columbia | Canada | canada |
+-----------+---------------+------------------+------------------+------------------+-----------------------+
Now, I'm kind of stuck with writing a query to do that. I know how to get just the entry's own category name and url title using this query:
SELECT cat_name, cat_url_title FROM categories
JOIN category_posts
ON categories.cat_id=category_posts.cat_id
WHERE category_posts.entry_id = 999;
But how would I include the parent and grandparent categories? Hopefully that makes sense.
EDIT: I just realized a modification is necessary. I can't be certain that only child categories will be selected as the category for every article. Parent and even grandparent categories could also be selected. When I put the such an article's entry id into the query, it returns with no results. I updated the category_posts table to show this. Does anyone know how I can do this?

Answer 1

you can join three instances of your categories table to get that:
SELECT
child.cat_name as child_cat_name, child.cat_url_title as child_cat_url_title,
parent.cat_name as parent_cat_name, parent.cat_url_title as parent_cat_url_title,
grandparent.cat_name as grandparent_cat_name, grandparent.cat_url_title as grandparent_cat_url_title
FROM categories as child
JOIN category_posts ON child.cat_id=category_posts.cat_id
JOIN categories as parent on child.parent_id = parent.cat_id
JOIN categories as grandparent on parent.parent_id = grandparent.cat_id
WHERE category_posts.entry_id = 999;

Answer 2

SELECT
c1.cat_name,
c1.cat_url_title,
c2.cat_name AS parent_name,
c2.cat_url AS parent_url_title,
c3.cat_name AS grandparent_name,
c3.cat_url AS grandparent_url_title
FROM categories c1
INNER JOIN categories c2 ON (c1.parent_id = c2.cat_id)
INNER JOIN categories c3 ON (c2.parent_id = c3.cat_id)
INNER JOIN category_posts p ON (c1.cat_id = p.cat_id)
WHERE p.entry_id = 999;

Answer 3

Please try this :
select c.cat_name,c.cat_url_title,
b.cat_name as cat_name_parent,b.cat_url_title as cat_url_title_parent,
a.cat_name as cat_name_grandparent,a.cat_url_title as cat_url_title_grandparent
from categories a
inner join categories b on b.parent_id = a.cat_id
inner join categories c on c.parent_id = b.cat_id
inner join category_posts d on c.cat_id = d.cat_id and d.entry_id = '999'