PHP按钮返回404异常

    require_once 'login.php';
    $db_server = mysql_connect($db_hostname,$db_username,$db_password);

    if(!$db_server)die("Unable to connect to MySQL:".mysql_error());

    mysql_select_db($db_database)
    or die("Unable to select to MySQL:".mysql_error());
    
    if(isset($_post['delete']) && isset($_POST['isbn']))
    {
        $isbn = get_post('isbn');
        $query = "DELETE FROM classics WHERE isbn='$isbn'";
        
        if(!mysql_query($query, $db_server))
        echo "DELETE failed: $query
".mysql_error()."

";
    }
    
    if(isset($_post['author']) &&
       isset($_post['title']) &&
       isset($_post['category']) &&
       isset($_post['year']) &&
       isset($_post['isbn']))
        {
            $author = get_post('author');
            $title = get_post('title');
            $category = get_post('category');
            $year = get_post('year');
            $isbn = get_post('isbn');
            
              $query = "INSERT INTO classics VALUES".
              "('$author','$title','$category','$year','$isbn')";  
              
            if(!mysql_query($query, $db_server))
            {
                echo "INSERT failed: $query
".mysql_error()."

";
            }
        }
    
    echo <<<_END

        
        
_END;
    
    $query = "SELECT * FROM classics";
    $result = mysql_query($query);
    
    if(!$result) die("Datebase access failed: ".mysql_error);
    
    $rows = mysql_num_rows($result);
    
    for($j = 0; $j<$rows; ++$j)
    {
        $row = mysql_fetch_row($result);
            echo <<<_END
        

               Author $row[0]
                Title $row[1]
             category $row[2]
                 year $row[3]
                 ISBN $row[4]
        

        
            
_END;
    }
    
    mysql_close($db_server);
    
    function get_post($var)
    {
            return mysql_real_escape_string($_POST[$var]);
    }

?>