试图更新表中的图像，但未执行更新

i am trying to updata image in register table by default i allowed null there.

当用户登录时，他/她可以上传他们的照片，这会导致注册表更新，但只有更新不执行，这里是我的php代码和数据到php页面来自Asynktask类。更新后，我发送json响应到android应用程序。注册表包含名为user_image的图像字段

   $email=$_POST['email'];
   $name = $_POST['name'];
    $phone= $_POST['mobile'];
    $userimage = mysql_real_escape_string($_POST['image']);
    // include db connect class
    require_once __DIR__ . '/db_connect.php';
    $db = new DB_CONNECT();
    $q="UPDATE  register SET  name ='$name',
        user_image ='$userimage',
        phone_number = '$phone' WHERE  register.email ='$email'";// check if row inserted or not
    if ($result) {
        // successfully inserted into database
        $response["success"] = 1;
        $response["message"] = "User Info successfully Updated.";
        // echoing JSON response
        echo json_encode($response);
    } else {
        // failed to insert row
        $response["success"] = 0;
        $response["message"] = "Oops! An error occurred.";
        // echoing JSON response
        echo json_encode($response);
    }
?>

这里是我的Asynkask类，我从图像发送数据到上面提到的php页面类UpdateInfo扩展AsyncTask {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(Myinfo.this);
        pDialog.setMessage("Updating Please Wait..");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }
    protected String doInBackground(String... args) {
                    List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("email", email_id));
        params.add(new BasicNameValuePair("name", uname));
        params.add(new BasicNameValuePair("mobile", umobile));
        params.add(new BasicNameValuePair("image",setImageString));
        JSONObject json = jsonParser.makeHttpRequest(url_update_info,
                "POST", params);
        // check log cat fro response
        Log.d("Create Response", json.toString());
        // check for success tag
        try {
            int success = json.getInt(TAG_SUCCESS);

        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog once done
        pDialog.dismiss();
    }
}