รบกวนสอบถามหน่อยค่ะ คือส่งค่า ตัวแปรไม่ไปอ่ะคะ ไม่สามารถ where ออกมาได้

<!-- add ข้อมูลผู้ประสานงาน -->
    <script type="text/javascript">
            $(document).ready(function () {           
                var url = "data-con.php?id=<?=$id_school?>;"
                // prepare the data
                var source =
                {
                    datatype: "json",
                    datafields: [
						
                        { name: 'contact_name' }
						
                        
                    ],
                    id: 'con_id',
                    url: url,
                    async: false
                };
                var dataAdapter = new $.jqx.dataAdapter(source);
                // Create a jqxDropDownList
                $("#jqxWidget2").jqxDropDownList({ checkboxes: true, source: dataAdapter, displayMember: "contact_name", valueMember: "contact_name", width: 200, height: 25});
                $("#jqxWidget2").jqxDropDownList('checkIndex', 0);
                // subscribe to the checkChange event.
                $("#jqxWidget2").on('checkChange', function (event) {
                    if (event.args) {
                        var item = event.args.item;
                        if (item) {
                            var valueelement = $("<div></div>");
                            valueelement.text("Value: " + item.value);
                            var labelelement = $("<div></div>");
                            labelelement.text("Label: " + item.label);
                            var checkedelement = $("<div></div>");
                            checkedelement.text("Checked: " + item.checked);
                            $("#selectionlog").children().remove();
                            $("#selectionlog").append(labelelement);
                            $("#selectionlog").append(valueelement);
                            $("#selectionlog").append(checkedelement);
                            var items = $("#jqxWidget2").jqxDropDownList('getCheckedItems');
                            var checkedItems = "";
                            $.each(items, function (index) {
                                checkedItems += this.label + ", ";                          
                            });
                            $("#checkedItemsLog").text(checkedItems);
                        }
                    }
                });
            });
        </script>

<?php
#Include the connect.php file
include('connect.php');
//require_once('../Connections/myconnext.php'); 
 
#Connect to the database
//connection String
$id_school=$_GET['id'];

//$id_school=$_GET['id'];
//print_r('$_GET');
$connect = mysql_connect($hostname, $username, $password)
or die('Could not connect: ' . mysql_error());
//select database
mysql_select_db($database, $connect);
//Select The database
$bool = mysql_select_db($database, $connect);
if ($bool === False){
	print "can't find $database";
}
// get data and store in a json array
$query = "SELECT * FROM tte_contact WHERE cos_id_shool=".$_GET['id'];

echo $query;




$result = mysql_query($query) or die("SQL Error 1: " . mysql_error());
while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
	$customers[] = array(
		'con_id' => $row['con_id'],
        'contact_name' => $row['contact_name']
        
	
      );
	 

}

echo json_encode($customers);
?>