my ($dbh, $field_str, $where_str, $href) = shift;

         ## instead of

   my ($dbh, $field_str, $where_str, $href) = @_;
[download]

Apologies to all. Note that the mistake does not cause compile or runtime errors. The parameters $field_str and $where_str are optional. I should have included more complete code, as the problem would probably have been spotted right away. However, the feedback was of great value and some has found its way into the current version of the code. Thanks to all who replied.

#initial stuff
#...
build_hash($dbh, '', '', $href);

sub build_hash {
   my ($dbh, $field_str, $where_str, $href) = @_; 
   my $table_str = 'table_name';
   do {
         my @fields = qw( f1 f2 f3 f4 f4 f6 f7 f8 f9 );
         $field_str = join(', ', @fields);
   } unless $field_str;

   my $query = qq( select $field_str from $table_str );
   $query .= qq( where $where_str ) if $where_str;

   my $sth = $dbh->prepare($query)
         or die "Could not prepare '$query'\n";

   $sth->execute()
         or die "Could not execute '$query'\n";

   my $ct = 0;
   while (my $tmp_href = $sth->fetchrow_hashref) {
      $ct++;
      $$href{$ct} = $tmp_href;
   }

   $sth->finish
      or die "Could not finish '$query'\n";
}
[download]