1. Normalization Queries (contd)
LSP 121
Normalization
Queries (contd)

2. * Normalization
Normalization is the process of efficiently organizing your data
Normalizing your database can drastically improve its performance
This becomes especially important with very large databases
Normalization techniques include:
Avoiding data redundancy (ie avoid repetition of data)
Ensuring proper data dependencies
See example…

3. Normalization Let’s create a database for a car club
What if one person owns multiple cars? (One owner can have many cars, so this is 1:M relationship)
Table: Members: In this table, we would have to repeat all of the person’s info (MemberID, Name, Phone, etc, etc for EVERY car they own)
This is called data redundancy and is very BAD!
Instead, let’s create an additional separate table just for the cars. We’ll call this table Cars
We can still connect the car with its owner by including a field in the Cars table MemberID field from the Owners table
This is called establishing a “relationship” between the tables

4. * Data Redundancy A major no-no in database design.
Can lead to all kinds of problems down the road.
For example, suppose you had a database in which you store a person’s phone number in three different tables. Now, suppose you updated a member’s phone number in one table, but forgot to do it in another? This is a very common and can really mess things up.
You should try to limit fields to one place only.
However, you can “associate” fields between two tables.
Eg: In the ‘Cars’ table, you can refer to the MemberID from the ‘Members’ table.

5. Normalization Example
Car Club (original table)
Member ID (primary key)
Member Name
Member Address
Member City
Member State
Member Zip
Member Phone
Dues Paid?
National Member?
Model of Car
Make of Car
Year of Car
Note:
If a member has >1 car, the first 9
fields will be repeated multiple times
This is pointless – and dangerous!
MemberInfo
Member ID (primary key)
Name
Address
City
State
Zip
Phone
Dues Paid? National Member?
Relationship
Cars
Model of Car
Make of Car
Year of Car
Member ID (not
a primary key here!)
Primary Key in MemberInfo table
“Foreign Key” in Cars table?
1:M (“one-to-many”) relationship
Why isn’t MemberID a primary key in the CarTable table?

6. Data Redundancy Data Redundancy: A bad idea!
Key Point: Do every thing you can to avoid repeating data.
Database people do everythng they can to avoid data redundancy.
For example, each time you add a new car for a user, you should not have to repeat all of the user’s personal info (name, address, phone, etc, etc) all over again.
Instead, place the user’s personal info in one table (e.g. “Members”) and have a separate table for cars owned by the members of the club.
We then create a relationship between the two tables.

7. Another Normalization Example
Student ClassRecords
Student ID (primary key)
Name
Address
City
State
Zip
Phone
Major
Minor
Degree Sought
Class Name
Grade
Number Credits
The first 10 fields
are repeated for each course
Student Info
Student ID
Name
Address
City
State
Zip
Phone
Major
Minor
Degree Sought
Courses
Class Name
Grade
Number Credits
Student ID
After
StudentID is a primary key in the StudentInfo table and becomes a “foreign key” in the Courses table.
There is a 1:M (one-to-many) relationship between students and courses. That is, one student can have many courses.
Before

8. Practice Example Customer ID Customer Last Name Customer Phone
Imagine a table of your customers and all of your sales to them.
Would you change the design of your database?
If so, how many tables would you want in this case?
Primary keys? Foreign keys?
Customer ID
Customer Last Name
Customer Phone
Customer Address
Customer City
Customer State
Customer Zip
Sales Transaction Date
Sales Amount
Item
Clearance Item?

9. Practice Example Table: Customers CustomerID (primary key) LastName
Phone
Address
City
State
Zip
CustomerID
Customer Last Name
Customer Phone
Customer Address
Customer City
Customer State
Customer Zip
Sales Transaction Date
Sales Amount
Item
Clearance Item?
Table: Sales
InvoiceID (primary key)
CustomerID (foreign key)
SalesTransactionDate
SalesAmount
Item
ClearanceItem?

