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Chapter 1 & 2Relational Databases and Queries

CS101 WVU

Working with Table Views

• Datasheet View• Design View

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Design View

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Datasheet View

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Using Forms, Queries and Reports

• Tables– Primary Key

• Forms• Queries– Criteria

• Reports

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Tips on Database Management

• Database files should be named using meaningful names

• Database files should be stored in meaningful folders and subfolders

• Back up your files!

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Compacting & Repairing a Database

• Access databases increase in size over time

• Compacting – Avoids loss of data– Recovers unclaimed space– Defragments fragmented databases– Repairs corrupt databases

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Steps in Compacting & Repairing and Backing-up Your Database

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Back UpDatabase option

Backing Up a Database• Backups are critical to a database • Access provides a default file name,

including the original file name and adds on the current date

• Default extension for Access databases is accdb

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Creating Relationships• A common field—used to relate two tables

together• Join lines—allow relationships between two

tables to be created on a common field• Three types of relationships used by Access

to manage relationships between tables:– Enforce referential integrity– Cascade update related fields (see Chapter 2)– Cascade delete related records (see Chapter 2)

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Using the Relationships Window

• Relationships should be created after the tables are created, but before any data is entered

• Relationships between tables are represented by join lines in the Relationships window

• Most common method of connecting two tables is using a primary key from the primary table to the foreign key in the related table 11

Referential Integrity• Ensures that data cannot be entered into a

related table unless it first exists in the primary table

• Example:– Banks would not want to offer a loan to an

individual unless that individual was already established as a customer of the bank.

– Thus, the customer has to be entered into the customer table, before a new loan can be made in the loan table with that customer’s ID.

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Relationships Window

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Table Design: Designing Data

• Table Definition – Revised• Input vs. Output in Design

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Designing Fields Guidelines

1. Include the necessary data2. Design for now and the future3. Store data in its smallest parts4. Add calculated fields to a table5. Design to accommodate date

arithmetic6. Link tables using common fields

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Include Necessary Data• Determine what data is necessary• Create a rough draft of reports that

may be needed• Create tables based on fields

necessary for reports

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Design for Now and the Future

• Organizations evolve over time• Databases should evolve with the

organization– Anticipate future needs of the

organization– Build flexibility into system to satisfy

future needs

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Store Data in Smallest Possible Pieces

• Creating a name field with the entire name in it violates good database design and reduces the usefulness of the data

• Divide data into the smallest pieces that you’re going to need to access– Example: Prefix, FirstName, LastName,

Suffix• Provide flexibility for the user

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Calculated Fields in a Table

• Produce a value from an expression or function that references one or more existing fields

• Access 2010 allows the user to store calculated fields– Can be a benefit or a potential problem– Exercise caution when using calculated

(derived) fields

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Design to Accommodate Date Arithmetic

• Calculated fields can also create date/time data

• Plenty of examples available for using date/time date arithmetic

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Link Tables Using Common Fields

• Tables may be joined based on a common field

• Join lines are created –Manually by the user, or – Automatically by Access when two fields in

separate tables share the same name between two related tables

• Avoid Data redundancy errors– The unnecessary storage of duplicate data in

two or more tables

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Creating Tables• Create fields in Design View• Import data from another database

or application– Examples: Excel spreadsheets or Word

text files• Enter data directly into rows in

Datasheet view

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Creating Fields in Tables• Field names should be meaningful• Rules for naming fields:– Length can be up to 64 characters– Can include letters, numbers and

spaces– Access uses CamelCase notation• Use uppercase letters for each first letter of

each new word• Example: ProductCost

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Field Data Types• Every field has a data type • Determines:– The type of data that can be entered – The operations that can be performed

on that data• Access recognizes 10 data types

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Access Data Types• Number• Text• Memo• Date/Time• Currency• Yes/No

• OLE• AutoNumber• Hyperlink• Attachment

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Foreign Key Review A field in one table that is also a

primary key of another table

SpeakerID is the primary key of the Speakers

SpeakerID is the foreign key in the SessionSpeaker table (duplicates are allowed)

