Learn MsAccess 2

© Michael Brydon (brydon@unixg.ubc.ca)
Last update: 25-Aug-1997 Next Home Previous 1 o f 18
Access Tutorial 2: Tables
2.1 Introduction: The importance
of good table design
Tables are where data in a database is stored; consequently,
tables form the core of any database
application. In addition to basic data, Access permits
a large amount of domain knowledge (such as captions,
default values, constraints, etc.) to be stored at
the table level.
Extra time spent thinking about table design
can result in enormous time savings during
later stages of the project. Non-trivial changes
to tables and relationships become increasingly
difficult as the application grows in size
and complexity.
2.2 Learning objectives

How do I enter and edit data in the datasheet
view of a table?

How do I create a new table?

How do I set the primary key for a table?

How do I specify field properties such as the
input mask and caption?

Why won’t an autonumber field restart
counting at one?

What are the different types of keys?
2.3 Tutorial exercises
In this tutorial, you will learn to interact with existing
tables and design new tables.
Tutorial exercises 2. Tables
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2.3.1 Datasheet basics
• If you have not already done so, open the
univ0_v x.mdb database file from Tutorial 1.
• Open the Departments table. The important
elements of the datasheet view are shown in
Figure 2.1.
• Use the field selectors to adjust the width of the
DeptName field as shown in Figure 2.1.
• Add the Biology department (BIOL) to the table,
as shown in Figure 2.2.
• Delete the “Basket Weaving” record by clicking
on its record selector and pressing the Delete
key.
2.3.2 Creating a new table
In this section you will create and save a very basic
skeleton for table called Employees. This table
could be used to keep track of university employees
such as lecturers, department heads, departmental
secretaries, and so on.
• Return to the database window and create a new
table as shown in Figure 2.3.
• In the table design window shown in Figure 2.4,
type in the following information:
• Select File > Save from the main menu (or press
Control-S) and save the table under the name
Employees.
Field name Data type Description
(optional)
EmployeeID Text use employee
S.I.N.
FName Text First name
LName Text Last name
Phone Text
Salary Currency
Tutorial exercises 2. Tables
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FIGURE 2.1: The datasheet view of the Departments table.
The field names are shown in the “field
selectors” across the top of the columns.
The records are shown as rows.
The asterisk (*) indicates a
place holder for a new record. The grey boxes are “record selectors”.
The black triangle indicates the
“current record”.
The “navigation buttons” at the bottom of the window
indicate the current record number and allow you to go
directly to the first, previous, next, last, or new record.
You can temporarily sort the records
in a particular order by right-clicking
any of the field selectors.
Resize the DeptName column by clicking near
the column border and dragging the border to
the right.


Tutorial exercises 2. Tables
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FIGURE 2.2: Adding and saving a record to the table.
Add a new record by clicking in the DeptCode field
of the “new record” field (marked by the asterisk).

To permanently save the change to the
data, click on the record selector (note the
icon changes from a pencil to a triangle).

It is seldom necessary to
explicitly save new
records (or changes to
existing records) since
Access automatically
saves whenever you
move to another record,
close the table, quit
Access, etc.
Tutorial exercises 2. Tables
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FIGURE 2.3: Create a new table.
Click the New button to
create a new table.

Select “design view” (avoid using
the table wizard at this point). 
Tutorial exercises 2. Tables
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FIGURE 2.4: Use the table design window to enter the field properties for the Employees table.
The “description” column allows
you to enter a short comment
about the field (this information
is not processed in any way by
Access).
Enter the field names and
data types for the five fields.

