Inventory stock levels

[Sagrado]

here is the thing


i am a student making a database for my alevels project

its a stock management database of a spare part stock room


can anyone here please explain to me how do i do this:

i need to know how to reduce the current stock number when in my form i type that part with a unique part number

for example the part number is 2323

in the form along with other info i enter part #2323 as the customer buys it

the current quantity in stock is 5 but when i enter it in the form i want it to get down to 4

how do i do this can anyone explain?


p.s i know i am not got at explaining my problem..ill attack a screen shot to help

[pbaldy]

I changed your meaningless title to something more helpful. As a rule it's not a good idea to store the quantity on hand. A discussion here:

http://allenbrowne.com/AppInventory.html

Tell your instructor it would break normalization rules. I've written stock management systems, and I calculate on hand from transactions.