# query setup omitted.

# @keys is an array of your primary keys. The
# first element of the array is the key used in
# %tableData. Each following key is used to
# identify a nested hash.

my $last_key = pop @keys;
my %tableData;

while (my @data = $dbh -> dbnextrow)
  {
     my $row = { };

     my $i = 0;
     foreach my $value (@data) {
       $value =~ s/^\s+//;
       $value =~ s/\s+$//;
       $row->{$columnames[$i++]} = $value;
     }

     my $nest = \%tableData;
     my $key_value;

     foreach my $key_name (@keys) {
       $key_value = delete $row->{$key_name};
       $nest = ($nest->{$key_value}) ? ($nest->{$key_value})
                                     : ($nest->{$key_value} = { });
     }

     $key_value = delete $row->{$last_key};
     $nest->{$key_value} = $row;
  }

return \%tableData;