MS Access for the Business Environment: Create a Calculated Field with the Expression Builder

About the Series …

This is the first article of the
series, MS Access for the Business Environment. The primary
focus of this series is an examination of business uses for the MS Access
relational database management system. The series is designed to provide
guidance in the practical application of data and database concepts to meet
specific needs in the business world. While the majority of the procedures I
demonstrate will be undertaken with Access 2002, many of the concepts
that we expose in the series will apply to numerous versions of MS Access.

As we progress through the series, we will build upon
previous lessons and the concepts we have introduced therein, in many cases.
However, one of my objectives is to make each lesson as "standalone"
as possible, in an attempt to prevent cases where one cannot complete a given
lesson without having components or objects that were created in previous
lessons. This should make it easier for "casual" visitors to join us
with any lesson, and still successfully complete that session, given an
existing understanding of concepts and principles that we have accumulated up
to that point.

To get the most out of the MS
Access for the Business Environment series, you will need to
have installed MS Access 2002, although, again, the majority of the
concepts we take up will certainly apply to earlier versions. Make sure that
the PC that you plan to use meets the system requirements, including
hardware and operating systems, of MS Access, as well.

Introduction to this Tutorial

This tutorial will
introduce calculated fields in MS Access. We can use calculated fields
both in queries and tables; here, we will focus upon their creation and use in
general. This lesson will include:

• A brief introduction to calculated fields;
• An introduction to the MS Access Expression Builder;
• A practical walkthrough of the process of creating a
  calculated field.

Let’s begin by discussing the reasons we might want to
create a calculated field and how such a component can help us to extend the
power of our Access databases.

Introduction to Calculated Fields

Many occasions arise in the design of a database where
calculated fields are useful. The most common scenario surrounds fields that
contain derived data–that is, fields that are made up of data that
already exists elsewhere in the database. An example might be the net price of
a product that an organization sells, after discounts. A table under
consideration might house the retail price and the discount information, but
the net price, or retail price less the discount, is a derived amount. We can
more efficiently meet a business need for the net price by installing a
calculated field that would provide the information as needed.

Using the Expression Builder to
Create Calculated Fields

Let’s open the Northwind sample
database, and begin by creating a rudimentary calculated field. We will use the
Expression Builder, which can often assist us in the creation of
expressions when we are learning about expressions, and perhaps Access, in
general. We could also enter the expressions directly, if we were certain of
the syntax required and how to add it, but for now, we will use the Expression
Builder.

We will start Access and proceed,
taking the following steps:

Access
opens, and, depending upon whether you have opened it before, may display an
initial dialog. If so, close it.

The
main switchboard appears as shown in Illustration 2.

We
arrive at the Database Window, which appears as depicted in Illustration
3.