my $db = DBI->connect( $DSN, 'user', 'sekret', {AutoCommit => 0})
    or die "Couldn't connect to database $DSN: ${\DBI->errstr}\n";
END { $db and $db->disconnect }

my $ss = $db->prepare( q{update t set department = ? where department = ?});
die unless $ss;

my $ok = 1;
REPLACE: for my $r( @order ) {
    for my $key( keys %$r ) {
        print "$key -> $r->{$key}\n";
        if( !$ss->execute( $r->{$key}, $key )) {
            warn "cannot update $key to $r->{$key}\n${\$ss->errstr}\n";
            $ok = 0;
            last REPLACE;
        }
    }
}

$ok ? $db->commit : $db->rollback;