$sth_menu->execute();
my @vals;
while (my $ref = $sth_menu->fetchrow_arrayref()) {
    $menu{$$ref[0]} = $$ref[1];
    push @vals, $$ref[0];
    }

$cgi->popup_menu(
    -name        => 'external_database_id',
    -values        => \@vals,
    -labels        => \%menu
    );