无法将JSON字符串从PHP文件传输到Jquery中的getJSON方法

This is what I want, on a PHP page called input.php the user submits a username by a html form. This gets stored into the MYSQL database. There is a page called results.php which querys the MYSQL database for all usernames.

What I need to happen is that every 5 or so seconds some jquery code (maybe getJSON) will get a JSON string from results.php (the same page). This JSON string may be updated as a user may of added more usernames on the input.php page.

This is the input.php file

        <form name="input" action="<?php $_SERVER['PHP_SELF']?>" method="post">
        Usernames: <input type="text" name="usernames" />
         <input type="submit" value="Submit" name="submit" />
    </form>

    <?php

    if(isset($_POST['submit'])) {
        $link = mysql_connect('', '', '');
        if (!$link) {
            die('Could not connect: ' . mysql_error());
        }

        $db_selected = mysql_select_db('', $link);
        if (!$db_selected) {
            die ('Can\'t use  : ' . mysql_error());
        }

        $result = mysql_query("INSERT INTO users(user_name)             VALUES('".$_POST['usernames']."')");
        if (!$result) {
            die('Invalid query: ' . mysql_error());
        }


    }
    ?>

This is the results.php file

    <script
        type="text/javascript" src="jquery-1.7.1.min.js"></script>
    <?php

    $link = mysql_connect('localhost', 'root', '');
    if (!$link) {
        die('Could not connect: ' . mysql_error());
    }

    $db_selected = mysql_select_db('test', $link);
    if (!$db_selected) {
        die ('Can\'t use test : ' . mysql_error());
    }

    $result = mysql_query("SELECT user_name FROM users");
    if (!$result) {
        die('Invalid query: ' . mysql_error());
    }


    $names = array();

    while ($row = mysql_fetch_assoc($result)) {

        foreach ($row as $key => $val) {

            $names[][$key] = $val;
        }
    }

    echo json_encode($names);


    ?>
    <script type="text/javascript"> 




        $.getJSON("http://localhost/test/results.php", function(json){
            alert("JSON Data: " + json);
        });

    </script>



    <div></div>

I am stuck on what jquery to put or even if i'm doing this properly. The end result is like Gmail where you receive email without a page refresh. But my system would retrieve usernames from the database every 5 seconds without a page refresh. I have read about getJSON method and I am totally out of my depth with it so I may need some very in depth explanation. If im going about this objective the wrong way please let me know and inform me of good practises in how to go about this.

I try this url in my browser with no result apart from the echoed JSON string from the php code.

this is my JSON string

[{"user_name":"matt"},{"user_name":"matt"},{"user_name":"peter"},{"user_name":"jim"},{"user_name":"sam"}]

If you want to use results.php to do both things (i.e. display the usernames as well as respond to the JSON query) then you will need to split the file into two branches. Use a _GET variable to specify which branch. So for example, you would run .getJSON on results.php?json=true instead of just results.php. Now inside results.php have an if branch that checks for the existence of this _GET variable, and if so, grab the data you need, echo it in a json-encoded string, and then exit(). Do all this before anything else in results.php, even before the <script> tag .

Edited to provide code: (edited from OP's question)

<?php
    $link = mysql_connect('localhost', 'root', '');
    if (!$link) {
        die('Could not connect: ' . mysql_error());
    }

    $db_selected = mysql_select_db('test', $link);
    if (!$db_selected) {
        die ('Can\'t use test : ' . mysql_error());
    }

    $result = mysql_query("SELECT user_name FROM users");
    if (!$result) {
        die('Invalid query: ' . mysql_error());
    }

    $names = array();

    while ($row = mysql_fetch_assoc($result)) {

        foreach ($row as $key => $val) {

            $names[][$key] = $val;
        }
    }

    if (isset($_GET['json'])) {
        echo json_encode($names);
        exit();
    }

    ?>
    <script type="text/javascript" src="jquery-1.7.1.min.js"></script>
    <script type="text/javascript"> 
        $.getJSON("http://localhost/test/results.php?json=true", function(json){
            alert("JSON Data: " + json);
        });
    </script>



    <div></div>

you can use setTimeout.

   setTimeout( function() {
    getData()
  }, 5000);

 function getData() {
    $.getJSON("http://localhost/test/results.php", function(json){
        alert("JSON Data: " + json);
    });
    });
   }

what you are looking for is called AJAX, you will need javascript in order to acomplish it. if you want a sleek and easy way I would recommend jQuery.Your code would look something like this:

setTimeout(function(){
    $.post("results.php",function(result){
        //Do somthing with the result Array or object
    },"json");
},5000);

moreover since you only are taking 1 piece of data "usernames" you should return an array json not an object json

["matt","matt","peter","jim","sam"]

it should take less bandwith for both, you and your user.

NOTE: you should remove the jquery script from results.php, the only thing you should retun is the json itself. if any doubt just ask