Comment system not working.

Can you share you comments and posts table structure;

Also there are mistakes in your get comments query:
Instead of 
       $this->db->select('*');
        $this->db->from('comments');
        $this->db->where('comments', array('slug' => $slug));
        $this->db->join('comments', 'comments.id = posts.id');
change to 
        $this->db->select('*');
        $this->db->from('comments');
        $this->db->join('comments', 'comments.id = posts.id');
        $this->db->where(array('slug' => $slug));
        $query = $this->db->get();

where clause comes after join;

and what is "posts.id" in your query?
        

This is my POSTS table in DB:


This is my COMMENTS table in database:


and this is my full code to "get" the comments for each post(Post_model).

PHP Code:

// Comments
    public function get_post_comments($slug){
        $this->db->select('username,email,website,body');
        $this->db->from('comments');
        $this->db->join('comments', 'comments.id = posts.id');
        $this->db->where(array('slug' => $slug));
        $query = $this->db->get();
        
        if($query->num_rows() >= 1){
            return $query->result();
        } else {
            return false;
        }
    } 


I do Front-End development most of the time