Entry of Value to a Field In One Table That Gets Subtracted From A Field in a Related Table

[roybb]

Hi Everyone,



So I have 2 tables. The first table "Customer" contains a field "Total Minutes Remaining on Contract ". The Second table (related) "Customer Session" has a field called "Contract Minutes Used".

What I want to do is have it so that when I enter in the total amount of contract minutes used in a session it is automatically subtracted from the "Total Minutes Remaining on Contract" field.

Can anyone make any suggestion as to how I might accomplish this?

Thanks!

[June7]

Saving this calculation to table is bad idea and poor db design. Calculate the balance when needed.

Do an aggregate query that sums the minutes used grouping on the customer. Then join that query to the Customer table.

Access Help has guidelines on building aggregate query.

Since customers could have multiple contracts over time, really should have a Contracts table.

Did you review the link I referenced in your other thread?