The “field properties” section
allows you to enter information
about the field and constraints on
the values for the field.
Tutorial exercises 2. Tables
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2.3.3 Specifying the primary key
Tables normally have a primary key that uniquely
identifies the records in the table. When you designate
a field as the primary key, Access will not allow
you to enter duplicate values into the field.
• Follow the steps in Figure 2.5 to set the primary
key of the table to EmployeeID.
2.3.4 Setting field properties
In this section, you will specify a number of field
properties for the EmployeeID field, as shown in
Figure 2.6.
• Since we are going to use the employees’ Social
Insurance Number (S.I.N.) to uniquely identify
them, set the Field Size property to 11 characters
(9 for numbers and 2 for separating spaces)
• Set the Input Mask property to the following:
000\ 000\ 000;0
• Set the Caption property to Employee ID
FIGURE 2.6: Set the field properties for the
EmployeeID field.
Tutorial exercises 2. Tables
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FIGURE 2.5: Set the primary key for the Employees table.
Click on the grey box beside the field (or
fields) that form the primary key.

Either click the key-shaped icon in the tool bar or
select Edit > Primary Key from the menu. 
To select more than one field for use as the
primary key, hold down the Control key
while clicking on the grey boxes.
Discussion 2. Tables
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• Select View > Datasheet from the main menu to
switch to datasheet mode as shown in Figure 2.7.
Enter your own S.I.N. and observe the effect of
the input mask and caption on the EmployeeID
field.
• Select View > Table Design from the main menu
to return to design mode.
• Set the field properties for FName and LName
(note that Length and Caption are the only two
properties that are relevant for these two fields)
2.3.5 Using the input mask wizard
In this section, you will use the input mask wizard to
create a complex input mask for a standard field
type. You will also use the help system to learn more
about the meaning of the symbols used to create
input masks.
• Select the Phone field, move the cursor to the
input mask property, and click the button with
three small dots ( ) to invoke the input mask
wizard.
• Follow the instructions provided by the wizard as
shown in Figure 2.8.
• Press F1 while the cursor is still in the input mask
property. Scroll down the help window to find the
meaning of the “0”, “9”, “>” and “L” input mask
symbols.
2.4 Discussion
2.4.1 Key terminology
A key is one or more fields that uniquely determine
the identity of the real-world object that the record is
meant to represent. For example, there is a record in
the student information system that contains information
about you as a student. To ensure that the
record is associated with you and only you, it conDiscussion
2. Tables
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FIGURE 2.7: Observe the effect of the input mask and caption properties on the behavior of the
EmployeeID field during data entry
If a caption is specified, it replaces the
field name in the field selector.
Note that the input mask will not let you
type any characters other than numbers
from 0-9. In addition, the spaces between
the groups of numbers are added
automatically.
Input masks provide a relatively easy way to
avoid certain basic data input errors without
having to write complex error checking
programs. Note, however, that it is possible to
over-constrain a field so that users are unable to
enter legitimate values.
Try entering various characters and
numbers into the EmployeeID
field.


Press the Escape key when you are
done to clear the changes to the record. 
Discussion 2. Tables
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FIGURE 2.8: Use the input mask wizard to create an input mask.
Select “phone
number” from the
list of commonlyused
field types.


In Step 2, you may
edit the input mask
(e.g., remove the
area code section).

