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From: Rob H on 21 Mar 2010 11:34
I have a table with a Gross Sales field and a Total Costs field, there is a
third field called Net Sales. How can I create a function to take Gross
Sales minus Total Costs to populate the Net Sales field? All three are set
to currency.
From: Al Campagna on 21 Mar 2010 15:29
Rob H,
In your table... you don't.
Since you have the GrossSales and the TotalCosts in your table, then you
can
always calculate NetSales "on the fly" in any form, query, or report.
= GrossSales - TotalCosts
As a general normalization rule... don't store any values in a table,
that can be
derived from data you already have.
--
hth
Al Campagna
Microsoft Access MVP 2007-2009
http://home.comcast.net/~cccsolutions/index.html

"Find a job that you love... and you'll never work a day in your life."

"Rob H" <RobH(a)discussions.microsoft.com> wrote in message
news:9CB96F6C-E68F-4D78-9844-C68B2A45ED08(a)microsoft.com...
>I have a table with a Gross Sales field and a Total Costs field, there is a
> third field called Net Sales. How can I create a function to take Gross
> Sales minus Total Costs to populate the Net Sales field? All three are
> set
> to currency.


From: John W. Vinson on 21 Mar 2010 16:39
On Sun, 21 Mar 2010 08:34:01 -0700, Rob H <RobH(a)discussions.microsoft.com>
wrote:

>I have a table with a Gross Sales field and a Total Costs field, there is a
>third field called Net Sales. How can I create a function to take Gross
>Sales minus Total Costs to populate the Net Sales field? All three are set
>to currency.

You don't.

The net sales should SIMPLY NOT EXIST in your table.

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; you can do so in a Query by
putting an expression like

NetSales: [Gross Sales] - [Total Costs]

in a vacant Field cell in the query, or on a Form or Report by putting

=[Gross Sales] - [Total Costs]

as the Control Source of a textbox.
--

John W. Vinson [MVP]
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