如何使表单在其值在php中的数据库中后消失

$servername = "数据库服务器名称";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名称";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

$sql = "CREATE TABLE users (
    id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(30) NOT NULL,
    password VARCHAR(30) NOT NULL
)";

if ($conn->query($sql) === TRUE) {
    echo "表创建成功";
} else {
    echo "创建表时出错: " . $conn->error;
}

$username = $_POST['username'];
$password = $_POST['password'];

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

if ($conn->query($sql) === TRUE) {
    echo "数据插入成功";
} else {
    echo "插入数据时出错: " . $conn->error;
}

$username = $_POST['username'];

$sql = "DELETE FROM users WHERE username = '$username'";

if ($conn->query($sql) === TRUE) {
    echo "数据删除成功";
} else {
    echo "删除数据时出错: " . $conn->error;
}