Exploring Microsoft Access Chapter 5 One-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 Window CustomerID is primary key in Customers table Relationship line CustomerID is foreign key in Loans table Enforce Referential Integrity

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 the table or query for the form Select all fields to add to the form Step 1 Step 2

Form Wizard (2 of 4) Step 3 Select the table or query for the subform Select all fields to add to the subform

Form Wizard (3 of 4) Step 4 Step 5 Choose how to display the 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 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 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 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