如何使用PHP实现微信小程序的在线测评功能？

<?php

$appid = 'YOUR_APPID';
$secret = 'YOUR_APP_SECRET';
$code = $_GET['code'];

$url = 'https://api.weixin.qq.com/sns/jscode2session?appid=' . $appid . '&secret=' . $secret . '&js_code=' . $code . '&grant_type=authorization_code';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
curl_close($ch);

$data = JSON_decode($result, true);

$openid = $data['openid'];
$session_key = $data['session_key'];

?>

<?php

$servername = 'YOUR_DB_SERVER';
$username = 'YOUR_DB_USERNAME';
$passWord = 'YOUR_DB_PASSWORD';
$dbname = 'YOUR_DB_NAME';

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = 'SELECT * FROM questions';
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    $questions = array();
    while ($row = $result->fetch_assoc()) {
        $questions[] = $row;
    }

    // 返回题目数据给小程序端
    echo json_encode($questions);
} else {
    echo 'No questions found.';
}

$conn->close();

?>

<?php

$servername = 'YOUR_DB_SERVER';
$username = 'YOUR_DB_USERNAME';
$password = 'YOUR_DB_PASSWORD';
$dbname = 'YOUR_DB_NAME';

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$openid = $_GET['openid'];
$answers = $_POST['answers'];

$sql = 'INSERT INTO answers (openid, answers) VALUES (' . $openid . ', ' . $answers . ')';
if ($conn->query($sql) === TRUE) {
    echo 'Answers saved successfully.';
} else {
    echo 'Error: ' . $sql . '<br>' . $conn->error;
}

$conn->close();

?>