รบกวนสอบถามครับคือผมอยากจะเช็คจำนวนก่อนส่งข้อมูลคับถ้าน้อยกว่าให้ส่งค่าเป็น 0

<?php 
$checkZ = "SELECT * FROM paper ";
$checkZZ = mysqli_query($conn,$checkZ);
$rowZ = mysqli_fetch_array($checkZZ,MYSQLI_ASSOC);
$z = 0;
$p = $rowZ["p_price"];
$t1 = 1;
$t2 = $rowZ["p_qty"];
if($t2 < $t1){
   echo $z;
}else{
   echo $p;
}
?>

<?php
$conn = new mysqli("localhost","root","12345678", "mydatabase") or die( mysqli_connect_error());
$conn = "SET CHARACTER SET UTF8";
$strSQL = "SELECT * FROM paper WHERE 1 AND p_id = '".$_POST["p_id"]."' ";
$result = $conn->query($strSQL) or die ($conn->error);
//$intNumField = $result->field_count(); 
$resultArray = array();
while($row = $result->fetch_assoc()){ 
	$resultArray[]=$row;
	}
$conn->close();
echo json_encode($resultArray);
?>

//หน้าแสดงผลคับ
<script type="text/javascript">
$(document).ready(function(){

	$("#p_id").change(function(){
		$.ajax({ 
				url: "rpdcheck.php" ,
				type: "POST",
				data: 'p_id=' +$("#p_id").val()
			})
			.success(function(result) { 

				var obj = jQuery.parseJSON(result);
				
					if(obj == '')
					{
						alert('ไม่พบข้อมูล !!  หรือคุณยังไม่ได้เพิ่มข้อมูล !!'); 
						//window.location='index.php';
						return false;
					}
					else
					{
						  $.each(obj, function(key, inval) {

							   $("#p_id").val(inval["p_id"]);
							   $("#p_name").val(inval["p_name"]);
							   $("#p_price").val(inval["p_price"]);
							   $("#p_picture").val(inval["p_picture"]);
							   $("#p_qty").val(inval["p_qty"]);
						  });
					}

			});

		});
	});
</script>