my %myhash;
build_hash(\%myhash);
print Dumper(\%myhash);  ## shows %myhash to be empty

sub build_hash {
   my $href = shift;
   my %results;
   my $sth = $dbh->prepare( $query );
   $sth->execute();
   my $ct = 0;
   while (my $tmp_href = $sth->fetchrow_hashref) {
      $ct++;
      $results{$ct} = $tmp_href;
   }
   %{ $href } = %results;
   ## also tried Storable's dclone(), but same results
   ## $href = dclone(\%results);
   print Dumper($href); ## prints desired results
}