>To all of you experienced database designers.
>I am a self thought Database programmer, and since I did not followed any formal training some things are a little confusing still...
>What is the best way to update an inventory table? My question is if the correct approach is to do it each time a product is selected and processed, or to wait until the whole sale transaction (like a full invoice) is finished and do a 'bulk' update.

I expect that you will receive different answers due to the fact that there are different approaches but renders the same output.

We've been into Inventory/Accounting Systems for 8 years and so far, the most effective is that, we have a separate process per transaction to update inventory balance. Basically, the process will be called when transaction (one invoice) will be posted or finalized. Once it has been posted, the invoice can no longer be edited or deleted but can be cancelled which rolls back whatever updates made to related tables. At least, in our setting here, this approach is quite fit with the standard accounting practice.