Question

I have two tables. First table is Shipping with columns Product, Quantity and ID. Second table is Inventory with columns Product and Total.

I want to take the value of Shipping.Quantity and subtract it from the value in Inventory.Total WHERE the Product values match in each table and Shipping.ID is value in url ($onum). Then I want to set the new value as Inventory.Total for that product.

Best I could come up with:

UPDATE Inventory.Total 
CROSS JOIN Shipping 
SET Inventory.total=(Inventorytotal-Shipping.Quantity) 
WHERE Inventory.Product=Shipping.Product 
  AND Shipping.ID=$onum

Answer 1

UPDATE Inventory join Shipping 
ON Inventory.Product=Shipping.Product 
SET Inventory.Total=Inventory.Total-Shipping.Quantity
WHERE Shipping.ID=$ID