Get value of two colums in jos_vm_product by sql on virtualmart

[pesidon]

i want get value in two colums product_weight,product_weight_uom  in jos_vm_product table,
i want display price in mod virtualmart similar :price /weight - weight unit 
ex : 50.000 / 3 kg
my code

<?php
$sql="SELECT product_weight,product_weight_uom FROM `jos_vm_product` WHERE product_id = '$product_id'";

$query=mysql_query($sql);


if(mysql_num_rows($query) == 0)

{

echo "Chua co du lieu";

}

else

{

while($row=mysql_fetch_array($query))

{


echo $row[product_weight] ." - ".$row[product_weight_uom]."<br />";

}

}
?>

now i want put if product_weight,product_weight_uom = 0 will echo "null"

<?php
$sql="SELECT product_weight,product_weight_uom FROM `jos_vm_product` WHERE product_id = '$product_id'";

$query=mysql_query($sql);


if(mysql_num_rows($query) == 0)

{

echo "Chua co du lieu";

}

else

{

while($row=mysql_fetch_array($query))

{
if ($row[product_weight]=0||$row[product_weight_uom]=0)
{
echo " null";
}
else {


echo $row[product_weight] ." - ".$row[product_weight_uom]."<br />";
}

}

}
?>

with some product not set value  product_weight,product_weight_uom in virtualmart
but  when i run it print "0"  instead "null"
any body help me
soory my english so bad !!
thanks for all!!

[pesidon]

thanks for alll , i fixed it and working wel 

if($row[product_weight]==0)

that correct