进行AJAX调用以更新数据库onChange of textarea

I am trying to create a feature on my website that automatically updates the database onchange of the textarea below (which is going to be act as a 'post-it note for reminders'). I am new to ajax, and I was wondering if someone can show me a basic example of how I would make an AJAX call to update my database onChange of the textarea below?

<?php
//Create mysql connect variable
$conn = mysql_connect('samplesource.com', 'example', 'pass');

//kill connection if error occurs
if(!$conn){
    die('Error: Unable to connect.' . '<br>' . mysql_error());
}
//connect to mysql database
mysql_select_db("mydb", $conn);

session_start();
$userid = $_SESSION['id'];

$results = ("SELECT * FROM notes WHERE userid='$userid'");
?>

<html>
<head>
<title>practice</title>
<script src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function() {     
    $(".sometext").change(function(){   
        //make ajax call to update database onChange    
    }); 
}); 
</script>
</head>
<body>

<textarea class="note" style="resize:none; width:300px; height:200px;"> </textarea>

</body>
</html>

First, you'd need to move your database save script into a new file e.g save.php

On your <textarea> i'd add

<textarea onchange="saveChanges(this);"></textarea>

For the javascript save function that's called when a change is made:

function saveChanges(object){   
    $.ajax({
        url: 'save.php',
        data: 'content=' + object.value,
        cache: false,
        error: function(e){
            alert(e);
        },
        success: function(response){
            // A response to say if it's updated or not
            alert(response);
        }
    });   
}

This is a very quick and dirty way of doing it.