Microsoft Access Lesson 3

Lexington Technology Center

February 18, 2003

Bob Herring

On the Web at www.lexington1.net/AdultEd/computer/microsoft_access.htm

Access Lesson 3Review of Thursday’s Lesson

• Template Databases• Database Wizard• Switchboard Forms• Forms and Controls• Reports• Database Window

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Access Lesson 3Relationships

• Tables can be related if they have a field in common. Access uses the relationship to create information by matching the fields and reporting the results.

• There are 3 types of relationships:

• One-to-many: Each record in the primary table can be associated with many records in the related table

• One-to-one: Each record in the primary table can be associated with only one record in the related table

• Many-to-many: More than one record in the primary table can be associated with many records in the related table 3

Access Lesson 3Relationships in Access

• The table on the “one” side of the relationship is called the parent table. The other table is called the child table.

• How the 3 types of relationships are created in Access:

• One-to-many: The common field in the parent table is called the primary key, and the related field in the child table is called the foreign key.

• One-to-one: The common fields are both primary keys.

• Many-to-many: Ordinarily not possible, but in Access two one-to- many relationships can be joined to create this kind of relationship.

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Access Lesson 3One-to-Many Relationships

ParentTable

PrimaryKey

ForeignKey

ChildTable

Relationship Line

• In this example, one category can encompass many products

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Access Lesson 3One-to-One Relationships

• These two tables have a one-to-one relationship because they concern the same subject: employees

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Access Lesson 3Many-to-Many Relationships

JunctionTable

• Since many orders might call for many products, a junction table is used to avoid violating referential integrity.

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Access Lesson 3Referential Integrity

• Optional series of rules that guarantees that relationships will be valid.

• Every record in a child table (the “many” side) must have one and only one record in the parent table (the “one” side)

• No child record can be entered without a parent• No parent record can be deleted if it still has children• No child record’s foreign key can be changed without a match in the parent table• No parent table’s primary key can be changed if there are child records

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Access Lesson 3Referential Integrity, Continued

ReferentialIntegrityEnforced

• What you need to enforce referential integrity in Access:• The matching field in the parent table must be the primary key• Relating fields must be the same data type• Both tables must be in the same database -- OR, if using linking fields, both tables must be in Access and the linked table’s database must be open

• Referential integrity is indicated by 1 - on the relationship line

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Access Lesson 3Referential Integrity, Continued

Edit Relationship

• Referential integrity is set by editing the relationship• Right-click the relationship line and select Edit Relationship • Click the “Enforce Referential Integrity” check box

Enforce Referential Integrity

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Access Lesson 3Referential Integrity, Continued

Cascade Delete

• If referential integrity is selected, you can also choose to have Access automatically update or delete records• Cascade Update and Cascade Delete maintain referential integrity by changing child tables to match changes in the parent table

• Beware of Cascade Delete!! This could lead to loss of data!• Cascade Update has no effect if you are using a primary key since you cannot change an autonumber

Cascade Update

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Access Lesson 3Joins

InnerJoin

RightOuter Join

LeftOuter Join

Left Right

• A join is a control that tells Access which records to select when running a query.• Inner joins are the most common.• Outer joins include all records from one of the tables and records from the other when the joined fields match.

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Access Lesson 3Address Book Relationships

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Access Lesson 3Asset Tracking Relationships

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Access Lesson 3Contact Management Relationships

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Access Lesson 3Event Management Relationships

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Access Lesson 3Expenses Relationships

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Access Lesson 3Students and Classes Relationships

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Access Lesson 3Inventory Control Relationships

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Access Lesson 3Ledger Relationships

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Access Lesson 3Resource Scheduling Relationships

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Access Lesson 3Time and Billing Relationships

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Access Lesson 3Membership Relationships

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Access Lesson 3Order Entry Relationships

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Access Lesson 3Book Collection Relationships

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Access Lesson 3Music Collection Relationships

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Access Lesson 3Form Wizard

• In the Northwind database, select the “Forms” tab• Click the “New” button

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Access Lesson 3Form Wizard

• In the “New Form” dialog box, click “Form Wizard”• Choose the Products table to begin, then click “OK”

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Access Lesson 3Wizard, Step 2 -- Data Fields

• Step 2 is to choose fields from the available tables and queries• Click the right arrow to select the desired fields, or• Click the double right arrow to select all

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Access Lesson 3Choosing Fields for a Form

• Select “ProductName”, “SupplierID”, “UnitsinStock”, and “Discontinued”• Choose “Next”

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Access Lesson 3Wizard, Step 3 -- Layout Style

• In Step 3, select a layout style for the form• Click through the four choices to preview the different styles• Click “Next”

Columnar Tabular

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Access Lesson 3Wizard, Step 3 -- Layout Style

• In Step 3, select a layout style for the form• Click through the four choices to preview the different styles• Click Next

Datasheet Justified

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Access Lesson 3Wizard, Step 4 -- Background Style

• In Step 4, select a background style for the form• Click through the choices to preview the different styles

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Access Lesson 3Wizard, Step 5 -- Finish

• To finish the form, give it a name and click “Finish”• Click the radio button to open the form after creating it

Openthe Form

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Access Lesson 3Automatic Form in Action

• The new form displays a portion of the information in the table• Forms are two-way -- they display information, but also guide data entry

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Access Lesson 3Adding a New Product

• Click the “New Record” button• Notice that the “Supplier” field is lit -- this is referential integrity in action -- every product must have a supplier!

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Access Lesson 3Adding a New Product

• After choosing a supplier, enter the name of the new product• Enter the number of units in stock• Data entered in the form is immediately saved in the database

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Access Lesson 3Review

• Relationships• Referential Integrity• Joins• Template Database Relationships• Automatic Forms

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