my $sth = $dbh->prepare(<<'EOM');
SELECT n.id, n.name, count(*) -1 AS level
FROM foo AS n, foo AS p
WHERE n.links BETWEEN p.links AND p.rechts
GROUP BY n.links
ORDER BY n.links
EOM

$sth->execute;
my @levels;
while (my $row = $sth->fetchrow_hashref) {
    my $level = $row->{level};
    $levels[$level] = $row->{name};
    local $" = " > ";
    my @ausgabe = (@levels[0 .. $level]);
    print "@ausgabe\n";
}