Given joelba's excellent suggestion, it may also help to create some indexes to speed up subsequent searches. Recall, in "Re: Question about properly laying out a database," above:

my %cars = (
  1002 => {
    make_id => 10,
    model_id => 27,
    year => 2001,
    price => 24000,
  },
);
my %makes = {
  1 = "Chevrolet",
  10 = "Acura",
};
my %models = {
  12 = "Camaro",
  27 = "RSX",
};
[download]

For example, indexing Makes might look like:

my %makes_idx = (
  1 => [1001, ... ],    # cars that are Chevys
  10 => [1002, ...],    # cars that are Acuras
  ... );
[download]

Or, indexing Years might look like:

my %years_idx = (
  2001 => [ 1001, 1002, ... ], # cars that are 2001 models
  ... );
[download]

You get the idea.

Then searching by any single attribute that is indexed becomes nearly instantaneous. Doing a "JOIN" on two (or more) indexed attributes looks something like this:

# For example, finding all 2001 or newer Chevys
my %temp_hash = reverse %makes;         # gives the id for each make
my $make_id = $temp_hash{'Chevrolet');  # get the id for Chevy

my %make_set = map { $_=>1 } @{$makes_idx{$make_id}};  # set of cars t
+hat are Chevys

# search above for 2001 or newer models
my @temp_years = grep { $_ >= 2001 } keys %years_idx;
my @result_ids = grep { exists $make_set{$_} } @years_idx{@temp_years}
+;
[download]

Update: Changed search example to look for a range rather than a specific year.

dmm

You can give a man a fish and feed him for a day ...
Or, you can teach him to fish and feed him for a lifetime