Here's my refactoring of chayashida's fine illustration:

#!perl

use strict;
use warnings;

my @all_queries; # Array of hashes
my %queries_by;  # Hash of arrays

push @all_queries, { foo => 20 };
push @all_queries, { bar => 30 };
push @all_queries, { foo => 10 };
push @all_queries, { zen => 90 };
push @all_queries, { zen =>  1 };

for my $query (@all_queries) {
    my ($query_key, $query_value) = %$query;

    push @{ $queries_by{$query_key} }, $query_value;
}

for my $query_key (sort keys %queries_by) {
    my @query_values = sort { $a <=> $b } @{ $queries_by{$query_key} }
+;
    my $query_values = join ',', @query_values;

    print "$query_key has $query_values\n";
}

__END__
bar has 30
foo has 10,20
zen has 1,90
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