use CGI;
use DBI;

sub update_mytable($$$$$) {
  my ($db,$id,$name,$rank,$serialno)=@_;

  # Use late binding, good practice for some DBs; doesn't hurt others
  my $sql = "update mytable set name = ?, rank = ?, serialno =? where id= ?";
  my $sth;

  # Wrap db activities in eval so non-fatal
  eval($sth = $db->prepare($sql) );
  eval( $sth->execute($name,$rank,$serialno,$id); ) unless $@;

  # 
  return $@?$@:1;
}

my $q = new CGI;
my $d = new DBI(....);
my $id = $q->param('id');
...
my $serialno = $q->param('serialno');
update_mystable($d,$id,$name,$rank,$serialno);