使用PHP和MySQL不会将表单值添加到数据库表

Question

您好我使用bootstrap和PHP创建了一个rsvp表单。我是PHP和数据库连接的新手，所以我只想确认我正确地做了。我使用正确的语法，是否可以免受黑客攻击（SQL注入）等等。谢谢。

这是我的PHP：

<?php

        $servername = "rsvp.db";
        $username = "******";
        $password = "******";
        $dbname = "rsvp";

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

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

        function test_input($data) {
                $data = trim($data);
                $data = stripslashes($data);
                $data = htmlspecialchars($data);
                return $data;
        }

        if(isset($_POST["submit"])){

            $serverrsvp = test_input($_POST["formrsvp"]);
            $serverattend = test_input($_POST["formattend"]);
            $serverfullname = test_input($_POST["formfullname"]);
            $serveremail = test_input($_POST["formemail"]);
            $serverguests = test_input($_POST["formguests"]);
            $serverguestnames = test_input($_POST["formguestnames"]);
            $serverextras = test_input($_POST["formextras"]);

            $serverrsvp = mysqli_real_escape_string($conn, $serverrsvp);
            $serverattend = mysqli_real_escape_string($conn, $serverattend);
            $serverfullname = mysqli_real_escape_string($conn, $serverfullname);
            $serveremail = mysqli_real_escape_string($conn, $serveremail);
            $serverguests = mysqli_real_escape_string($conn, $serverguests);
            $serverguestnames = mysqli_real_escape_string($conn, $serverguestnames);
            $serverextras = mysqli_real_escape_string($conn, $serverextras);

            $sql = "INSERT INTO rsvp (dbrsvp, dbattend, dbfullname, dbemail, dbguests, dbguestnames, dbextras)
            VALUES ('$serverrsvp', '$serverattend', '$serverfullname', '$serveremail', '$serverguests', '$serverguestnames', '$serverextras')";

            if ($conn->query($sql) === TRUE) {
                echo "<script type= 'text/javascript'>alert('Thank you for your RSVP');</script>";
            } else {
                echo "<script type= 'text/javascript'>alert('Error: " . $sql . "<br>" . $conn->error."');</script>";
            }

            $conn->close();
        }
    ?>

这是我的HTML：

                <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
                    <div class="radio">
                        <label>Attending Wedding:<br>
                            <input  type="radio" name="formrsvp" value="Yes" aria-label="..." checked>Yes, because I'm awesome! <br>
                            <input  type="radio" name="formrsvp" value="No" aria-label="...">No, because I wish I was cooler... <br>
                        </label>
                    </div>
                    <div class="checkbox">
                        <label>Attending Friday Also?<br>
                            <input type="checkbox" value="Friday" name="formattend">Friday: Rehersal Dinner &amp; Beach Party <br>
                        </label>
                    </div>
                    <div class="form-group">
                        <label for="formfullname">Full Name:</label>
                        <input required type="name" name="formfullname" class="form-control" placeholder="Please enter your full name">
                    </div>
                    <div class="form-group">
                        <label for="formemail">Email Address:</label>
                        <input required type="email" name="formemail" class="form-control" placeholder="Please enter your email address">
                    </div>
                    <div class="select">
                        <label>Any Extra Guests:</label>
                        <select name="formguests" class="form-control">
                            <option value="0">0</option>
                            <option value="1">1</option>
                            <option value="2">2</option>
                            <option value="3">3</option>
                            <option value="4">4</option>
                            <option value="5">5</option>
                        </select>
                    </div>
                    <div class="textarea">
                        <label>Guest Names:</label>
                          <textarea name="formguestnames" class="form-control" rows="6" placeholder="Please enter the full name of any extra guests joining you..."></textarea>
                    </div>
                    <div class="textarea">
                        <label>Anything of Note:</label>
                          <textarea name="formextras" class="form-control" rows="10" placeholder="Please enter any specific information for the bride and groom, such as vegetarian guests, allergies, etc. If info is specific to a guest, please enter their name as well as info..."></textarea>
                    </div>
                    <br>
                    <button type="submit" value="Submit" name="submit" class="btn btn-default">Submit</button>
                </form>