my $data = $dbh->selectall_arrayref(
	'SELECT ID, NUM FROM INDEX WHERE ID LIKE F% OR ID LIKE G%',
	{ Columns => {} }
);

my %index;
foreach (@{ $data }) {
	if ($_->{'ID'} eq 'G') {
		$index{$_->{'NUM'}} = -1;
	} else {
		$index{$_->{'NUM'}} = 1 if (not exists $index{$_->{'NUM'}});
	}
}

my @index;
foreach (keys %index) {
	push @index, 'F' . $_ if ($index{$_} == 1);
}

print join("\n", @index), "\n";