Calendar ดึงข้อมูลจากฐานข้อมูลมาโชว์ไม่ได้ครับ รบกวนด้วยครับ

<?php
header("Content-type:application/json; charset=UTF-8");          
header("Cache-Control: no-store, no-cache, must-revalidate");         
header("Cache-Control: post-check=0, pre-check=0", false);    
require("dbconnect.php");
if($_GET['gData']){  
    $q="SELECT * FROM tbl_event WHERE date(event_start)>='".$_GET['start']."'  ";  
    $q.=" AND date(event_end)<='".$_GET['end']."' ORDER by event_id";  
    $result = $mysqli->query($q);
    while($rs=$result->fetch_object()){
        $json_data[]=array(  
            "id"=>$rs->event_id,
            "title"=>$rs->event_title,
            "start"=>$rs->event_start,
            "end"=>$rs->event_end,
            "url"=>$rs->event_url,
            "allDay"=>($rs->event_allDay==true)?true:false      
            // กำหนด event object property อื่นๆ ที่ต้องการ
        );    
    }  
}
$json_data=(isset($json_data))?$json_data:NULL;
$json= json_encode($json_data);  
if(isset($_GET['gData']) && $_GET['gData']!=""){  
echo $_GET['callback']."(".$json.");";      
}else{  
echo $json;  
}

?>