sub create_hoh {
  my ($dbh, $table) = @_;
  my (%hoh, $count);
  my $sth = $dbh->prepare("SELECT id, last_name, first_name, address F
+ROM $table");
  $sth->execute();
    
  while (my $row_hashref = $sth->fetchrow_hashref()) {
    my $id = $row_hashref->{"id"};
    my $key = defined $id
            ? $id
            : "unknown " . $count ++;
    
    foreach my $field (keys %$row_hashref) {
      my $value = $row_hashref->{$field};
      $hoh{$key}{$field} = $value;
    }
  }
  return \%hoh;
}

sub compare_hashes {
  my ($hashref1, $hashref2) = @_;
  my %change_hash;
  foreach my $outer_key1 (sort keys %$hashref1) {
    foreach my $outer_key2 (sort keys %$hashref2) {
      if (($outer_key1 =~ /unknown/) or  
         ($outer_key2 =~ /unknown/)) {
        my $last_name1 = $hashref1->{$outer_key1}{"last_name"};
        my $last_name2 = $hashref2->{$outer_key2}{"last_name"};
        my $first_name1 = $hashref1->{$outer_key1}{"first_name"};
        my $first_name2 = $hashref2->{$outer_key2}{"first_name"};
        my $address1 = $hashref1->{$outer_key1}{"address"};
        my $address2 = $hashref2->{$outer_key2}{"address"};

        if (($last_name1 eq $last_name2) and  
            ($first_name1 eq $first_name2) and
            ($address1 eq $address2)) {
          foreach my $inner_key1 (sort keys %{$hashref1->{$outer_key1}
+}) {
            foreach my $inner_key2 (sort keys %{$hashref2->{$outer_key
+2}}) {
              if ($inner_key1 eq $inner_key2) {
                my $value1 = $hashref1->{$outer_key1}{$inner_key1};
                my $value2 = $hashref2->{$outer_key2}{$inner_key2};
                
                $change_hash{$outer_key1}{$inner_key1} = $value2
                  if (!defined $value1 and defined $value2);
              }
            }
          }
        }
        else {
          if ($outer_key1 eq $outer_key2) {
            foreach my $inner_key1 (sort keys %{$hashref1->{$outer_key
+1}}) {
              foreach my $inner_key2 (sort keys %{$hashref2->{$outer_k
+ey2}}) {
                if ($inner_key1 eq $inner_key2) {
                  my $value1 = $hashref1->{$outer_key1}{$inner_key1};
                  my $value2 = $hashref2->{$outer_key2}{$inner_key2};
                
                  $change_hash{$outer_key1}{$inner_key1} = $value2
                    if (!defined $value1 and defined $value2);
                }
              }
            }
          }
        }
      }
    }
  }
  return \%change_hash;
}
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