my $sth = $dbh->prepare($query);
$sth->execute();

my $current_month;
my $current_group;
my $current_person;

while (my $rv = $sth->fetchrow_arrayref());
   if ($rv[0] ne $current_monthkey) {
      # print out new month header
      $current_month = $rv[0];
      undef $current_group;
      undef $current_person;
   }
   if ($rv[1] ne $current_group) {
      # print out new group header
      $current_group = $rv[0];
      undef $current_person;
   }
   if ($rv[2] ne $current_person) {
      # print out new person header
      $current_person = $rv[1];
   }
   # print out stat
}

$sth->finish();
$dbh->disconnect();