PHP - Subtract Datetime To Get Total Hours And Days

$days = array("sun","mon","tue","wed","thu","fri","sat");
$today = date("w");
$yesterday = $days[$today - 1];

# ./update.php 
PHP Notice:  Undefined offset: -1 in /root/fcc/work/update.php on line 6
fetching l_am_.zip
ncftpget: server said: l_am_.zip: No such file or directory.
PHP Warning:  unlink(counts): No such file or directory in /root/fcc/work/update.php on line 23
data set empty nothing to process 

Sun, 01 February, 2015 6:29:06 PM

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////
Maximumize / calling the quantity from Database
/////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
if(isset($_GET['add'])){
$quantity = mysqli_query($db_conx,'SELECT id, quantity FROM products WHERE id='.mysqli_real_escape_string($db_conx,(int)$_GET['add']));
while ($row = mysqli_fetch_assoc($quantity)){
if ($row['quantity']!=$_SESSION['cart_'.(int)$_GET['add']]) {
$_SESSION['cart_'.(int)$_GET['add']]+='1';
}
}
header('Location: '.$page);
}

if(isset($_GET['remove'])){
$_SESSION['cart_'.(int)$_GET['remove']]--;
header('Location:' .$page); 
}

if(isset($_GET['delete'])){
$_SESSION['cart_'.(int)$_GET['delete']]='0';
header('Location:' .$page); 
}

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////
Calling all products from Database
/////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
function products($db_conx){
$get = mysqli_query($db_conx,"SELECT id, name, description, price FROM products WHERE quantity > 0 ORDER BY id DESC"); 
if (mysqli_num_rows($get) ==0){
echo "There are no products to display";
}
else {
while ($row = mysqli_fetch_assoc ($get)){
echo '<p>'.$row ['name']. 
'<br/>
<br/>'
.$row ['description']. 
'<br/>
<br/>'
.'&dollar;'.number_format($row['price'], 2).' <a href="cart.php?add='.$row ['id'].'">Add</a></p>';
}
}
}

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////
Paypal Checkout
/////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
function paypal_items($db_conx){
$num = 0;
foreach($_SESSION as $name => $value){
if ($value != 0){
if(substr($name, 0, 5)=='cart_'){
$id = substr($name, 5, strlen($name) -5);
$row = mysqli_query($db_conx,'SELECT id, name, price, shipping FROM products WHERE id ='.mysqli_real_escape_string($db_conx,(int)$id));
while ($query = mysqli_fetch_assoc($row)){
$num++;
echo '<input type="hidden" name="item_number_'.$num.'" value="'.$id.'">';
echo '<input type="hidden" name="item_name_'.$num.'" value=" '.$query['name'].' ">';
echo '<input type="hidden" name="amount_'.$num.'" value=" '.$query['price'].' ">';
echo '<input type="hidden" name="shipping_'.$num.'" value=" '.$query['shipping'].' ">';
echo '<input type="hidden" name="quantity_'.$num.'" value=" '.$value.' ">';
}
}
}
}
}


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////
Shopping Cart View
/////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
function cart($db_conx) {
foreach($_SESSION as $name => $value) {
if ($value > 0) {
if(substr($name,0 ,5) . 'cart_'){
$id = substr($name, 5, (strlen($name) -5));
$row = mysqli_query($db_conx,'SELECT id, name, price FROM products WHERE id=' .mysqli_real_escape_string ($db_conx,(int)$id));
while ($query = mysqli_fetch_assoc($row)){
$sub = $query['price']*$value;
echo $query['name'].' x ' .$value. ' @ &dollar;' .number_format ($query['price'], 2). ' = &dollar;'.number_format($sub, 2). '<a href="cart.php?remove='.$id.'">[-]</a> <a href="cart.php?add='.$id.'">[+]</a> <a href="cart.php?delete='.$id.'">[Delete]</a> <br/> <br/> ';
}
}
$total += $sub + $shipping;
}
}
if ($total ==0) {
echo "Your cart is empty.";
}
else {
echo 'Total: &dollar;' .number_format($total, 2);
?>
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="upload" value="1">
<input type="hidden" name="business" value="youremail@outlook.com">
<?php paypal_items($db_conx); ?>
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="amount" value="<?php echo $total ;?>">
<input type="image" src="http://www.paypal.com/en_US/i/btn/x-click-but03.gif" name="submit" alt="Make payments with PayPal - it's fast, free and secure!">
</form>

<?php

}
}
?>

Hi if i have $date = "12-08-2018" or "2018-08-12"

Need to subtract a month. Could this be done for day and year even?

TIA

Desmond.

P.S.

What I want to do is clear out a database table with records over a month old so today is 27th Jan 2018. I would like to create a date “2018-12-01”

I can then use this in an SQL to delete all before “2018-12-01”

<?php
$var_Time = date("h:i:s");
$mysqli = new mysqli('localhost','root','blah','test');
if ($mysqli->connect_error) {
    die('Error : ('. $mysqli->connect_errno .') '. $mysqli->connect_error);
}
$insert_row = $mysqli->query("REPLACE  INTO test_table (id, time)  Values(NULL, '$var_Time')");
if($insert_row){
    while (false);
}else{
    die('Error : ('. $mysqli->errno .') '. $mysqli->error);
}
$mysqli->close();
?>

<?php
$mysqli = new mysqli('localhost','root','blah','test');
if ($mysqli->connect_error) {
    die('Error : ('. $mysqli->connect_errno .') '. $mysqli->connect_error);
}
$query = "SELECT * FROM `test_table`";
$result = $mysqli->query($query) or die($mysqli->error.__LINE__);
$var_set_time = stripslashes($row['time']);
$var_current_time = date("h:i:s");
$diff = strtotime( $var_current_time .' UTC' ) - strtotime( $var_set_time .' UTC');
echo $diff;
?>

$add ="<form action='cart.php' method='post'><input type='hidden' name='additem' value='$id'/><input type='submit' name='itemadd' onclick='CheckQty()' value='+'/></form>";
    $sub ="<form name='sub' action='cart.php' method='post'><input type='hidden' name='subitem' value='$id'/><input type='submit' name='itemsub' value='-'/></form>";

//add to quantity of item
    if (isset($_POST['itemadd'])){
    $additem = $_POST['additem'];
        if ($qty < 5){
        $addqty = $qty + 1;
        $adding = "UPDATE orders SET quantity = '$addqty' WHERE id = '$additem'";
        $add_query = mysqli_query($db_conx, $adding);
        header('Location: http://www.quichlicious.co.uk/cart.php');
        //print $additem;
        exit();
        }
        else
        {
        $usemes = "You have reached maximum quantity";
        }
    }
    //subtract to quantity of item
    if (isset($_POST['itemsub']) && ($_POST['itemsub'] !="")){
    $subitem = $_POST['subitem'];
            if ($qty > 1){
            $subqty = $qty - 1;
            $subing = "UPDATE orders SET quantity = '$subqty' WHERE id = '$subitem'";
            $sub_query = mysqli_query($db_conx, $subing);
            header("location: cart.php");
            exit();
            }
            else
            {
            $usemes = "<font color='red'>Please use delete to remove item</font>";
            }
    }