mysql-PHP,MySQL請問這兩行代碼有什麼區別？

mysqlphp

請問這兩行代碼有什麼區別？我試了一下都可以運行成功。

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

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

完整代碼from PHP和MySQL Web開發(原書第4版)：

             TODO supply a title                                
Book-O-Rama Book Entry Result
        ". "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', '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 was not added.";        }        $db->close();        ?>    

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