Access-5.ppt 610KB Mar 29 2010 04:55:15 AM

Exploring Microsoft Access
Chapter 5
One-to-Many Relationships:
Subforms and Multiple Table Queries

Objectives (1 of 2)
• One-to-many relationship essential in
database design
• Use the Relationships window
• Define referential integrity

Objectives (2 of 2)
• Distinguish between a main form
and a subform
• Create a query based on multiple tables
• Create a main form with two subforms

Overview (1 of 2)
• The real power of Access: one-to-many
relationships between tables
• Primary key of one table is foreign key of

the related table
• Referential integrity ensures consistency
between tables

Overview (2 of 2)
• Main forms and subforms created from
related tables.
• Reports based on a multiple-table query

Relationships Window
CustomerID is primary key
in Customers table

Relationship line

Enforce Referential
Integrity
CustomerID is
foreign key in
Loans table

Referential Integrity (1 of 2)
• Access automatically implements a form of
data validation during data entry
• Can enter a record in the “one” table, but
not in the “many” table if record contains
an invalid value for the foreign key
• This ensures related tables are consistent
with one another.

Referential Integrity (2 of 2)
Delete Record button

Click + to display
related records
(subdatasheet)

Cannot delete a Customer without first deleting related Loan

Subforms

• Subform is a form within a form
• Main form would be based on primary table,
while subform is based on related table
• Use Subform Wizard
• Can be created either on main form or
dragged from a separate form

Form Wizard (1 of 4)
Select all fields
to add to the form

Step 1

Select the table
or query for
the form
Step 2

Form Wizard (2 of 4)
Select the table

or query for
the subform

Step 3

Select all fields
to add to the subform

Form Wizard (3 of 4)
Choose how to display
the form and subform

Step 5

Step 4

Form Wizard (4 of 4)
Enter a name for the
form and the
subform

Step 6
Choose the
style
Step 7

Subform
Customer
C01

Loans for
Customer C01

Status bar for
Loans form

Status bar for Customers form

Multiple Table Queries
• Query information from two tables

• Create a select query using both tables
• Query window displays selected fields of
each table

Multiple Table Queries
Column selector

Select table
Enter criteria

Multiple Subforms (1 of 2)
• A main table can have multiple levels of
subforms
• Useful for displaying a one-to-many
relationship within a one-to-many
relationship

Multiple Subforms (2 of 2)
Customer C01

Loan L031 for
Customer C01

Payments for
Loan L031

Chapter 5 Summary (1 of 2)
• Access database may contain multiple tables
• Each table has a primary key which is the foreign
key of a related table
• Relationships window to create one-to-many
relationships
• Referential integrity ensures consistency between
related tables

Chapter 5 Summary (2 of 2)
• Subform is a form within a form
• A main form can have multiple subforms
• Select query can include fields from several
tables

• Tables can be added at any time without
disturbing existing data