HI,小弟我是一个PHP新手，今天一个有关问题折腾了一下午，请大家帮小弟我看一上，万分感谢

HI,我是一个PHP新手，今天一个问题折腾了一上午，请大家帮我看一下，万分感谢

PHP code

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    <title>Book-O-Rama Book Entry Results</title>
    <style type="text/css">
    
    </style>
    <script type="text/javascript"></script>
    <script>
    
    </script>


    <h1 id="Book-O-Rama-Book-Entry-Result">Book-O-Rama Book Entry Result</h1>
    <?php //create short variable names
        $isbn = $_POST['isbn'];
        $author = $_POST['author'];
        $title = $_POST['title'];
        $price = $_POST['price'];
        
        if ( !$isbn || !$author || !$title || !$price ) {
            echo "You have not entered all the required details.<br/>"."Please go back and try again.";
            exit;
        }
        if ( !get_magic_quotes_gpc() ) {
            $isbn = addslashes($isbn);
            $author = addslashes($author);
            $title = addslashes($title);
            $price = doubleval($price);
        }
        
        @ $db = new mysqli('localhost', 'bookorama', 'bookorama123', 'books');
        if ( mysqli_connect_errno() ) {
            echo "Error: Could not connect to database. Please try again later.";
            exit;
        }
        
        $query = "insert into books values ('$isbn', '$author', '$title', '$price')or die(mysql_error())";
;
        
        echo $query;
        
        $result = $db->query($query);
        
        if ( $result ) {
            echo mysqli_affected_rows." book inserted into database.";
        } else {
            echo mysql_errno()."".mysql_error();
            echo "An error has occurred.The item was not added.";
        }
        
        $db->close();
        
    ?>

这是来自PHP和 MySQL web开发（第四版）中的一段代码。
我想问的是为什么最后总是输出An error has occurred.The item was not added
而且插入结果$result = -1 
请大家指点一下

------解决方案--------------------
$query = "insert into books values ('$isbn', '$author', '$title', '$price')";


echo $query;

$result = $db->query($query) or die($db->error);