Question

I have a table categories and table posts . I want to return categories that have more than 3 posts.

My query

SELECT `categories`.`category_title`, COUNT(posts.post_id) as total_posts 
FROM (`categories`) 
JOIN `posts` ON `posts`.`category_id` = `categories`.`category_id` 
HAVING `total_posts` > 3 
ORDER BY `categories`.`date_created` desc

it returns just 1 row.. What is the correct way to do this type of query without using 2 queries?

Answer 1

Your query is making use of a MySQL feature called “hidden columns” and you might not even know it. This is because your query is referencing elements, such as date_created, which should be aggregated but are not (“should” here means according to the SQL standard and most other databases).

The problem with your query is that it is missing the group by. An alternative way of writing this is with the aggregation in a subquery, before joining to category:

SELECT `categories`.`category_title`, total_posts 
FROM `categories` JOIN
     (select categoryid, COUNT(posts.post_id) as total_posts
      from `posts`
      group by categoryid
      having count(*) > 3
     ) pc
     ON `pc`.`category_id` = `categories`.`category_id`
ORDER BY `categories`.`date_created` desc