How To Insert Data Into MySql Using Php

<?php
    require_once("connection.php");

    if($_SERVER['REQUEST_METHOD'] == 'POST'){

        $fullName = test_input($_POST['fullname']);
        $Email = test_input($_POST['email']);
        $userName = test_input($_POST['username']);
        $passWord = test_input($_POST['password']);

        if(!empty($fullName) AND !empty($Email) AND !empty($userName) AND !empty($passWord)){

            if(filter_var($Email,FILTER_VALIDATE_EMAIL)){ // check if the email is valid or no

                if (preg_match('/^[0-9a-zA-Z ]+$/', $fullName)){ // the full name can contain only numbers ,letters and white space

                    $request = 'INSERT INTO users(fullname,email,username,password)
                    VALUES(:fullname,:email,:username,:password)';

                    $stmt = $connect->prepare($request);

                    $stmt->bindValue(':fullname',$fullName,PDO::PARAM_STR);
                    $stmt->bindValue(':email',$Email,PDO::PARAM_STR);
                    $stmt->bindValue(':username',$userName,PDO::PARAM_STR);
                    $stmt->bindValue(':password',$passWord,PDO::PARAM_STR);

                    $stmt->execute();

                    echo 'new record add to database';

                }else{

                    echo 'Unvalid Full Name ; Only Numbers ,Letters And White Space';
                     exit();
                }
            }else{

                echo 'Unvalid Email';
                exit();

            }
        }else{

            echo 'Unvalid Input';
             exit();
        }
    }

    function test_input($inputField){

        $inputField = htmlspecialchars(strip_tags(stripcslashes($inputField)));
        return $inputField;

    }
$connect = NULL;
?>

<!DOCTYPE html>
<html lang="en">
<head>
  <title>codeJs</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
</head>
<body>

<div class="container">
    <h2>Code Js : Register Now</h2>
        <form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']); ?>" method="POST">

            <div class="form-group">
                <label for="fullname">Full Name :</label>
                <input type="text" class="form-control" placeholder="Your Full Name" name="fullname">
            </div>

            <div class="form-group">
                <label for="email">Email :</label>
                <input type="text" class="form-control" placeholder="Your Email" name="email">
            </div>

            <div class="form-group">
                <label for="username">Username :</label>
                <input type="text" class="form-control" placeholder="Your Username" name="username">
            </div>

            <div class="form-group">
                <label for="password">Password:</label>
                <input type="text" class="form-control" placeholder="Your Password" name="password">
            </div>

            <button type="submit" class="btn btn-primary">Register</button>
            <a href='login.php' class="btn btn-warning">Log In</a>
        </form>
</div>


<style>form, h2{ width: 400px; margin: 0 auto; }
h2{ margin-top: 50px; margin-bottom: 30px; color: #ea4444; }
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
</body>
</html>