PHP按钮返回404错误

<?php    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: $query<br />".mysql_error()."<br /><br />";    }        if(isset($_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<br />".mysql_error()."<br /><br />";            }        }        echo <<<_END        <form action="sqltext.php" method="post">                    <pre class="brush:php;toolbar:false;">                                  Author <input type="text" name="author" />                   Title <input type="text" name="title" />                Category <input type="text" name="category" />                    year <input type="text" name="year" />                    ISBN <input type="text" name="isbn" />                                        <input type="submit" value="ADD RECORD" />