Codeigniter. Return each category for many posts.

msearch.php

    public function get_posts($start=0)
    {
        $num = $this->get_value('numnews');
        if($num->numnews == FALSE){
            $num->numnews = 10;
        }

        return $this->db->select('post.*, GROUP_CONCAT(DISTINCT category.cat_name SEPARATOR ", ") AS categories', FALSE)
            ->join('postcat', 'post.id = postcat.postID', 'left')
            ->join('category', 'postcat.catID = category.categID', 'left')
            ->group_by('postcat.postID')
            ->order_by('post.date', 'DESC')
            ->limit((int)$num->numnews, $start)
            ->get('post')->result();
    }