loop statement breaking - php

Question

please why is the loop statement breaking, after the multiplication it only update the last row, tried using a foreach loop for the $totalprice in the update statement it says invalid argument.
if(array_key_exists('item', $_POST)){
// $items = $_POST['item'];
//foreach($_POST['item'] as $item){
//echo $item['Pquantity'] . ", ";
//echo $item['Pidno'] . ", ";
// }
//Loop through $_POST items, updating the database for each item
foreach ($_POST['item'] as $item) {
$Pquantity = intval($item['Pquantity']);
$Pidno = ($item['Pidno']);
//echo $Pquantity . ", ";
//echo $Pidno . ", ";
//$totalprice = intval($item['Pquantity'])
$queryreg = mysql_query("
UPDATE repplac
SET Pquantity = {$Pquantity}
WHERE
Pidno = '{$Pidno}'
AND
Uname = '{$_SESSION['username']}'
") or die(mysql_error());
}
}
$pplresult = mysql_query("SELECT * FROM repplac WHERE Uname = '{$_SESSION['username']}'") or die(mysql_error());
while ($row = mysql_fetch_assoc($pplresult))
{
$totalprice = $row['Price'] * $row['Pquantity'];
//echo "$totalprice";
//die();
$queryreg = mysql_query("
UPDATE repplac
SET Tprice = {$totalprice}
WHERE
Pidno = '{$Pidno}'
AND
Uname = '{$_SESSION['username']}'
") or die(mysql_error());
}

Answer 1

Neither arguments in the second condition gets changed inside the loop:
WHERE
Pidno = '{$Pidno}'
AND
Uname = '{$_SESSION['username']}
Perhaps you forgot to update $Pidno?
Also, I don't think the following is safe:
"SELECT * FROM repplac WHERE Uname = '{$_SESSION['username']}'"
You might want to sanitize $_SESSION['username'] before passing it to the query.

Answer 2

Inside your foreach you update $Pidno with the following code
$Pidno = ($item['Pidno']);
Thus you are updating different records in the database. But inside your while loop $Pidno is staying the same the entire time. Thus you are updating the same record over and over. To fix this add the following code at the beginning of the while loop
while ($row = mysql_fetch_assoc($pplresult))
{
//get the correct Pidno for this row
$Pidno = ($row['Pidno']);
$totalprice = $row['Price'] * $row['Pquantity'];
// ... the rest of your while loop