my %People;
while(  my $id= GetNextId()  ) {
    my( $name, $age, $addr, $city, $state, $phone )=
      GetDataForId( $id );
    my $record=  { NAME=>$name, AGE=>$age, ADDR=>$addr,
      CITY=>$city, STATE=>$state, PHONE=>$phone };
    warn "Duplicate ID numbers: $People{ID}{$id} vs. $name\n"
      if  $People{ID}{$id};
    $People{ID}{$id}= $record;
    foreach my $field (  qw( NAME AGE STATE PHONE )  ) {
        push @{ $People{$field}{ $record->{$field} } }, $record;
    }
}
print "(The first) John Smith is ",
  "$People{NAME}{'John Smith'}[0]{AGE} years old.\n";
print "There are ",0+@{$People{AGE}{20}}, " 20-year-olds:\n";
foreach my $person (  @{ $People{AGE}{20} }  ) {
    print "\t",$person->{NAME},"\n";
}

##</code><code>##

print "(The first) John Smith is ",
  "$People{ByNAME}{'John Smith'}[0]{AGE} years old.\n";

##</code><code>##

my $byID= $People{ID};
foreach my $person (  @$byID  ) {
}