my $upd = $dbh->prepare("UPDATE new_entrant SET forename=?,surname=? WHERE emp_no=?") or die $DBI::errstr;
while (my $row = $sth->fetch) {
    $upd->execute($wrk_forename, $wrk_surname, $wrk_emp_no) or die $DBI::errstr;
}
$upd->finish();