SQL - 使用帖子和类别之间的关系表选择所有类别的逗号分隔值的帖子

Question

我希望选择带有逗号分隔值的类别名称的帖子，如下所示：

帖子表

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

关系表

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

分类表

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

结果：

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

我尝试了组联系，但没有成功，它可以处理多个查询和 foreach 循环，但我想知道是否有可能只用一个查询来实现。

Answer 1

你试过join和group by吗？

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;