If you just want to see whether a value appears in a column of a table, performing a count(*) is a fearfully expensive way of going about that. At the worst, you will perform a full table scan.

The query would be better formulated as select 1 from members where nickname='...'

If this is just a once-off, the simplest approach would be to use the do method, with something (error-checking notwithstanding) like:

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

If, on the other hand, you know you'll be pounding on this routine in an inner loop, it might then be worthwhile recasting it as a prepared statement:

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

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

The beauty of this approach is that you don't have to change your code. The access to the database is abstracted away in the nick_exists routine.

And as if that wasn't enough, you could further add

use Memoize;
memoize('nick_exists');
[download]

... although you want to be careful with that. The program will continue to assume that a nick that has just been taken is still available. That would be a bug. But, used with care, this can provide a healthy speed boost.