How to reduce item quantity when checking out a shopping cart in php?

Question

I'm doing a shopping cart system and I'm not sure how to reduce item quantity in mysql when checking out a shopping cart in php?

For example, when 2 of item1 are purchased, the quantity column in mysql should be reduced by 2. ie the quantity should be reduced with respect to the quantity purchased.

Answer 1

You can run a simple MySQL UPDATE query:

UPDATE `products` SET `quantity` = `quantity` - num_purchased WHERE `id` = 15

Obviously you'll need to replace the values, field names and table names with those you actually use...

Answer 2

See If you multiple products in cart, you should loop through product like below

foreach ($cartItem as $cart) {
    $productId = $cart['product_id'];
    $qty = $cart['qty'];
    $sql = "UPDATE `products` SET `num_of_stocks` = `num_of_stocks` - $qty 
            WHERE `id` = $productId";
}