รบกวนผู้รู้ สอบถามการ DateDiff กับวันที่ปัจจบัน SQL

select  datediff('2558-10-01',concat(date_format(now(),'%Y')+543,'-',date_format(now(),'%m-%d')))*-1;

select 
  datediff( 
    concat( left(dte, 4)-543, right(dte, 6) ), 
    now() 
  )

<?php
	
	if($cal_date==1)
	{
	//mail	
$user_mail=$_POST['user_mail'];
$user_id=$_POST['user_id'];
$user_name=$_POST['user_name'];
$user_lastname=$_POST['user_lastname'];
$type_name=$_POST['type_name'];
$borrow_id=$_POST['borrow_id'];
$date_borrow=$_POST['date_borrow'];
$cal_date=$_POST['cal_date'];
error_reporting(0);
	require_once('PHPMailer_v5.0.2/class.phpmailer.php');
	$mail = new PHPMailer();
	 $mail->CharSet = "utf-8"; 
	$mail->IsHTML(true);
	$mail->IsSMTP();
	$mail->SMTPAuth = true; // enable SMTP authentication
	$mail->SMTPSecure = "ssl"; // sets the prefix to the servier
	$mail->Host = "smtp.gmail.com"; // sets GMAIL as the SMTP server
	$mail->Port = 465; // set the SMTP port for the GMAIL server
	$mail->Username = "[email protected]"; // GMAIL username
	$mail->Password = "123456789"; // GMAIL password
	$mail->From = "admin"; // "[email protected]";
	//$mail->AddReplyTo = "[email protected]"; // Reply
	$mail->FromName = "Center ";  // set from Name
	$mail->Subject = "แจ้งเตือนจากระบบ"; 
	$mail->Body = "
	<b>
	เรียนคุณ $user_name  $user_lastname </b></br> 
	
	
การยืมอุปกรณ์คอมพิวเตอร์ของคุณได้ครบกำหนดวันคืนแล้วค่ะ</br>
	";
	
	
	$mail->AddAddress($user_mail,$user_name); // to Address

	$mail->set('X-Priority', '1'); //Priority 1 = High, 3 = Normal, 5 = low

	$mail->Send(); 
	
	
	}
	?>