use DBI;
my($main,$password,$nick);

my $db_name = "DBI:mysql:users"; ## den Datenbankname ersetzen
my $db_user = "root"; ## Benutzername
my $db_pass = ""; ## Passwort
my @ergebnis;
my $test;

my $dbh = DBI->connect("$db_name","$db_user","$db_pass") || die "Database connection not made: $DBI::errstr";
my $sql_insert = qq{insert into  mitglieder (password,nick) values (?,?)};
my $sql_select = qq~SELECT * FROM user WHERE password = ? AND nick = ?~;
my $sql_update = qq~UPDATE user SET password = ? WHERE nick = ?~;
my $sth = $dbh->prepare($sql_select) or die $dbh->errstr();    
$sth->execute($password,$nick) or die $dbh->errstr();
if($sth->fetchrow_array()){
  $sth = $dbh->prepare($sql_update) or die $dbh->errstr();
  $sth->execute($password,$nick);
}
else{
  $sth = $dbh->prepare($sql_insert) or die $dbh->errstr();
  $sth->execute($password,$nick) or die $dbh->errstr();
}