Greater Than by a set number

Question

Good afternoon, i've looked at a lot of things and can't seem to figure something out.

I am writing a program where a user inputs their vehicles mileage. Once that mileage is +3k, i want it to alert it's time for service, etc.

I am not sure how to accomplish this, if anyone can point me in a direction.

if reg_mileage = 35k, update_mileage = 38k, alert() is the idea.

Thank you!

if(isset($_POST['check_mileage'])) {
    
    $update_mileage = "UPDATE service_tracking SET update_mileage = '$reg_mileage' WHERE reg_vin = '$reg_vin'";
    $conn->exec($update_mileage);
    $check = $conn->query("SELECT reg_mileage, update_mileage FROM service_tracking WHERE (reg_mileage < update_mileage)");
    
    while($row = $check->fetch(PDO::FETCH_ASSOC)) {
        
        if($row > 38000) {
            echo "Time for an oil change";
        } else {
            echo "Up to date";
        }
    }
    
}

Answer 1

$row is an array, you can't compare it with a number. I think you want to subtract reg_mileage from update_mileage , and alert if the difference is less than 3K.

while ($row = $check->fetch(PDO::FETCH_ASSOC)) {
    if ($row['update_mileage'] - $row['check_mileage'] < 3000) {
        echo "Time for an oil change<br>";
    } else {
        echo "UP to date<br>";
    }
}

BTW, you probably should include the VIN or some other identifying information in the SELECT and output. Otherwise the user won't know which car needs the oil change.