Sounds like what you need to do is use a hash: 

# build a hash with son => father as key => value pairs
my %sons;
while(<DATA>) {
    chomp;
  next unless $_;
    my ($son, $father) = split /\s+/, $_;
    $sons{$son} = $father;
}

# make another hash keyed on the fathers that includes all their sons
my %fathers;
for my $son ( keys %sons ) {
    # find the father or $son from out %sons hash
    my $father = $sons{$son};
    push @{$fathers{$father}}, $son;
}

# show the results:
print "Son\tFather\n";
for my $son ( keys %sons ) {
    print $son, "\t", $sons{$son}, "\n";
}

print "\n\nFather\tSon(s)\n";
for my $father ( keys %fathers ) {
    my @sons = @{$fathers{$father}};
    my $sons = join " | ", @sons;
    print $father, "\t\t", $sons, "\n";
}

__DATA__
1   1
2   2
3   3
4   1
5   3
6   4
7   5
8   1
9   2

[download]

This will give you the following (which I presume is along the lines of what you are trying to do. 

Son    Father
1    1
2    2
3    3
4    1
5    3
6    4
7    5
8    1
9    2


Father    Son(s)
1        1 | 4 | 8
2        2 | 9
3        3 | 5
4        6
5        7

[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

In reply to Re: Correction to Database problem by tachyon
in thread Correction to Database problem by nasa

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