Ajax请求和回调不起作用我尝试了多少

I have a simple PHP code that retrieves data from the table including image and stores it in a JSON object.

<?php
$con = mysql_connect("localhost","root","root");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
$selected = mysql_select_db("req2",$con)
or die("Could not select req2");
$table_first = 'locationtab';
$query=mysql_query("SELECT Id,City,Image FROM $table_first");

    while ($row=mysql_fetch_assoc($query)) {
        $array=$row;
        $array['Image']=base64_encode($row['Image']); 
       $output[]=$array;
    }

echo json_encode($output);

mysql_close($con);
?> 

This works perfectly fine and I'm able to view the JSON object using print. on the client side, I wrote a Javascript+Ajax code to call this PHP file and on success display the data in the JSON object. I dont know what is missing in the below code but I don't seem to get the AJAX part to work at all. PLease so help

<html>
<head>
<script src="file://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js">
</script>
<script>
$(document).ready(function(){ 
$.ajax({
     url:"table.php",
     dataType:'json',
     type:'POST',
      success:function(output) {
alert( output.Id );
               }
});

});
</script>
</head>
<body>
<p>test</p>
</body>
</html>

output is an array of objects with ids.

You are treating it as a single object with an id.

You need either a for loop, or to grab a specific index.

alert( output[0].Id );