use strict;
use DBI;

my $database='db';
my $username='user';
my $password='pass';

my $dbh=DBI->connect('DBI:mysql:database='.$database,
                     $username,$password);
print 'dbh error' if (!$dbh);

my @ref = ();
my @names = ('Jack');
my $base_sql=q{SELECT username FROM test_members WHERE referral };
while (scalar(@names)) {
  my $sql=$base_sql.($#names?'in ('.join(',',map('?',@names)).')':'=?');
  print "$sql\n";
  my $sth=$dbh->prepare($sql);
  print 'sth error' if (!$sth);
  my $rv=$sth->execute(@names);
  print 'rv error' if (!$rv);
  my $res = $sth->fetchall_arrayref();
  @names=map($res->[$_][0],0..$#$res);
  push @ref, join '|',@names if (scalar(@names));
}

print join(',',@ref),"\n";

print "finished\n";