Expresion field to update to field in table

[Esrei]

I have created a query that minus cartons deliv from cartons shipped. I want
the result to update to a field in a table when I update a record

 

[John Vinson]

I have created a query that minus cartons deliv from cartons shipped. I want
the result to update to a field in a table when I update a record

Storing derived data such as this in your table accomplishes
three things: it wastes disk space; it wastes time (almost
any calculation will be MUCH faster than a disk fetch); and
most importantly, it risks data corruption. If one of the
underlying fields is subsequently edited, you will have data
in your table WHICH IS WRONG, and no automatic way to detect
that fact.

Just redo the calculation whenever you need it, either as a
calculated field in a Query or just as you're now doing it -
in the control source of a Form or a Report textbox.

If you have some GOOD reason to violate this practice, post
back... it can be done; it's just that ordinarily it shouldn't be.

John W. Vinson[MVP]

 

[Esrei]

Thank you, for the replies.

I will explain in detail: I have delivery note lines each with it's own ID.
The unit that must be counted is cartons. The whole line is not shipped at
once. A line can have 10 boxex that will be shipped in 3 shipments different
dates ex. I will have one user that records the delivery note and another
that does the shipments, when the shipment is done I want the the user to be
able to see how many cartons were delivered originaly (this is the easy part)
and how many is still avalable to be shipped. If the user decides to ship 3
cartons, and he fill in 3 in the shipment form, when he moves to a new record
in the form this must be updated?
Tanks for all the help.