ขอสอบถามการเช็คค่าซ้ำก่อนบันทึกข้อมูล ของ PHP sqlsrv ครับ

	$sql = "INSERT INTO RFID_Master (
	EmpID, RFIDNo, Status, 
	CreatedBy, CreatedDate) VALUES (?, ?, ?, ?, ? )";
	$params = array($_POST["txtempID"], $_POST["txtRFID"], "1", $_POST["txtCreator"], $_POST["txtCdate"]);

	$stmt = sqlsrv_query( $conn, $sql, $params);
	if( $stmt === false ) {

		echo "<script type=text/javascript>alert('Unsuccessful error!');javascript:history.back(1);</script>";
		exit();

	}
	else
	{
		echo "<script type=text/javascript>alert('Successfully Record');javascript:history.back(1);</script>";
		exit();
	}