Microsoft Office Tutorials and References
In Depth Information
Refining Your Table in Design View
Table 2-2 (continued)
Data Type
What It Holds
When to Use It
Yes/No
Binary data such as
Yes/No , Male/
Female , and
True/False .
When you have a field that can
have only one of two entries. This
data type appears as a check box
on the datasheet; it can appear as a
check box, option button, or toggle
button on forms; it can be either on
or off. Use the Format field
property to define the values, such as
True/False , Male/Female , or
Available/Discontinued .
Hyperlink
URLs, e-mail
addresses, and
other types of links.
When you want to link to a web
page, e-mail address, or file. We
cover hyperlinks in Chapter 1 of this
minibook.
Attachment
One or more
attachments (files).
When you want to store a file
as part of a record. We cover
Attachment fields in Chapter 1 of
this minibook.
Calculated
Defined by an
expression
(calculation).
When you want to calculate a result
by using other fields in the table.
Calculations are covered in short
in Chapter 1 of this minibook and in
detail in Book III, Chapter 2.
Lookup Wizard
Not really a data
type. This option
runs the Lookup
Wizard.
When you want to select a data
from another source to fill a field,
such as when you want to select
state abbreviations in a list or
choose products for an order from
that products you actually stock.
AutoNumber fields have one purpose: to act as the primary key field for
tables that don’t have an existing field to uniquely identify records. Don’t
use AutoNumber fields for anything else. In fact, most Access database
designers use AutoNumber fields to create primary key fields — and then
make sure that those key fields never appear on forms and reports.
Here’s why the key fields are often hidden: You have no control of the
numbers that Access issues when numbering your records. If you start adding
a record and then cancel it, Access may decide that particular number is
already used and skip it the next time you add a record. You can’t change an
AutoNumber field’s value. If you need a series of numbers to not end up with
holes (skipped numbers), don’t use an AutoNumber field.
 
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