my $sth = $dbh->prepare(q{
    UPDATE DGKTO_BASIS
    SET SVT_BEITRAGSKONTONUMMER = '00000000099'
    WHERE VERSICHERUNGSTRAEGERCODE = '04' and DIENSTGEBERKONTONUMMER = '00000015'})
    || die "Can't prepare statement: $DBI::errstr";

C:\mist>perl mist.pl
DBD::Oracle::st execute failed: ORA-01401: inserted value too large for column (
DBD: oexec error) at mist.pl line 27.

my $sth = $dbh->prepare(q{
    UPDATE DGKTO_BASIS
    SET SVT_BEITRAGSKONTONUMMER = ?
    WHERE VERSICHERUNGSTRAEGERCODE = ? and DIENSTGEBERKONTONUMMER = ?})
    || die "Can't prepare statement: $DBI::errstr";

my $upd  = "0000000100"; # Achtung auf die Länge!!
my $key1 = "04";
my $key2 = "00000015";

$sth->execute($upd, $key1, $key2) or die $dbh->errstr;