Question

I have a table for posts and a table for categories, what i want is to select posts that are in a specific category. The problem is that the category is stored in another table and not in the posts table, here is the example:

posts

id   title       body
---------------------------
125  Some title  Blah blah

categories

postid  category
----------------
125     politic

I want in single query to fetch posts in the politic category by example, what to do?

Answer 1

Use:

SELECT p.id,
       p.title, 
       p.body
  FROM POSTS p
  JOIN CATEGORIES c ON c.postid = p.id
 WHERE c.category = 'politic'

The issue I have with your CATEGORIES table is that storing the category value as a string means the data isn’t normalized – you should instead have a CATEGORY table:

CATEGORY

• category_id (primary key, auto_increment)
• category_description

…and use the category_id value in the CATEGORIES table:

CATEGORIES

• category_id (primary key, foreign key to CATEGORY.category_id)
• post_id (primary key, foreign key to POSTS.postid)