Using variable as value in post to php/mysql - php

Question

I get a random row from a mysql-server using php. I then display some information and would like to let the users give feedback on that specific row. However, I can't seem to transfer the ID correctly to the update.php. (No updating is happening on the server). Can somebody spot out my error?
Mysql-php getting a (ugly) random row:
$con = mysql_connect($host,$user,$pass);
$dbs = mysql_select_db($databaseName, $con);
mysql_query("SET CHARACTER SET utf8");
mysql_query("SET NAMES utf8");
$result = mysql_query("SELECT id, username, message, ttime, field1, field2 FROM field WHERE done = 0 ORDER BY RAND() LIMIT 1");
$array = mysql_fetch_row($result);
echo json_encode($array);
Then index.php:
<div id="output">
<div id="username">content</div>
<script id="source" language="javascript" type="text/javascript">
$(function ()
{ $.ajax({
url: 'api.php',
data: "",
dataType: 'json',
success: function(data)
{
var id = data[0];
var vname = data[1];
var message = data[2];
var timestamp = data[3];
$('#output').html(timestamp +message );
$('#username').html( vname );
}
});
});
</script>
<script>
$(document).jkey('a',function() {
$.post("update.php", { id: "id"} )
});
</script>
Then in the update.php:
<?php require_once('Connections/connection.php'); ?>
<?php
$id = $_POST['id'];
$sql = "UPDATE field SET field1 = field1 +1 WHERE id = '$id'";
$result = mysql_query($sql);
?>

Answer 1

Put a global _id in a script tag, then :
$.ajax({
url: 'api.php',
data: "",
dataType: 'json',
success: function(data)
{
var id = data[0];
_id = id;
//...
and
<script>
$(document).jkey('a',function() {
$.post("update.php", { "id": _id} ) // <--- Look here
});
</script>

Answer 2

$.post("update.php", { id: "id"} )
is sending the Stringid to the server as the id. You'll want to replace it with the actual variable that holds the id number based on which row the user selected, for example
$.post("update.php", { id: rowIDNum} )
If you provide some information on how the user is selecting a row, I can provide more details on how to determine the value to put in rowIDNum.