my $stmt = 'SELECT Tabelle1.ID,Tabelle1.NEID , Tabelle2.REfID,Tabelle2.NEID AS NEID2 From Tabelle1 Left JOIN On Tabelle1.ID = Tabelle2.REfID';
my $sth = $dbh->prepare($stmt) or die $dbh->errstr();
$sth->execute() or die $dbh->errstr();

while(my ($id,$neid_1,$refid,$neid_2) = $sth->fetchrow_array()){
    if($newdata->{NEID} eq $neid_1){
        print "gleich!\n";
    }
}