index.html
<script src="http://code.jquery.com/jquery-latest.min.js" type='text/javascript'></script>
<script>
$(document).ready(function(){
$("#insert").click(function(event){
$.post('insert.php',{username:$(this).html()});
})
});
</script>
<a href='javascript:void(0);' id='insert'>Username</a>
insert.php
<?php
function insert($username){
$conn = mysql_connect("host","user","passwd");
if($conn){
$username = mysql_real_escape_string($_POST['username']);
$result = mysql_query("INSERT INTO test.user(username) VALUES('".$username."')") or die(mysql_error());
mysql_close($conn);
}
}
if(isset($_POST['username'])){
insert($_POST['username']);
}
?>