The items in this
list depend on the
“international
settings” specified
for Windows (e.g.,
“Zip Code” may
show instead of
“Postal Code”).
Since the input mask controls how
the information in the field looks, it
is possible to save some disk space
by storing the data without the
extras symbols, spaces, etc. For the
size of system we are building,
however, this savings is negligible.
Discussion 2. Tables
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tains a field called “student number” that is guaranteed
to be unique.
The advantage of using student number as a key
instead of some other field—like “student name”—is
that there may be more than one person with the
same first and last name. The combination of student
name and address is probably unique (it is
improbable that two people with the same name will
at the same address) but using these two fields as a
key would be cumbersome.
Since the terminology of keys can be confusing, the
important terms are summarized below.
1. Primary key — The terms “key” and “primary
key” are often used interchangeably. Since there
may be more than one candidate key for an
application, the designer has to select one: this is
the primary key.
2. Concatenated key: The verb “concatenate”
means to join together in a series. A concatenated
key is made by joining together two or
more fields. Course numbers at UBC provide a
good example of a concatenated key made by
joining together two fields: DeptCode and
CrsNum. For example, department alone cannot
be the primary key since there are many courses
in each department (e.g., COMM 335, COMM
391). Similarly, course number cannot be used as
a key since there are many courses with the
same number in different departments (e.g.,
COMM 335, HIST 335, MATH 335). However,
department and course number together form a
concatenated key (there is only one COMM 335).
3. Foreign key: In a one-to-many relationship, a
foreign key is a field (or fields) in the “child”
record that uniquely identifies the correct “parent”
record. For example, DeptCode and CrsNum in
the Sections table are foreign keys since these
two keys taken together are the primary key of
Discussion 2. Tables
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the Courses table. Foreign keys are identified in
Access by creating relationships (see Tutorial 3).
2.4.2 Fields and field properties
2.4.2.1 Field names
Access places relatively few restrictions on field
names and thus it is possible to create long, descriptive
names for your fields. The problem is that you
have to type these field names when building queries,
macros, and programs. As such, a balance
should be struck between readability and ease of
typing. You are advised to use short-but-descriptive
field names with no spaces.
For example, in Section 2.3.2 you created a field
with name FName. However, you can use the caption
property to provide a longer, more descriptive label
such as First name. The net result is a field name
that is easy to type when programming and a field
caption that is easy to read when the data is viewed.
In addition, you can use the comment field in the
table design window to document the meaning of
field names.
It is strongly recommended that you avoid all
non-alphanumeric characters whenever you
name a field or database object. Although
Access will permit you to use names such as
Customer#, non-alphanumeric characters
(such as #, /, $, %, ~, @, etc.) may cause
undocumented problems later on.
2.4.2.2 Data types
The field's data type tells Access how to handle the
information in the field. For instance, if the data type
is date/time, then Access can perform date/time
arithmetic on information stored in the field. If the
same date is stored as text, however, Access treats
it just like any other string of characters. Normally,
Discussion 2. Tables
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the choice of data type is straightforward. However,
the following guidelines should be kept in mind:
1. Do not use a numeric data type unless you are
going to treat the field as a number (i.e., perform
mathematical operations on it). For instance, you
might be tempted to store a person's student
number as an integer. However, if the student
number starts with a zero, then the first digit is
dropped and you have to coerce Access into displaying
it. Similarly, a UBC course number (e.g.,
335) might be considered a number; however,
since courses like 439B have to accommodated,
a numeric data type for the course number field is
clearly inappropriate.
2. Access provides a special data type called Auto
Number (Counter in version 2.0). An autonumber/
counter is really a number of type Long Integer
that gets incremented by Access every time
a new record is added. As such, it is convenient
for use as a primary key when no other key is
provided or is immediately obvious.
Since an autonumber is really Long Integer
and since relationships can only be created
between fields with the same data type, it is
important to remember that if an autonumber
is used on the “one” side of a relationship, a
long integer must be used for the “many” side.
2.4.2.3 “Disappearing” numbers in
autonumber fields
If, during the process of testing your application, you
add and delete records from a table with an autonumber
key, you will notice that the deleted keys are
not reclaimed.
For instance, if you add records to your Customer
table (assuming that CustID is an autonumber), you
will have a series of CustID values: 1, 2, 3… If you
Discussion 2. Tables
