sub nick_exists {
  return $db->do( "select 1 from members where nickname="   
    . $db->quote($_[0])
  );
}

##</code><code>##

BEGIN {
my $ss = $db->prepare( 'select 1 from members where nickname=?' ) or die;

sub nick_exists {
    $ss->execute($_[0]);
    my $res = $ss->fetchrow_arrayref;
    $ss->finish;
    $res and defined $res->[0] ? 1 : 0;
}
}

##</code><code>##

use Memoize;
memoize('nick_exists');