Exploring MicrosoftAccess 2003

Chapter 6

Many-to-Many Relationships:

A More Complex System

Objectives

• Define and explain a many-to-many relationship• Use cascade Update and Cascade Delete• Explain how AutoNumber field simplifies entering new

records (Autonumber is compatible with long integers) • Create a main and subform based on a query• Create a parameter query• Use aggregate function• Use Get External Data command

Overview

• More database design practice• Extends relational database concepts• Use AutoNumber to simplify record creation• Extends subform and query information for

related tables• Create a parameter query• Create queries with built-in aggregate function

Case Study: Computer Super Store

• A relational database with more than two tables

• Finding information becomes more difficult unless you use a database

• Many-to-many relationship implemented by a pair of one-to-many relationships

Case Study: Computer Super Store

• Combined keys necessary when a pair of one-to-many relationships is built into a separate table

• Using the AutoNumber field type keeps order• Relationships window shows visual relationships• Enforce referential integrity

Implementing Many-To-Many Relationships

Enforce ReferentialIntegrity is selected

Many-to-manyRelationship is implementedby a pair of one-to-man relationships

Relationships and Referential Integrity

Hands-On Exercise 1

• Add a Customer• Create the Relationships• Delete an Order Details Record• Edit a Relationship• Delete a Record in the Orders Table

Subforms, Queries, and AutoLookup

• Main and subforms based on queries:– display information from multiple tables– display records other than by primary key

• AutoLookup will find corresponding data after unique ID is entered

Main Form and Subform

Main form has fieldsfrom Consultants table

Subform has fieldsfrom Client table

Designing a main and subform

Main formdetail

Subformdetail

Subforms and Multiple Table Queries

Hands-On Exercise 2• Create the Subform Query• Test the Query• Create and Modify the Orders Form• Change the Column Widths• Enter a New Order• Print the Completed Order

Advanced Queries

• Parameter query prompts for criteria when executed• Total queries performs calculations on a group of

records• Total row – Contains either Group by or aggregate entry• Group by – Records in the dynaset are to be grouped

according to the like values• Sum Function – Specifies math to performed on that

field for each group of records

Parameter Query

Run button

Table row indicatesTable from whicha field comes

Enter prompt issquare brackets

Advanced Queries

Hands-On Exercise 3• Create the Query• The Report Wizard• Modify the Report Design• Print the Report• Copy an Existing Query• Create and Run a Total Query• Create a Parameter Query• Exit Access

Expanding the Database

• Existing tables are unaffected by adding a fifth table

• Use parameter query to calculate data• Use Get External Data command to import a

table from another database

Adding Tables

Existing tables andrelationships areunaffected by additionof new tables

Expanding the Database

• Hands-On Exercise 4• Import the Salesperson Table• Modify the Orders Table Design• Add the Salesperson to Existing Orders• Create a Relationship• Modify the order with Customer Information Query• Modify the Order Form• The Completed Order Form• Database Properties

Chapter 6 Summary (1 of 2)

• A many-to-many relationship requires an additional table

• Many-to-many is implemented with a pair of one-to-many relationships

• Enforce referential integrity to prevent errors

• Base forms and subforms on queries

Chapter 6 Summary (2 of 2)

• Parameter query uses prompts• Aggregate functions perform calculations on

groups of records• New tables may be added at any time without

affecting data in the existing tables

Practice with Access

1. Sales Commission2. Find products that have never been ordered3. Super Store Customer Form4. Add Command Button to Order Form5. Final Super Store Order Form6. The Switchboard7. The Startup Property

Case Studies

• Medical Research

• The Stock Broker

• The Video Store

• Class Scheduling

• Career Planning and Placement