my $b;
   my $sql   = qq{SELECT b FROM blah WHERE user = ?};
   my $sth   = $dbh->prepare("$sql");
      $sth  -> execute('bahbah');
      $sth  -> bind_col(1,\$b);
   while( $sth->fetch ) {
      print "$b\n";
   }
   ################
   # OR:
   ################
   my $sql   = qq{SELECT b FROM blah WHERE user = ?};
   my $sth   = $dbh->prepare("$sql");
      $sth  -> execute('bahbah');
   my $rows  = [];    # cache for batches of rows
   while(my $row = shift(@$rows) 
                || shift(@{$rows=$sth->fetchall_arrayref([0],10_000)||[]})) {
      print "$row->[0]\n";
   }