Question

Right so, I’m not particularly skilled at this at all, this is in fact my first join query, so be gentle. I’m going to give as much detail as I possible can as it’s probably going to hit most of you in face like a frying pan, but it’s doing my nut in!

I’m having issues with a query for a blog i’m trying to write in codeigniter. I had set up a query with 2 joins for posts and it’s categorys using three tables: posts, categories and posts_categories now i’m trying to join my comments table too, to do a count.

This is the code in my model that displays both the generic posts i’ve made up:

            $this->db->select('posts.id,
                            posts.title,
                            posts.slug,
                            posts.content,
                            posts.author,
                            posts.date,
                            posts.time,
                            posts.tags,
                            posts.status,
                            GROUP_CONCAT(categories.name SEPARATOR \'-\') AS categories
                            ');
        $this->db->group_by(array('posts.id'));
        $this->db->from('posts');
        $this->db->join('posts_categories', 'posts_categories.blog_entry_id = posts.id');
        $this->db->join('categories', 'posts_categories.blog_category_id = categories.category_id');
        $query = $this->db->get();
        return $query->result_array();

this is the result:

(
[0] => Array
    (
        [id] => 1
        [title] => My first blog post!
        [slug] => my-first-blog-post
        [content] => This is my first blog post. Don't worry, it's just a test, my real blog won't be this boring, hopefully!
        [author] => Joni
        [date] => 2012-01-23
        [time] => 00:00:00
        [tags] => Testing
        [status] => 
        [categories] => Testing-More Tests-Test
    )

[1] => Array
    (
        [id] => 2
        [title] => This is another test-post
        [slug] => this-is-another-test-post
        [content] => Well you guessed it. another boring test post, enjoy!
        [author] => Joni
        [date] => 2012-01-23
        [time] => 00:00:00
        [tags] => Sexy
        [status] => 
        [categories] => Test
    )

)

Now when i modify the query to implement the third join for comments like so:

            $this->db->select('posts.id,
                            posts.title,
                            posts.slug,
                            posts.content,
                            posts.author,
                            posts.date,
                            posts.time,
                            posts.tags,
                            posts.status,
                            GROUP_CONCAT(categories.name SEPARATOR \'-\') AS categories,
                            count(comments.id) as total_comments
                            ');
        $this->db->group_by(array('posts.id'));
        $this->db->from('posts');
        $this->db->join('posts_categories', 'posts_categories.blog_entry_id = posts.id');
        $this->db->join('categories', 'posts_categories.blog_category_id = categories.category_id');
        $this->db->join('comments', 'comments.post_id = posts.id');
        $query = $this->db->get();
        return $query->result_array();

I end up with this

(
[0] => Array
    (
        [id] => 1
        [title] => My first blog post!
        [slug] => my-first-blog-post
        [content] => This is my first blog post. Don't worry, it's just a test, my real blog won't be this boring, hopefully!
        [author] => Joni
        [date] => 2012-01-23
        [time] => 00:00:00
        [tags] => Testing
        [status] => 
        [categories] => Testing-More Tests-Test
        [total_comments] => 3
    )

)

If you’ve made it this far, sorry it’s so long, and just wanna say thanks in advance!

cheers joni

Answer 1

You need to be using a LEFT OUTER JOIN otherwise you’ll only get posts that have comments. When you do an INNER JOIN (the default), it will require that whatever is on the left have a matching element on the right side of the join. If it doesn’t find a match on the right side, it omits it. A LEFT OUTER JOIN will keep all of the elements on the left side of the join regardless of whether there is a match on the right side.

Change this:

$this->db->join('comments', 'comments.post_id = posts.id'); 

to

$this->db->join('comments', 'comments.post_id = posts.id', 'left outer' );