<?php
$error = "";
$con = mysqli_connect("localhost", "username", "password", "db_name");
if (!empty($_POST['signup'])) {
    $name = mysqli_real_escape_string($con, $_POST['name']);
    $email = mysqli_real_escape_string($con, $_POST['email']);
    $password = mysqli_real_escape_string($con, $_POST['password']);
    $birthday = mysqli_real_escape_string($con, $_POST['birthday']);
    $phone = mysqli_real_escape_string($con, $_POST['phone']);
    $country = mysqli_real_escape_string($con, $_POST['country']);
    $language = mysqli_real_escape_string($con, $_POST['language']);
    $user_check_query = "SELECT * FROM users WHERE email = '$email' LIMIT 1";
    $result = mysqli_query($con, $user_check_query);
    $user = mysqli_fetch_assoc($result);
    if ($user['email'] === $email) {
        $error .= "This email is already registered.";
    }
    else {
        $query = "INSERT INTO `users` (name, email, password, birthday, phone, country, language) VALUES ('$name', '$email', '$password', '$birthday', '$phone', '$country', '$language')";
        mysqli_query($con, $query);
        header("location: success.html");
    }
}
?>