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Transcript of 1 Chapter 1 & 2 Relational Databases and Queries CS101 WVU.
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Chapter 1 & 2Relational Databases and Queries
CS101 WVU
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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
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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
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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 Views
Datasheet 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