php insert语句不起作用，代码被忽略[重复]

I'm working on a simple register page to learn php but i have 2 big problems

  1. When I press register i get this error: Error:INSERT INTO users (username, password) VALUES (hello12345, hello12345) Unknown column 'hello12345' in 'field list'

  2. My if statements which checks the username/password length, and the ones which check if password and confirm password match are beeing ignored

My database table looks like this:

CREATE TABLE users (
  id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL UNIQUE, 
  password VARCHAR(255) NOT NULL,
);

and the php is

include("config.php");


$username = "";

$password = "";

$passwordConfirm = "";

$usernameError = "";

$passwordError ="";

$passwordConfirmError ="";



if($_SERVER["REQUEST_METHOD"] == "POST"){



if(empty(trim($_POST["username"]))) {
    $usernameError =  "Bitte geben Sie einen Benutzernamen ein";
}else {
    $username = trim($_POST["username"]);
}




}



if(empty(trim($_POST["password"]))) {

    $passwordError = "Bitte geben Sie ein Passwort ein";

} elseif (strlen(trim($_POST["password"])) < 6) {

    $passwordError = "Password muss mindestens 6 Zeichen lang sein";

} else {

    $password = trim($_POST["password"]);

}



if(empty(trim($_POST["passwordConfirm"]))) {

    $passwordError = "Bitte bestätigen Sie ihr Passwort.";

} else {

    $passwordConfirm = trim($_POST["passwordConfirm"]);

    if($password != $passwordConfirm) {

        $passwordConfirmError = "Passwörter stimmen nicht überein";

    }

}



if(empty($usernameError) && empty($passwordError) && empty($passwordConfirmError)) {



$sqlStatement = "INSERT INTO users (username, password) 
                 VALUES ($username, $password)";



if(mysqli_query($connection, $sqlStatement)) {
    echo "Registrierung erfolgreich";
} else {
    echo "Error:" .$sqlStatement . "&lt;br&gt;" . mysqli_error($connection);
}




}



?>



<!DOCTYPE html>

<html>

<head>

    <meta charset="UTF-8">

    <title>Registrieren </title>

</head>

<body>



<div>

    <h2>Registrieren</h2>

    <p>Bitte erstelle eine Account</p>

    <form action="register.php" method="post">

        <input type="text" name="username" placeholder="Benutzername">

        <input type="text" name="password" placeholder="Passwort">

        <input type="text" name="passwordConfirm" placeholder="Passwort bestätigen">

        <br>

        <button type="submit" name="submit" value="submit">Registrieren</button>

        <br>

    </form>

</div>

</body>

</html>