カラム名一覧取得
application/core/MY_Model.phpとかに追記
public function get_column_names($table = '', $format = '%s')
{
    $names = $this->db->list_fields(empty($table) ? $this->name : $table);
    if(!empty($format)){
        foreach($names as &$name){
            $name = sprintf($format,$name);
        }
    }
    return $names;
}