# SQL
#SELECT DISTINCT date FROM hit WHERE location_id = $loc_id
# will get a list back in the form 'YYYY-MM-DD'
my %months;

while (my $row = $sth->fetchrow) {
 my ($year, $month, $day) = split '-', $row;
 push @{$months{"$month-$year"}}, $day;
}

# cheap print routine to illustrate access to the hash

foreach my $month (keys %months) {
    print "For the month of $month, we have events on the following days :\n";
    print "$_ " foreach (@{$months{$month}});
    print "\n";
}