protected function addParam($column, $value)
    {
        if (is_array($value)) {
            $this->params = array_merge($this->params, $value);
            $this->param_columns = array_merge($this->param_columns, array_fill(0, count($value), $column));
            return;
        }
        $this->params[] = $value;
        $this->param_columns[] = $column;
    }