如何在多个表上设置外键/查询

Question

I'm trying to setup a database for a blog, it has the following tables:

posts (
   id,
   author_id,
   category_id,
)
authors (
   id,
)
categories (
   id,
)
tags (
  id
)
comments (
 id
)
comments_to_posts (
  comment_id,
  post_id,
)
tags_to_posts (
  tag_id,
  post_id,
)

The basic idea is this:

 many-to-1 tags-to-posts / 1-to-many posts-to-tags
 1-to-many authors-to-posts / 1-to-1 posts-to-authors
 1-to-many categories-to-posts / 1-to-1 posts-to-categories
 1-to-1 comments-to-posts / 1-to-many posts-to-comments

1. I'm not sure which tables I should be putting the foreign keys on etc... I've been experimenting trying different combinations but I'm unsure where exactly they should be set.

2. I would like to be able to to query the posts table and get all the tags, the author, the category and comments in a single query. An example would be good.

NB I don't have any issues with syntax, this is more logistics than anything else, pseudo-code would be fine.

Answer 1

Your tables should look like this:

posts ( 
   id, 
   author_id, 
   category_id, 
   message 
) 

comments ( 
   id, 
   post_id, 
   message
)

authors ( 
   id, name
) 

categories ( 
   id, name   
) 

tags ( 
   id, tag 
) 

tags_to_posts ( 
   tag_id, 
   post_id 
)

And here is the mysql query to get all the data you want:

SELECT
   posts.id,
   tags.id,
   posts.message,
   comments.message AS comment,
   tags.tag,
   categories.name AS categorie,
   authors.name AS author
FROM posts
JOIN tags_to_posts ON posts.id = tags_to_posts.post_id
JOIN comments ON posts.id = comments.post_id
JOIN tags ON tags.id = tags_to_posts.tag_id 
JOIN categories ON categories.id = posts.category_id
JOIN authors ON authors.id = posts.author_id;