Extend php register system

Question

I have the following table in mysql database :

CREATE TABLE IF NOT EXISTS `accounts` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `username` varchar(50) NOT NULL,
    `password` varchar(255) NOT NULL,
    `email` varchar(100) NOT NULL,
    PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

and a php system to handle the users . I want to add a new field to the register form like a selectable list : Beginner,Intermediate, Advanced, where user can select the status at the time they will fill the register form. How can I handle this new select list based on its values(Beginner,Intermediate, Advanced) in the mysql table and also in php code. Because based on experience I have a profile page that will displayed different information(also based on experience of the user). This is the original document : https://codeshack.io/secure-registration-system-php-mysql/

<form action="register.php" method="post" autocomplete="off">
                        <div class="form-group input-group">
                                <select class="form-control" name="invest">
                                    <option selected="">Investor Experience Level</option>
                                    <option>Beginner</option>
                                    <option>Intermediate</option>
                                    <option>Advanced</option>
                                </select>
                            </div> <!-- form-group end.// -->
                    <label for="username">
                        <i class="fas fa-user"></i>
                    </label>
                    <input type="text" name="username" placeholder="Username" id="username" required>
                    <label for="password">
                        <i class="fas fa-lock"></i>
                    </label>
                    <input type="password" name="password" placeholder="Password" id="password" required>
                    <label for="email">
                        <i class="fas fa-envelope"></i>
                    </label>
                    <input type="email" name="email" placeholder="Email" id="email" required>
                    <p>Already have an account? <a href="login.html">Login here</a>.</p>
                    <input type="submit" value="Register">
                </form>

<?php
// Change this to your connection info.
$DATABASE_HOST = 'localhost';
$DATABASE_USER = 'root';
$DATABASE_PASS = '';
$DATABASE_NAME = 'phplogindb';
// Try and connect using the info above.
$con = mysqli_connect($DATABASE_HOST, $DATABASE_USER, $DATABASE_PASS, $DATABASE_NAME);
if (mysqli_connect_errno()) {
    // If there is an error with the connection, stop the script and display the error.
    die ('Failed to connect to MySQL: ' . mysqli_connect_error());
}

// Now we check if the data was submitted, isset() function will check if the data exists.
if (!isset($_POST['username'], $_POST['password'], $_POST['email'])) {
    // Could not get the data that should have been sent.
    die ('Please complete the registration form!');
}
// Make sure the submitted registration values are not empty.
if (empty($_POST['username']) || empty($_POST['password']) || empty($_POST['email'])) {
    // One or more values are empty.
    die ('Please complete the registration form');
}

// We need to check if the account with that username exists.
if ($stmt = $con->prepare('SELECT id, password FROM accounts WHERE username = ?')) {

    if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
    die ('Email is not valid!');
    }

    if (preg_match('/[A-Za-z0-9]+/', $_POST['username']) == 0) {
    die ('Username is not valid!');
    }

    if (strlen($_POST['password']) > 20 || strlen($_POST['password']) < 5) {
    die ('Password must be between 5 and 20 characters long!');
    }

    // Bind parameters (s = string, i = int, b = blob, etc), hash the password using the PHP password_hash function.
    $stmt->bind_param('s', $_POST['username']);
    $stmt->execute();
    $stmt->store_result();
    // Store the result so we can check if the account exists in the database.
    if ($stmt->num_rows > 0) {
        // Username already exists
        echo 'Username exists, please choose another!';
    } else {
        // Username doesnt exists, insert new account
    if ($stmt = $con->prepare('INSERT INTO accounts (username, password, email) VALUES (?, ?, ?)')) {
        // We do not want to expose passwords in our database, so hash the password and use password_verify when a user logs in.
        $password = password_hash($_POST['password'], PASSWORD_DEFAULT);
        $stmt->bind_param('sss', $_POST['username'], $password, $_POST['email']);
        $stmt->execute();
        header('Location: login.html');
        echo 'You have successfully registered, you can now login!';
    } else {
        // Something is wrong with the sql statement, check to make sure accounts table exists with all 3 fields.
        echo 'Could not prepare statement!';
    }
    }
    $stmt->close();
} else {
    // Something is wrong with the sql statement, check to make sure accounts table exists with all 3 fields.
    echo 'Could not prepare statement!';
}
$con->close();
?>

Answer 1

First, add a column into your table to hold your value:

ALTER TABLE `mytable` ADD `myselect` TEXT NOT NULL; 

Next, make a select element in your form:

<form action = 'myphppage.php' method='post'>
    <select name='yourselect'>
        <option value='Advanced'>Advanced</option>
        <option value='Intermediate'>Intermediate</option>
        <option value='Beginner'>Intermediate</option>
    </select>
    <button type='submit'>Submit</button>
</form>

When the user clicks submit, the value of your select element will be sent in your $_POST array to 'myphppage.php', with the name of the element as an index.

<?php

   $select = $_POST['yourselect']; 

?>

Now that you have the value as a string, you can use the same methods you've posted above to insert the value into the database.

<?php

    if($stmt = $con->prepare('INSERT INTO `mytable`(`myselect`) VALUES (?)'){
        $stmt->bind_param('s', $select){
            $stmt->execute();
        }
    }

?>

Obviously, you'll need to tailor this to match the specifics of your situation, but this is the idea.

Answer 2

To add a new column to existing table you should run the following SQL command:

ALTER TABLE accounts ADD COLUMN experience ENUM('Beginner','Intermediate','Advanced') NULL DEFAULT 'Beginner' FIRST;

The advantage of enum column is that only the enumeration(1-3) is stored and not the strings.

Then the insert command will be

INSERT INTO accounts (username, password, email,experience ) VALUES (?, ?, ?, ?)

and the value for the experience column can be one of the strings 'Beginner','Intermediate','Advanced' or the corresponding numeric value 1,2,3