PHP PDO How do I correctly remove record using DELETE FROM?

Every 15 minutes we update our stock quantity.  Is this the proper way to delete a product if the product becomes out of stock?  Please note: There is a master download that updates all products every morning.

$conn->query("DELETE FROM `oc_product` WHERE quantity == 0");

$filename="http://datadownloads.**********.net/data/count.csv";



//rebs,rebe,spec,os&time= . $time . ";
//open the file
$handle = fopen($filename, "r");
//this is what causes it to skip
fgetcsv($handle,",");



//begin looping through the lines
while (($data = fgetcsv($handle, ",")) !== FALSE)
{


// loop all column values and escape special characters
 foreach ($data as $key => $value){
  $data[$key] = $value;
}

//Update stock
$conn->query("UPDATE `oc_product` SET quantity = $data[3] WHERE product_id = $data[0]");

//echo $data[0]."&nbsp;&nbsp;".$data[3]."<BR>";

//Delete Out Of Stock Items from Database
$conn->query("DELETE FROM `oc_product` WHERE quantity == 0");

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