public function where($field, $value, $not = false)
    {
        $reserverd_word = $this->with_where ? 'AND' : 'WHERE';
        $operator = $not ? '!=' : '=';
        $this->query .= "{$reserverd_word} {$field} {$operator} '{$value}'";
        $this->with_where = true;

        return $this;
    }