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<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <meta charset="utf-8">
        <link rel="stylesheet" href="layout.css" type="text/css">
    </head>
    <body>
        <form action="register.php" method="post">
            <p>Name:</p>
            <input type="text" name="name">
            <p>Nachname:</p>
            <input type="text" name="nname">
            <p>Benutzername:</p>
            <input type="text" name="uname">
            <p>Telefonnummer:</p>
            <input type="tel" name="tel">
            <p>E-Mail:</p>
            <input type="email" name="email">
            <p>Passwort:</p>
            <input type="password" name="pass">
            <p>Passwort Wiederhohlen:</p>
            <input type="password">
            <br>
            <button type="submit">Account erstellen</button> 
            
        </form>
        
        
        
        
<?php
        
    
$db_host        = 'localhost';
$db_user        = 'root';
$db_pass        = '';
$db_database    = 'account_data'; 
/* End config */
$myConnection = mysqli_connect("$db_host","$db_user","$db_pass") or die ("could not connect to mysql"); 
mysqli_select_db($myConnection, "account_data") or die ("no database");          
        
        
$name = $_POST["name"];
$nname = $_POST["nname"];
$uname = $_POST["uname"];
$tel = $_POST["tel"];
$email = $_POST["email"];
$pass = $_POST["pass"];
        
echo $name;
echo $nname;
echo $uname;
echo $tel;
echo $email;
echo $pass;
        
if($name == "" or $nname ="" or $uname ="" or $tel ="" or $email ="" or $pass ="" ){
  echo "Du musst die mit * Makierten Felder ausfüllen!";
}else{
    
$eintrag = "INSERT INTO account_data
(Name, Nachname, Benutzername, Telefonnummer, Email, Passwort)
VALUES
('$name', '$nname', '$uname', '$tel', '$email', '$pass')";
    
$eintragen = mysqli_query($myConnection, $eintrag);
}
        
?>
        
    </body>
</html>[Edit Jörg; Codeblock eingefügt]