#!/usr/bin/perl

use strict;
use warnings;

my @pairs_in_db = ([1,2],[1,9],[3,4],[5,6]);
my @pairs_from_somewhere_else = ([1,2],[5,6],[7,18]);

#prepare map
my %map;
# set original and a counter
$map{join(',',@$_)}=[$_,0] for(@pairs_in_db);

for(@pairs_from_somewhere_else)
{
  my $str=join(',',@$_);
  if(exists($map{$str}))
  {
    $map{$str}->[1]++;
    printf("<%02u, %02u> was in db\n", @{$map{$str}->[0]});
  }
  else
  {
    printf("<%02u, %02u> has to be inserted into the databse\n", @$_);
  }
}

for(values(%map))
{
  unless($_->[1])
  {
    printf("<%02u, %02u> will be removed\n", @{$_->[0]});
  }
}