Mysql - 一对多的单一查询

Question

I have a table named posts and another table named attachments ...

A post can have many attachments ...

So, I create a middle table called post_attachment ..

How to get the list of posts data including the attachments data in A SINGLE QUERY ?

..

Please refer below to make it clearer to understand...

---

Below are the table structure:

-

posts table have 4 columns:

1. id
2. title
3. body_text

-

attachments table have 3 columns:

1. id
2. filename
3. file_url

-

post_attachment table have 2 columns:

1. post_id
2. file_id

---

Below are the example of a post that have multiple attachments

posts table:

-

attachments table:

-

post_-attachment table:

In the example above, it tells the post (ID: 1) has 3 attachments which is ID: 1,2 and 3.

So, the question is How to GET the list of posts which will have columns posts.title , attachments.filename , attachments.file_url in A SINGLE QUERY ?

Answer 1

You must join the 3 tables:

select
  p.*, a.*
from post p
left join post_attachment pa on pa.post_id = p.id
left join attachments a on a.id = pa.file_id

The LEFT JOIN is needed in case a post does not have any attachments.