使用PHP将已定义的变量INSERT到MySQL DB /表中,没有数据(显然)被写入DB？

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$name = "John";
$age = 30;

$sql = "INSERT INTO users (name, age) VALUES ('$name', '$age')";

if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();