sub quote_number {
    my($dbh, $value) = @_;
    if (defined $value) {
      # force to number
      return $value + 0;
    } else {
      return $dbh->quote($value);
    }
  }

##</code><code>##

  sub quote_integer {
    my($dbh, $value) = @_;
    if (defined $value) {
      # pattern approach
      die "Not an integer" unless $value =~ /^[-+]?\d+\z/;
      # maths approach
      die "Not an integer" unless $value == int($value);
      return $value + 0;
    } else {
      return $dbh->quote($value);
    }
  }