Untitled

<?php
$servername = "localhost";
$username = "root";
$password = "";
$database = "palabasan_db";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $database);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
?>

<html>
<head>
<script type="text/javascript" src="jquery.js"></script>
        <script>
            $(document).ready( function() {
                $("#target").submit( function(event)

                    var errorMessage = "";
                    if($(".requiredUsername").val() == "")
                    {
                        errorMessage = errorMessage + "Please fill in the username\n";
                        //This code is used so that the page won't be submitted if there are errors.
                        event.preventDefault();
                    }
                    if($(".requiredPassword").val() == "")
                    {
                        errorMessage = errorMessage + "Please fill in the password\n";
                        //This code is used so that the page won't be submitted if there are errors.
                        event.preventDefault();
                    }

                    if($(".requiredFirstName").val() == "")
                    {
                        errorMessage = errorMessage + "Please fill in the firstname\n";
                        //This code is used so that the page won't be submitted if there are errors.
                        event.preventDefault();
                    }

                    if($(".requiredLastName").val() == "")
                    {
                        errorMessage = errorMessage + "Please fill in the lastname\n";
                        //This code is used so that the page won't be submitted if there are errors.
                        event.preventDefault();
                    }

                    //This code checks wheter the errorMessage variable contains error messages
                    if (errorMessage != "")
                    {
                        alert(errorMessage);
                    }
                });
            });
        </script></head>
        <body>

        <?php
    $username = "";
    $password = "";
    $firstname = "";
    $middlename = "";
    $lastname = "";


    if(isset($_POST['username']))
    {
        $username = $_POST['username'];
        $password = $_POST['password'];
        $firstname = $_POST['firstname'];
        $middlename = $_POST['middlename'];
        $lastname = $_POST['lastname'];

     $sql = 'SELECT username FROM tbl_joshua';
        $result = mysqli_query($conn,$sql);
        if(mysqli_num_rows($result) > 0 )
        {
        while($row = mysqli_fetch_assoc($result))
        {
            if($username == $row["username"])
            {
            echo "Username exist";
            exit;
            }
            }
            }


        if (preg_match('/^[a-z\d_]{2,20}$/i', $username)) {
        $sql = 'INSERT INTO tbl_joshua(username, password,firstname,middlename,lastname) VALUES("'.$username.'","'.$password.'","'.$firstname.'","'.$middlename.'","'.$lastname.'")';

        if ($conn->query ($sql) === TRUE){
        echo "Successfully Added";
        } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
        }
        echo "";
        }
        else
        {
        echo "Invalid!(No special characters)";
        }
    }


?>
        <form id="target" method="post" action="midterms.php">
            Username: <input pattern=".{6,20}" class="requiredUsername" type="text" name="username"   <?php echo $username; ?> > <br/>
            Password: <input  pattern=".{8,100}" class="requiredPassword" type="text" name="password"   <?php echo $password; ?> > <br/>
            Firstname: <input  type="text" class="requiredFirstName" type="text" name="firstname"  <?php echo $firstname; ?>> <br/>
            Middlename: <input type="text"  type="text" name="middlename"   <?php echo $middlename; ?> > <br/>
            Lastname: <input  type="text" class="requiredLastname" type="text" name="lastname"  <?php echo $lastname; ?>> <br/>


            <input type="submit" />
        </form>
    </body>
</html>