New Post: Aggregate Functions (SUM) using CAML

I'm trying to use aggregate functions in my CAML query specifically the SUM function.

I have a list that has a UserName column and an Amount column. I'm using SPServices to pull the list into a CEWP which I can do with no problem however I need to group the items by UserName and sum the Amount column for each user.

At the moment I'm stuck trying to SUM the Amount column. I simplified the sample below. I'm only pulling Amount column but cannot get it to sum. The CAML query is showing all items on the list without summing.

<script language="javascript" type="text/javascript">
$(document).ready(function() {
  $().SPServices({
    operation: "GetListItems",
    async: false,
    listName: "SampleList",
    CAMLViewFields: "<ViewFields><FieldRef Name='Amount' Type='SUM'/></ViewFields>",
    CAMLQuery: "<Query><Aggregations Value='Number'><FieldRef Name='Amount' Type='SUM'/></Aggregations></Query>",   
    completefunc: function (xData, Status) {
      $(xData.responseXML).SPFilterNode("z:row").each(function() {
        var varAmount = "<div>" + $(this).attr("ows_Amount") + "</div>";
        $("#calAmount").append(varAmount);
      });
    }
  });
});
</script>
<div>
<div id="calAmount" style="float:left; padding:5px;"></div>
</div>

Can someone help me out?