2. Data Types
Data type Description
Auto Number Automatically generates a
number each time you add a
record, it is used as a unique
identifier for each record.
Text Stores letters, numbers and
any combination. Can be up to
255 characters in length.
Memo This is a really big text field/ It
can hold up to 64,000
characters.
Number Holds numbers and decimal
points but nothing else. Set a
field as number if you wish to
do calculations.
Currency Formats money fields.
3. Data Types cont.
Data type Description
Date/Time Either the date or the time or
even both, in a variety of
formats.
Yes/No For fields where one of the
two answers is required.
OLE Object You can add photographs,
sounds etc. in a field of this
data type.
Hyperlink For webpage addresses.
Lookup Wizard Prevent errors by presenting
the user with answers to
choose from.
4. Field Properties
Property Description
Field Size Used to fix the maximum
length of a text field which is
255 characters.
Format This fixes how data can be
displayed, for example dates
can be displayed in many
different forms such as
13/01/01 or 13 jan 01
Input Mask This sets a pattern for the data
to be entered into this field.
Caption This is the field label in a form
or report.
5. Field Properties cont.
Property Description
Default Value The value entered into the
field when the record is
created. It is usually left blank
but can be very powerful.
Validation Rule This defines the data entry
rules.
Validation Text This is the error message if
data is invalid.
Required Indicates whether an entry
must be made or not.
Indexed This allows data to be stored
in the order of this field, which
speeds up searches.
Allow zero length Used with text fields to decide
whether records in that field
are allowed to contain zero
length or empty text strings.
6. Field Properties cont.
Property Description
Unicode compression Method of compressing the
data entered into this field.
IME Mode Input method editor, which
allows special character input.
IME Sentence Mode Allows special character input.
7. Formats
• You can use a format if you want to change the way your data appears on
screen.
• Each field type has its own set of formats. Some of the most commonly
used are as follows:
Text and Memo Formats
Symbol Meaning What it does
> Greater than Makes all text
appear in upper
case
< Less than Makes all text
appear in lower
case
8. Formats cont.
Currency Formats
General Number Default option
Currency Displays numbers as currency
Fixed Locks the field to display a
specified number of decimal
places.
Standard Adds a thousands separator.
Percent Displays decimal places as a
percentage.
In a number field, you can change the Field Size setting from Long Integer to Single if you
want to dispense with decimal places. However, if the field is part of a relationship, you
should be aware that an AutoNumber field must be set to Long Integer.
9. Formats cont.
Date/Time formats
You have a choice of how the date/time is displayed
Yes/No Formats
You have three initial choices, which are Yes/No, True/False and On/Off. You can add your own selections to
this list.
The Default Field Property
Default values are added automatically when you add a new record. For example in a table of names and
addresses you might set the Town field Brighton. Brighton then appears automatically each time a new
record is added and the user can either leave it or change it to something else.
You can also use expressions in this field property. Typically =Date() will return the current date from your
PC.
In a Library Book Loaning System the default value for the Date of Loan field could be set to =Date() and ,
similarly for the Date of Return the default value could be set to =Date()+14 (assuming a 14-day loan period).
10. Validation and Required Fields
Validation tests and required fields are your weapons in the war against bad data.
Using the Required property is easy because there are only two choices – yes and no. Set the
Required property to Yes if you want to force the user to enter something in this field.
Setting Validation Rules
The Validation property is more sophisticated because it performs a test on incoming data to
make sure it’s what you want.
Two properties require your attention:
Validation Rule Test that will be applied to the
data.
Validation Text Message which ACCESS will
display if the data is
unacceptable.
11. Validation and Required Fields cont.
• Validations work best with number, currency and date fields because the incoming data is
more predictable. An Expression is an instruction that you give to Access in a language that
Access can understand. For example, if you want to force users to enter only positive
numbers in a number field, the expression is “> 0” i.e. the number must be greater than zero.
Operator Meaning
>0 Must be greater than zero
<>0 Cannot be zero
>=5 Greater than or equal to 5
>=0 And <=100 Must be between 0 and 100
<=0 Or <=100 Must be less than 0 or greater than 100
>=Date() Must be todays date or later
>=Date() Or Is Null Must be todays date or later or blank
>=#1/1/96# And <#1/1/97# Must be a date in 1996
Like “A????” Entry must contain the letter A
12. • To write a validation rule, you can either write the rule yourself, or you can use the
Expression Builder. To start the Expression Builder, click the Build button that
appears when you select the Validation Rule Property.
The Expression Builder helps you to write expressions. It lists functions and operators
that you can use. It can also prompt you to remind you what to do next and it will
stop you making common mistakes.
13. Example Possible validation text
>8000 Please enter a salary greater
than £8000
<#01/01/01# You must enter dates before
jan 1st 2001
>Date() The date returned must be
after todays date
‘S’ or ‘M’ or ‘L’ Sizes can only be S, M or L
Between 0 and 36 Goals scored cannot be
greater than 36
<20 Age of student must be less
than 20
IN(‘A’, ‘B’, ‘C’) Grades must be A, B or C
14. Input Masks
The aim of an Input Mask is to prevent the user entering bad data and to
remove data inconsistencies from occurring. The great danger in using them
is that you might end up preventing the user from entering correct data. For
this reason, you must think carefully before deciding to set an input mask for
a field.
Input masks make data entry easier. They display on screen a pattern for the
data to be entered into the field.
An input mask is a series of characters, which tells Access what kind of data to
expect. Each field can have an input mask, with the exception of a memo
field.
They are suitable for data that always has the same pattern s such as phone
numbers, national insurance numbers and postal codes.
You can either write your own input mask or you can use the Wizard. To use
the Wizard, click the Build button, which appears when you click the Input
Mask Property.
15. Characters for input masks you are likely to use
are as follows:
0 A number (0-9 must be entered)
9 A number (0-9 may be entered)
# A number, + or- sign or space may be
entered
L A letter A-Z must be entered
? A letter A-Z may be entered
A A letter or digit must be entered
a A letter or digit may be entered
C Any character or space may be
entered
& Any character or space must be
entered
< All characters to the right are
changed to lower case
> All characters to the right are
changed to upper case
16. Examples of Input Masks
A National insurance number in the UK must be of the form AB123456C. All letters are in
capitals. Its input mask would be >LL000000L (it must be two letters followed by six numbers
and one letter).
A postcode consists of one or two letters, then one or two numbers, then a space, a number
and two letters. All the letters must be capital letters. Examples are B1 1BB or DE13 0LL. The
input mask would be >L?09 0LL.
Car Registration numbers such as FN03 ANJ would have >LL00 LLL as an input mask.
F2 Select an entire field
Ctrl+; Insert the Current Date
Ctrl+: Insert the Current Time
Ctrl+Enter Insert a Line Break (use it in a memo or large text field)
Ctrl++ Add New Record
Ctrl+- Delete the Current Record
Shift+Enter Save the Record
Ctrl+Z Undo the last change you made (don't rely on this)
Ctrl+Enter Open the selected object in Design View
Alt+F4 Quit Access
