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42 CHAPTER 3 USING ACCESS TO IMPLEMENT A RELATIONAL DATABASE

Table 3-1 Field Properties in Access

Field Property Description

Field Size Sets the maximum size for data stored in a Text, Number, or
AutoNumber field. In a Text field, the default size is 50, but the size
may range from 1 to 255. In Number fields, the default is set to
Long Integer.
Format Specifies how data are to be displayed in a field. Particularly useful
in specifying the format for numbers, currency, dates, and times.
Decimal Places Specifies the number of digits allowed to the right of the decimal
point. Auto allows the Format property to determine the number of
decimal places automatically.
Input Mask Makes data entry easier by adjusting the data entered so that it con-
forms to the standard set in the Input Mask. Also used to control the
values users can enter. Review the InputMask property help screen
to familiarize yourself with this property. See Steps 6-8 below.
Caption Specifies the text for labels attached to controls created by dragging
a field from the field list, and serves as the column heading for the
field when the table or query is in Datasheet view. Captions should
be descriptive of the Field Names they relate to since they will be
used as headings for the data in creating Forms and Reports.
Default Value Specifies a default value for a field (e.g., San Jose can be set as the
Default Value for a City field; the user then has the option of accept-
ing the Default Value or inputting different data).
Validation Rule Specifies the requirements and limits the values allowed for data
entry. For example, the Validation Rule may begin with the word
"Like" and continue on with a series of characters placed in quotes
to set the requirements for data to be entered into the field. The
mean!ng of these characters is found under the Input Mask Syntax
and Examples help screen. Review the Validation Rule property help
screen to familiarize yourself with this property.
Validation Text The text input in the Validation Text property specifies the message
to be displayed to the user when the Validation Rule is violated. For
example, when a record is added for a new employee, you can
require that the entry in the Start Date field fall between the compa-
ny's founding date and the current date. If the date entered isn't in
this range, you can display the message: "Start date is incorrect."
Required Specifies whether or not a value is required in a field; if Yes, the
field requires a value, if No, no entry is required.
Allow Zero Length Indicates whether an empty string (i.e., a string containing no char-
acters) is a valid entry; if Yes, the field will accept an empty string
even when the Required property is set to Yes.
Indexed This sets a single-field index (i.e., a feature that speeds the sorting and
searching of a table by allowing the program to do a speed search on
the field). The primary key is always indexed. When a field is indexed,
it is also necessary to specify whether duplicates will be allowed. For
example, when creating a purchase table, the primary key might be
Purchase# and you would not want to allow duplicates. However,
when creating a table to add the inventory purchased on a particular
purchase, you might still want to be able to sort and search based
·upon the Purchase# (which would require that field to be indexed), but
you wo'uld expect that a particular purchase might have several items
of inventory. Therefore, duplicates would be allowed.