Radi

<?php

define('HOST', 'localhost');
define('USER', 'root');
define('PASS', '');
define('NAME', 'radi');
define('TABLE', 'books');

$result = null;

try {
    $conn = new PDO('mysql:host='. HOST .';dbname='. NAME, USER, PASS);

    // errmode enabled
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

} catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

if(isset($_POST['update'])) {
    $title = htmlentities($_POST['title'], ENT_QUOTES, 'UTF-8');
    $author = htmlentities($_POST['author'], ENT_QUOTES, 'UTF-8');

    $sql = 'UPDATE ' . TABLE . ' SET ' . (!empty($title) ? 'title = \'' . $title . '\'': '') . ' ' . (!empty($author) ? ', author = \'' . $author . '\'' : '') . ' WHERE id = ' . htmlentities($_GET['book'], ENT_QUOTES, 'UTF-8');

    $stmt = $conn->prepare($sql);
    $stmt->execute();

    echo 'Successfully updated ' . $stmt->rowCount() .' rows!';

} else if(isset($_GET['book'])) {
    $sql = 'SELECT * FROM books WHERE id = ' . htmlentities($_GET['book'], ENT_QUOTES, 'UTF-8');

    $stmt = $conn->prepare($sql);
    $stmt->execute();

    $result = $stmt->fetchAll(PDO::FETCH_OBJ);
}

?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <form method="post">
        <label for="title">Title:</label><br>
        <input type="text" name="title" id="title" value="<?= isset($result) ? $result[0]->title : "" ?>">

        <br><br>

        <label for="author">Author:</label><br>
        <input type="text" name="author" id="author" value="<?= isset($result) ? $result[0]->author : "" ?>">

        <br><br>

        <button type="submit" name="update">Update Data</button>
    </form>
</body>
</html>