Solved it I think:

use strict;

use Tie::IxHash;


my %login;

{
tie( my %csv, 'Tie::IxHash',

  'one'   => undef,
  'two'   => undef,
  'three' => undef,
  'four' => undef,
  'five' => undef,
  );
  $csv{one} = "11";
  $csv{two} = "12";
  $csv{three} = "13";
  $csv{four} = "14";
  $csv{five} = "15";

  $login{1} = \%csv;
}

{
tie( my %csv, 'Tie::IxHash',

  'one'   => undef,
  'two'   => undef,
  'three' => undef,
  'four' => undef,
  'five' => undef,
  );
  $csv{one} = "11";
  $csv{three} = "23";
  $csv{four} = "14";
  $csv{five} = "25";

  $login{2} = \%csv;
}

{
tie( my %csv, 'Tie::IxHash',

  'one'   => undef,
  'two'   => undef,
  'three' => undef,
  'four' => undef,
  'five' => undef,
  );  

  $csv{one} = "31";
  $csv{two} = "12";
  $csv{three} = "23";
  $csv{five} = "25";
  
  my $match = "2";

  while (my ($k,$v) = each %login) {
      if ($k eq $match) {
        my %union;
        print "MATCH\n";
        while ( my ($k, $v) = each %$v ) { $union{$k} = $v; }
        while ( my ($k, $v) = each %csv ) { $union{$k} = $v; }
        print map{$_ ."=". $union{$_} ."\n"} keys %union;
      } else {
        print "NO MATCH\n";
        while ( my ($k, $v) = each %$v ) { print $k ."=". $v."\n"; }
      }
        
  }
}
[download]

Mhh the union part doesn't work like i want to. Empty elements in it?
Off course suggestions howto improve the rest of the code are also welcome!!

--
My opinions may have changed,
but not the fact that I am right