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later delete customer 1 and 2, you will notice that
your list of customers now starts at 3.
Clearly, it would be impossible for Access to renumber
all the customers so the list started at 1. What
would happen, for instance, to all the printed
invoices with CustID = 2 on them? Would they refer
to the original customer 2 or the newly renumbered
customer 2?
The bottom line is this: once a key is
assigned, it should never be reused, even if
the entity to which it is assigned is subsequently
deleted. Thus, as far as you are concerned,
there is no way to get your customers
table to renumber from CustID = 1.
Of course, there is a long and complicated way to do
it, but since used an autonumber in the first place,
you do not care about the actual value of the key—
you just want it to be unique. In short, it makes absolutely
no difference whether the first customer in your
customers table is CustID = 1 or 534.
2.4.2.4 Input masks
An input mask is a means of restricting what the user
can type into the field. It provides a “template” which
tells Access what kind of information should be in
each space. For example, the input mask >LLLL
consists of two parts:
1. The right brace > ensures that every character
the user types is converted into upper case.
Thus, if the user types comm, it is automatically
converted to COMM.
2. The characters LLLL are place holders for letters
from A to Z with blank spaces not allowed. What
this means is that the user has to type in exactly
four letters. If she types in fewer than four or
types a character that is not within the A to Z
scope (e.g., &, 7, %), Access will display an error
message.
Discussion 2. Tables
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There are a large number of special symbols used
for the input mask templates. Since the meaning of
many of the symbols is not immediately obvious,
there is no requirement to remember the character
codes. Instead, simply place the cursor on the input
mask property and press F1 to get help. In addition,
the wizard can be used to provide a basic input mask
which can later be modified.
2.4.2.5 Input masks and literal values
To have the input mask automatically insert a character
(such as a space or a dash) in a field, use a
slash to indicate that the character following it is a literal.
For example, to create an input mask for local telephone
numbers (e.g., 822-6109), you would use the
following template: 000\-0000;0 (the dash is a literal
value and appears automatically as the user
enters the telephone number).
The semicolon and zero at the end of this input mask
are important because, as the on-line help system
points out, an input mask value actually consists of
three parts (or “arguments”), each separated by a
semicolon:
• the actual template (e.g., 000\-0000),
• a value (0 or 1) that tells Access how to deal with
literal characters, and
• the character to use as a place holder (showing
the user how many characters to enter).
When you use a literal character in an input mask,
the second argument determines whether the literal
value is simply displayed or displayed and stored in
the table as part of the data.
For example, if you use the input mask 000\-
0000;1, Access will not store the dash with the telephone
number. Thus, although the input mask will
always display the number as “822-6109”, the number
is actually stored as “8226109”. By using the
Application to the assignment 2. Tables
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input mask 000\-0000;0, however, you are telling
Access to store the dash with the rest of the data.
If you use the wizard to create an input mask,
it asks you a simple question about storing literal
values (as shown in Figure 2.8) and fills
in the second argument accordingly. However,
if you create the input mask manually,
you should be aware that by default, Access
does not store literal values. In other words,
the input mask 000\-0000 is identical to the
input mask 000\-0000;1. This has important
consequences if the field in question is
subject to referential integrity constraints (the
value “822-6109” is not the same as
“8226109”).
2.5 Application to the assignment
You now have the skills necessary to implement your
tables.
• Create all the tables required for the assignment.
• Use the autonumber data type (counter in version
2.0) for your primary keys where appropriate.
• Specify field properties such as captions, input
mask, and defaults where appropriate.
If you create an input mask for ProductID,
ensure you understand the implications of
Section 2.4.2.5.
• Set the Default property of the OrderDate field
so that the current date is automatically inserted
into the field when a new order is created (hint:
see the Date() function in the on-line help system).
Application to the assignment 2. Tables
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• Do not forget to modify your Products table (the
data types, lengths, and field properties of
imported tables normally need to be fine tuned)
• Populate (enter data into) your master tables. Do
not populate your transaction tables.
For the purpose of the assignment, the term
“transaction” tables refers to tables that contain
information about individual transactions
(e.g., Orders, OrderDetails, Shipments,
ShipmentDetails). “Master”
tables, in contrast, are tables that either do
not contain information about transactions
(e.g., Customers) or contain only summary
or status information about transactions (e.g.,
BackOrders).