Hello again have another problem looking for help with



I got my Database all squared away with everything in one table now and normalized as much as I can. what I am trying to do now is when I enter a customer order I can have an on-update event subtract from my current inventory level for that product.

Here are the two tables

Products table named All Products

product_id (PK)
Name
categories
quantity

Order Table named Orders
Order_ID (pk)
Customer_ID
Product_ID
Quantity
Cost

What I want to do is have the value I enter into quantity for the order subtract from the quantity in the all products table.

Relasionships between ID fields have been set already and are working. I am the only one who will use this database so I don't need anything fancy just a simple update but I do not know where to start