...
   $sth->execute($objid);
   my @rows = @{$sth->fetchall_arrayref()};
   $sth->finish();
   foreach $row (@rows) {
   ...

##</code><code>##

Sub GetChildren{
   my ($objid) = @_;

   my $sth = $dbh->prepare(<<'   ;');
      SELECT objid, type
        FROM table
       WHERE parentid=?
   ;

   # Initial fetch.
   $sth->execute($objid);
   @rows = @{$sth->fetchall_arrayref()};

   while (@rows) {
      my ($objid, $type) = @{shift(@rows)};

      if ($type eq "Container") {
         # Add to todo list.
         $sth->execute($objid);
         push(@rows, @{$sth->fetchall_arrayref()});
         next;
      }

      do something else
   }

   $sth->finish();
}