Mysql-php,mysql What is the difference between these two lines of code?

mysqlphp

What is the difference between these two lines of code? I tried it all to run successfully.

 $query = "insert into books values (' ".$isbn." ', ' ".$author." ', ' ".$title." ', ' ".$price." ')";

Full code from PHP and MySQL Web development (Original book 4th edition):

             <title>TODO supply a title</title>        
   
    
           
   
    
                   
Book-o-rama Book Entry Result
        
   ". "            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 ', ' root ', ' 123 ', ' mydb '); 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."        ')";        $result = $db->query ($query); if ($result) {echo $db->affected_rows.        "Book inserted into Database"; } else {echo "An error has occurred.        The item is not added. ";}        $db->close (); ?>

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