10. Relationships You can create a relationship between any tables by hand
Click Tools  Relationships
Add the two tables to the view, click on one of the fields (e.g. StudentID) drag it over to the other table’s identical field (StudentID) and un-click
Check Enforce Referential Integrity (you don’t want children records without parents) 10

11. Relationships
Access automatically creates a relationship between the two tables if:
you create two tables
the first table has a primary key
you carry that primary key over to the second table as a foreign key
the primary key and the foreign key are spelled the same and have the same type

12. Data 1 Smith 555-5555 Palos Heights 2 Chen 666-6666 LaGrange
3 Wilson Chicago
3/3/ Shirt N 1
3/3/ Scarf N 1
3/4/ Jeans Y 3
Important: Note the last column in the second table references the primary key (e.g. customerID) from the first table.
Let’s do the first part of today’s activity.

13. Simple Queries - contd
To create an Access query, don’t use the query wizard. Instead, create query in Design view
Let’s see how Access does it
Copy the Pets database from the Basic Information page to your desktop (or My Documents)
Then open the Pets database
If you don’t see any tables/queries etc on the left, click on the down-arrow and choose ‘All Access Objects’

14. * Query on Dates
You can query based on dates, but only if the data was stored as date/time
E.g. to search for dates after Jan , you would type: >1/1/2004
In a query, dates should be entered with # before and after the date. Note that dates can be in written many different formats, ie #1/1/2004#, #January 1, 2004#, #1-Jan-2004#
Access typically puts these in FOR you
Different databases have different ways of dealing with dates.

15. ** Queries – Using ‘OR’
In Access, put each criterion in a different row
If you put criteria in the same row, the query will work as an AND query (discussed next)
Customers with City=“Chicago” OR first name = “Jack”

16. Another way of using ‘OR’
If you are looking for different values within a single field (e.g. State), you can simply type the word ‘OR’ between each value:
E.g. You can look for records in the state of Indiana or Tennessee or Ohio by saying
“IL” OR “TN” OR “OH”
E.g. Show all pets that are birds or snakes:

17. ** Queries – Using ‘AND’
Logical AND - you can make multiple entries in the query boxes.
E.g. In the Type field enter “Dog” and in the Color field enter Brown
In Access, putting criteria in the same row is how you accomplish an AND effect
Recall that this is different from an OR query, where the different values must be on separate rows
E.g. Show all brown dogs:

18. ** Queries – Using ‘AND’
In Access, putting criteria in the SAME row is a way of accomplishing an AND effect
This example shows customers with city = “Chicago” AND first name = “Jack”

19. AND Queries contd Logical AND - You can also use an AND in one field.
For example, in the Size field you can enter
>=3 AND <=9
Possible operators include =, <>, <, >, <=, >=

20. Queries That Calculate
When performing a query, you can aggregate data together from a series of records
E.g. Find all customers born before 1970 and calculate their average sales.
You can do various basic statistical calculations such as: Count, Sum, Avg, Max, Min, Standard deviation, etc
Certain calculations can be performed only on certain datatypes.
E.g. You can not calculate the average of FirstName

21. Viewing Totals
To see these values, you need to click on Design  ‘Totals’
Totals can be found in the ‘Show/Hide’ box
You will now see an additional row called ‘Total’ in your query design view
Under Total, the ‘Group By’ criteria is important…

22. Example
Say you have a database for a vet that treats dogs. Each dog treated has an entry including ID, weight, and height
If you want to find the average weight and height of all pets
* IMPORTANT: Note that under ‘Total’, we set ‘Group By’ ‘Count’ for type (it will show how many pets there were) and to ‘Avg’ for weight (shows the average)

23. Example
What if you want to find the average height and weight for all dogs?

24. Example
What if you want to find the minimum and maximum weight for all dogs?
Note that you have to include the Weight field twice.

25. More Examples You can also perform totals on groups of records.
For example, suppose you want to count how many different types of pets the vet has on record
This example is not as intuitive as the others. For example, you would not know that the ‘Type’ field should not be grouped. Learning to skillfuly query a database takes some reading and practice.

26. Further Examples?
Experiment with more queries