สอบถามเรื่องการกรองข้อมูลค่ะ กรองข้อมูลแต่ละประเภทได้ แต่กรองข้อมูลทั้งหมดไม่ได้ค่ะ

if(!empty($_POST['id_ptype']) || $_POST['id_ptype']=='0'){
$sql = 'SELECT * FROM pawn , product , product_type'
. " WHERE pawn.id_pawn = product.id_pawn
AND product.id_ptype = product_type.id_ptype LIMIT 0, 30";

}else{
$sql = 'SELECT * FROM pawn , product , product_type'
. " WHERE pawn.id_pawn = product.id_pawn
AND product.id_ptype = product_type.id_ptype
AND product.id_ptype = ' ".$_POST['id_ptype']." ' LIMIT 0, 30"; 
}

<table width="859" border="0">
	<form action = "Goodr_repay.php" method="POST" >
		<tr>
			<td width="226">
				<div align="center">ประเภทสินค้า 
					<?php
						$dataproduct_type = mysql_query("SELECT * FROM `product_type`") OR die(mysql_error());
					?>
					<select name="id_ptype" >
						<option value="0">ทั้งหมด</option>;
					<?php while($fieldproduct_type = mysql_fetch_assoc($dataproduct_type)) : ?>
						<option value="<?php echo $fieldproduct_type['id_ptype']; ?>"><?php echo $fieldproduct_type['name_ptype']; ?></option>
					<?php endwhile; ?>
					</select>
					<input type="submit"value="ค้นหา">	
				</div>
			</td>
		</tr>
	</form>
</table>

<?php
$sql = 'SELECT * FROM `pawn` , `product` , `product_type`';
if(isset($_POST['id_ptype'])){
	//add where clause
	$sql = sprintf(
		"%s WHERE `pawn`.`id_pawn` = `product`.`id_pawn` AND `product`.`id_ptype` = `product_type`.`id_ptype` AND `product`.`id_ptype` = '%s' LIMIT 0, 30",
		$sql,
		(function_exists('mysql_real_escape_string')?mysql_real_escape_string($_POST['id_ptype']):mysql_escape_string($_POST['id_ptype']))
		); 
}

$data = mysql_query($sql) OR die(mysql_error());
$count = mysql_num_rows($data);
?>
<br /><br />
<table style="width: 716px; border: 1px solid #CCCCCC; background-color: #CCFF99">
	<thead>
		<tr style="background-color: #99FF33;">
			<th>เลขที่สัญญา</th>
			<th>ประเภทสินค้า</th>
			<th>ชื่อสินค้า</th>
			<th>รุ่น</th>
			<th>ราคาขายฝาก</th>
		</tr>
	</thead>
	<tbody>
		<?php while ($field=mysql_fetch_assoc($data)) : ?>
		<tr>
			<td><?php echo $fild['id_pawn']; ?></td>
			<td><?php echo $fild['name_ptype']; ?></td>
			<td><?php echo $fild['name_pro']; ?></td>
			<td><?php echo $fild['generation_pro']; ?></td>
			<td style="text-align: right;"><?php echo number_format($fild['price_pawn']); ?></td>
		</tr>
		<?php endwhile; ?>
	</tbody>
</table>
<br />