PHP incrementing a var - php

Question

I am building a car parking application in which different users have different numbers of parking spots. This number is set by an administrator in a database. The user can input a numberplate which then will be added to a database as well. What I want is that when a user has occupied all the spots, that he will not be able to insert any more number plates.
However, now I have the following code at the moment:
if(isset($_POST['number_plate'])){
$numberPlate = $_POST['number_plate'];
$user_id = $_SESSION['id'];
$query = mysql_query("SELECT `parking_spots` FROM `login` WHERE `id` = ".$user_id." ");
$row = mysql_fetch_assoc($query);
$totalNumberOfSpots = $row['parking_spots'];
$occupiedNumberOfSpots = 0;
$sql = "INSERT INTO amsterdam (numberplate, user_id) VALUES ('$numberPlate','$user_id')";
if(mysql_query($sql))
{
echo 'numberplate added';
$occupiedNumberOfSpots++;
if($occupiedNumberOfSpots == $totalNumberOfSpots)
{
echo "There are no more spots avialable";
}
}
else
{
echo 'Something went wrong!';
}
}
But when I echo the $occupiedNumberOfSpots variable it keeps returning 1 and does not increment every time I add numberplate.
How can I solve this issue?

Answer 1

It is because You are running the same code each time You add a plate to your db.
this:
$occupiedNumberOfSpots = 0;
should be taken from db as well. I guess it should be like that:
$totalNumberOfSpots = 100; // for example
$occupiedNumberOfSpots = $row['parking_spots']; // taken from db
instead of:
$totalNumberOfSpots = $row['parking_spots'];
$occupiedNumberOfSpots = 0;