ajax提交，后台老板没法写代码

$(document).ready(function(){  
        //post()方式  
        $('#test_post').click(function (){   
            $.post(  
                'ajax.php',  
                {  
                     		id:$("#id").val(),                   
                },  
                function (data) { //回调函数  
                    var myjson='';  
                    eval('myjson=' + data + ';');  
					alert(data);
                    $('#result').html("ID为:" + myjson.username);  
                }  
            );  
        });  
       
});  

  $a = $_POST["id"];	   
		 $conn  = mysql_connect("localhost","root",""); 
		 $my_db = mysql_select_db("demo",$conn);
		 $sql="select * from demo where id = $a";
	    $result = mysql_query($sql, $conn);
		$userInfo = mysql_fetch_assoc($result);             
	
	    print_r($userInfo);
	//   echo $a;