SQL - Select all posts with comma separated values of categories with relations table between posts and categories

Question

I wish to select the posts with the name of the categories with comma separated values like so:

posts table

id	post_name	post_content
1	first post	first post content
2	second post	second post content
3	third post	third post content

relations table

relation_id	post_id	cat_id
1	1	1
2	1	4
3	1	5
4	2	4
5	2	5
6	3	2
7	3	3

categories table

cat_id	cat_name	cat_slug	cat_desc
1	Cat One	catone	lorem ipsum one
2	Cat Two	cattwo	lorem ipsum two
3	Cat Three	catthree	lorem ipsum Three
4	Cat Four	catfour	lorem ipsum Four
5	Cat Five	catfive	lorem ipsum Five

Result:

id	post_name	post_content	cat_slug	cat_name
1	first post	first post content	catone,catfour,catfive	Cat One, Cat Four, Cat Five
2	second post	second post content	catfour,catfive	Cat Four, Cat Five
3	third post	third post content	cattwo,catthree	Cat Two, Cat Three

I've tried group contact with no luck, its working with multiple queries and foreach loop, but I want to know if its possible to achieve this with only one query.

Answer 1

Did you try a join and group by ?

select p.*,
       group_concat(pc.cat_slug) as cat_slugs,
       group_concat(pc.cat_name) as cat_names
from posts p left join
     relations r
     on r.post_id = p.id left join
     post_categories pc
     on pc.cat_id = r.cat_id
group by p.id;

Answer 2

This works like a charm in my case. I also have 2 tables and 1 relation table just like yours. (MSSQL)

SELECT
     p.*
    ,STUFF((
          SELECT ',' + c.cat_name
          FROM categories c
          JOIN relations r ON r.post_id=p.id
          WHERE r.cat_id= c.cat_id
          FOR XML PATH('')), 1, 1, '') as Result
FROM posts p