my %hUsers;

#find all unique combinations of user and product
while(my @row = $res->fetchrow_array()) {
  my ($username, $product) = @row;
  $hUsers->{$username}{$product} = 1;
}

# print product counts per user
foreach $user_name (sort keys %$hUsers) {
  print $user_name, ' ', scalar keys $hUsers{$user_name}, "\n";
}