codeigniter连接计数另一个表

     $query=$this->db->select('*')
                     ->from('activation')
                     ->join('products','products.id_pro = activation.id_pro')
                     ->join('user','user.id = products.user_p')
                     ->order_by('id_key','DESC')
                     ->get();

     return $query->result();  

I have these code where I join result from 3 tables abd that works good. What I need more is counted rows from 4.table. That table is called license, and I need to count how many rows are with id_key (primary key for table activation). How to add that in my code?

Try selecting license column as count

     $query=$this->db->select('*, COUNT(license.id_key ) as license_count')
                 ->from('activation')
                 ->join('products','products.id_pro = activation.id_pro')
                 ->join('user','user.id = products.user_p')
                 ->join('license','license.id_key = table.column?')
                 ->order_by('id_key','DESC')
                 ->get();

access the count within the object like: $query->result()->license_count;