Exploring Microsoft Access

Chapter 5One-to-Many Relationships:

Subforms and Multiple Table Queries

• One-to-many relationship essential in database design

• Use the Relationships window

• Define referential integrity

Objectives (1 of 2)

• Distinguish between a main form and a subform

• Create a query based on multiple tables

• Create a main form with two subforms

Objectives (2 of 2)

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

• Main forms and subforms created from related tables.

• Reports based on a multiple-table query

Overview (2 of 2)

Relationships WindowCustomerID is primary keyin Customers table

Relationship line

CustomerID is foreign key in Loans table

Enforce ReferentialIntegrity

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 displayrelated 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 the tableor query forthe form

Select all fieldsto add to the form

Step 1

Step 2

Form Wizard (2 of 4)

Step 3

Select the tableor query forthe subform

Select all fieldsto add to the subform

Form Wizard (3 of 4)

Step 4

Step 5

Choose how to displaythe form and subform

Form Wizard (4 of 4)

Choose the style

Enter a name for the form and the subform

Step 6

Step 7

Subform

CustomerC01

Loans forCustomer C01

Status bar forLoans 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

Enter criteria

Select table

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 forCustomer C01

Payments forLoan 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