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Using Table ViewsDatasheet View

Active record

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Using Table Views• Design View• PivotTable• PivotChart

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Work with Field Properties

• Field property• Text data type• Number data type• Caption property• Validation rule

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Access Field Properties• Field Size• Format• Input Mask• Caption• Default Value• Validation Rule• Validation Text

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Access Field Properties (continued)

• Required• Allow Zero Length• Indexed• Expression• Result Type

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Understanding Table Relationships

• Efficiently combine data from related tables

• Create queries, forms, and reports

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Establishing Referential Integrity

• Edit Relationships dialog box

• Select Enforce Referential Integrity checkbox

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Set Cascade Options• Cascade Update Related Fields• Cascade Delete Related Records

Click Cascade Delete with caution

Click Cascade Update incase the primary key changes

Click Enforce Referential Integrity

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Options on External Data Tab

• Import & Link• Export• Collect Data• Web Linked Lists

External Data TabClick Excel to importspreadsheet data

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Import Data from Excel

Click Browse to finda spreadsheet

Decide what you wantto do with the data

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Import Data from Excel (continued)

Choose the worksheetto import

Preview of theworksheet data

Click Next to continue

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Import Data from Excel (continued)

Column headings

Click Next to continue

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Import Data from Excel (continued)

Change Indexed property to Yes (No Duplicates)

Click Next to continue

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Import Data from Excel (continued)

AID becomes the primary key

Click Next to continue

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Import Data from Excel (continued)

Accounts becomes thetable name

Click Finish to import the data

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Types of Relationships• One-to-one relationship• One-to-many relationship• Many-to-many relationship

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Establishing a One-to-Many Relationship

• Open Relationships window• Add tables• Establish

relationships

Show Table window

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Relationships Between Tables

Edit Relationshipsdialog box

One-to-many relationships

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Relationships WindowJoin lines

1 side

Many side:the “” (infinity symbol)

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Single-Table Queries• Show Table• Design Grid to

add– Field row– Table row– Sort row– Show row– Criteria Query Design Grid—Fields, Sorting, and Criteria

Query Design—Tables

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Datasheet View of Results

Query results inDatasheet view

Only accounts with abalance over $5,000

Nine records matchthe criteria

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Specifying Criteria for Different Data Types

• Field data type• Delimiters• Criteria

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Wildcards• The question mark (?)– Example: H?LL will return Hall, Hill,

and Hull• The asterisk (*)– Example: S*nd will return Sand, Stand,

and StoryLand

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Operators & Operands• Operators• Operands– Use >10 For a Price field, items with a price over $10.00.– Use >=10 for a Price field, items with a price of at least

$10.00.– Use <>10 for a Price field, items with a price not equal to

$10.00.– Use #2/2/2012# for a field with a Date/Time data type, such

as a ShippedDate field, orders shipped on February 2, 2012.– Use “Harry” for a text field, find the name Harry.– Use Date( ) for an OrderDate field, orders for today’s date.– Use Between #1/1/2012# and #3/31/2012# for a specified

interval between a start and end date, including the start and end dates.

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Null and Zero-Length Strings

• Null • Is Not Null

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Query Sort• Determines the order of records • Determined from left to right

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AND, OR, and NOT Criteria

• And operator• Or operator• Not operator

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Using the Query Wizard• Launch Query Wizard• Modify Query in Design view

Query Wizard

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Query Wizard

Select a Table or Query

Fields already moved to the Selected Fields list

Move a single field to the Selected Fields list

Move all fields to the Selected Fields list

Remove a single field from the Selected Fields list

Remove all fields from the Selected Fields list

Select detail or summary data

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Multi-Table Queries• Permit multiple tables• Use related tables• Similar to creating a single-table

query• Fixing a common problem

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Resources

Chapter 1 & 2Relational Databases and Queries

Exploring Microsoft Access 2010