If you don't want to define a key field, then you can't get the functionality you want. Come on, be reasonable. :)

Note that $key_field can be an arrayref, a column number, or an arrayref containing a list of column numbers:

#!/usr/bin/perl -w
use strict;
use DBI;
use Data::Dumper;
$|++;

my $dbh = DBI->connect("dbi:mysql:wordpress","username","password");
my $sth = $dbh->prepare('SELECT ID, placeName FROM wp_ajax_places WHER
+E ID <= 5');
$sth->execute;
my $h = $sth->fetchall_hashref([ 1..2 ]);

print Dumper(\$h);
[download]

$VAR1 = \{
            '4' => {
                     'Akiachak AK' => {
                                        'ID' => '4',
                                        'placeName' => 'Akiachak AK'
                                      }
                   },
            '1' => {
                     'Ester AK' => {
                                     'ID' => '1',
                                     'placeName' => 'Ester AK'
                                   }
                   },
            '3' => {
                     'Akhiok AK' => {
                                      'ID' => '3',
                                      'placeName' => 'Akhiok AK'
                                    }
                   },
            '2' => {
                     'Aguikchuk AK' => {
                                         'ID' => '2',
                                         'placeName' => 'Aguikchuk AK'
                                       }
                   },
            '5' => {
                     'Akiak AK' => {
                                     'ID' => '5',
                                     'placeName' => 'Akiak AK'
                                   }
                   }
          };
[download]

-- 
Education is not the filling of a pail, but the lighting of a fire.
 -- W. B. Yeats