1. INFO/CSE 100, Spring 2005 Fluency in Information Technology
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INFO/CSE 100, Spring 2005
Fluency in Information Technology
11/12/2018
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2. Readings and References
Fluency with Information Technology
Chapter 14, Database Queries
References
Access Database: Design and Programming
by Steve Roman, published by O'Reilly
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3. entity-relationship diagram for Library database
Price
Name
ISBN
Title ID
Phone ∞
WrittenBy ∞
Books
Authors ∞
PublisherOf 1
Publishers
entity-relationship diagram for Library database
Books, Publishers, Authors are tables
Price, ISBN, Title are attributes of the table Books
There is a relationship between Books and Publishers
1 Publisher can have many Books ID
Phone
Name

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Create a new database
We are going to be using MS Access.
Its available on the Lab machines and in MS Office if you have that installed on your home computer already.
Step 1: create a new database , with a .mdb file extension
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5. Create a new table in the database
MS Access tries to be friendly and offer you some choices!
Select "Create table in Design View".
Do not use the Wizard!
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6. Creating a table in Design view
Aha! Now you've got to enter in the attributes {fields} of the table.
Attributes have a field name, data type, and a description.
In this example, three fields are being created: ISBN, Title, and Price.
ISBN field is specified as the key (see key icon). Remember that the key field must be unique!
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Entering Table Data
Once the table has been added you must view leave the Design View to enter data into the table.
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Build another table
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9. Add publisher ID to books
Field properties allow you to add more details about each attribute {field}, including things
like size, format (for dates), number of decimal places, required, etc…
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10. Create the link between the tables
From the Relationships view. We can create a link by dragging a line between
a field from one table to a field on another table.
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11. Hey presto, we have a database!
Price
Name
ISBN
Title ID
Phone ∞
WrittenBy ∞
Books
Authors ∞
PublisherOf 1
Publishers
Hey presto, we have a database! ID
Phone
Name

12. Two tables with a relationship
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Create a query
Create a query in Design View.
Step 1: select query from the object lists.
Step 2: select the tables you want to query from.
Step 3: select the fields you want to query from.
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14. The query produces a new (virtual) table
A query produces a new table, of which we see the results.
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15. Project (select particular columns)
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16. Select particular rows
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SQL behind the scenes
Books.ISBN == books table and ISBN field
Books.* all fields from the books table!!
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18. Recall: Structure of the database
A database contains one or more tables
Tables include entities with attributes
There are relationships defined between the entities in the various tables
Retrieve information from the tables using queries
We designed and partially implemented a simple library database in the previous lecture
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19. Books Authors Publishers Price Name ISBN Title ID Phone ∞ WrittenBy ∞
PublisherOf 1
Publishers ID
Phone
Name

20. What is the relationship?
This relationship is 1-to-many:
One publisher is responsible for many books.
Each book has only one publisher.
Books ∞
PublisherOf
The two tables are joined using the publisher ID number.
The publisher ID is the primary key for each entry in the publishers table.
Therefore, each publisher must have a unique publisher ID.
The publisher ID is a foreign key for each entry in the books table and we have requested referential integrity
Therefore, the given publisher ID must exist in the publishers table. 1
Publishers
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21. Referential Integrity
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22. PubID must reference an actual publisher
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23. What is the relationship?
Price
Name
ISBN
Title ID
Phone ∞
WrittenBy ∞
Books
Authors
This relationship is many-to-many:
One book may have several authors.
One author may have written several books.
We need a unique identifier for each book.
We already selected the ISBN as the primary key and asked Access to make sure that there are no duplicates
We need a unique identifier for each author
We will define an author table with a unique ID for each author
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authors table
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25. Link one book with many authors?
We DO want:
to link each book to one or more authors
We DON'T want
to specify extra fields (author1, author2, author3,…)
this is wasteful and limits the max number of authors
to specify each book entry several times, naming a different author in each row
this duplicates all the other information about the book
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26. Add a cross-reference table!
Refine the design so that it includes another table that is a book-author cross reference
Each entity in the table is a single cross reference
Attribute: ISBN
Attribute: Author ID
No primary key
Now we can break the many-to-many relationship into two 1-to-many relationships that we already know how to implement
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27. Define new cross-reference entities
Price
Name
ISBN
Title ID
Phone 1 ∞ ∞ 1
Books
Book/Author
Authors
ISBN
AuthorID
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book-author table
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29. Define the new relationships
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30. Define a query that uses the relationship
Query By Example
actual SQL

31. Get the new view of the data
Notice that this view has redundant data
That's okay, because we are not storing it this way, just presenting it
The redundant items (Alex, Another Press) came from a single entry in a table – they are guaranteed to be identical
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32. Now we've implemented this entire schema.
Price
Name
ISBN
Title ID
Phone ∞
WrittenBy ∞
Books
Authors ∞
PublisherOf 1
Now we've implemented this entire schema.
Publishers ID
Phone
Name

33. View: All Books from “Another Press”

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View: All Books by Alex
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35. View: All info about a given ISBN