Concepts of Database Management Seventh Edition Chapter 4 Keys and Relationship.

Concepts of Database ManagementSeventh Edition

Chapter 4

Keys and Relationship

Objectives

• Understand different type of keys in a Table.

• Understand the different type of Table relationship

• Identify the primary key and foreign key to create a relationship.

• Create primary and foreign key in an actual DBMS

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Table Relationship

• Remember in Chapter 1 we discuss the hierarchy of data, namely:– Field or Column– Record or Row– Table or File– Database

• Now, Tables normally does not stand alone, that is, in the modern database software like MS Access, mySQL, Oracle or MS SQL, table(s) normally has relationship with another table.

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Three Types of Relationship

• There are three types of table relationship:– One to one or denoted as 1:1– One to many or denoted as 1:M– Many to Many or denoted as M:N

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Examples of One-to-One Relationship

• A student belongs to only one Program

• A student has one and only ID

• An employee has one computer assign

• Could you name your own example?

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Examples of One-to-Many Relationship

• A Division could have more than one Program offered

• A Program could have many students enrolled

• Could you name your own example?

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Examples of Many-to-Many Relationship

• A student could take many course and a course could have many students

• An author could have many books and a book could have many author

• A music album could have many artists/performers and an artist/performer could have many albums

• Could you name your own example?

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Key in a table

• A key in a table is a field or group of fields that creates identity, makes relationship with another table and/or make a table more efficient.

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Primary Key & Foreign

• A Primary key is a key that uniquely identifies a row in each table. It is normally denoted with its first two letters, namely, PK.

• A Foreign key is a key borrowed from another related table (that’s why its foreign) in order to make the relationship between two tables. It is normally denoted with its first two letters, namely, FK.

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Examples from Premier Database – Primary Key

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Repnum uniquely identifies the Rep table and is the primary key of this table.

Examples from Premier Database – Primary Key

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Customernum uniquely identifies the Customer table and is the primary key of this table.

Examples from Premier Database – Primary Key

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Ordernum and Partnum makes up the primary keyOf the OrderLine table. This is what is known as a CompositePrimary key, that is, primary key that is made up of more thanone field.

Examples from Premier Database

• Could you identify any more primary keys from Premier Database?

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Examples from Premier Database – Foreign Key

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Repnum is a Foreign key borrowed from Rep table

Examples from Premier Database

• Could you identify any more foreign keys from Premier Database?

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Notation example

• One Rep could have one or more customer (one to many) using

Primary and foreign key to create the relationship.

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Customer

Customernum (PK)CustomernameStreetCityStateZipBalanceCreditLimitRepnum (FK)

Rep

Repnum (PK)LastnameFirstnameStreetCityStateZipCommissionRate

1

M

Notation example

• Always remember the many side has the Foreign key. In this case the many side is on the Customer table and therefore has the foreign key Repnum which is the primary key of Rep table.

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Customer

Customernum (PK)CustomernameStreetCityStateZipBalanceCreditLimitRepnum (FK)

Rep

Repnum (PK)LastnameFirstnameStreetCityStateZipCommissionRate

1

M

Examples from Premier Database

• Could you identify the different relationship among tables in Premier Database because of the Primary and Foreign keys?

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Referential Integrity

• Referential Integrity means that the Foreign key must match in terms of actual values and data types with the related Primary Key.

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Referential Integrity

• Example:

• The foreign key RepNum in Customer must match with the primary key RepNum in Rep table.

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Referential Integrity

• In terms of Data Type

• Customer RepNum (Foreign Key) has Text Data type and Rep RepNum (Primary Key) has also Text Data type.

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Seatwork

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• Alexamara and Henry Books• Identify the primary key and foreign keys for each table. Put

the name of the table and name its primary key and if there is a foreign key identify the foreign key.

• Identify how each table that has the foreign key relates to another table. See slide No. 16 and 17

Demo in creating Primary and Foreign Key in MS Access

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Referential Integrity

• In terms of actual Values

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Non-Graded Seatwork

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• Alexamara and Henry Books

– Check the tables that are related to each other and then check data types for both Foreign and Primary Keys that are related.

– Check also the values of the related Primary Keys if you could find it in the related Foreign keys.

– Try to enter values in the Foreign Key that could not be found in related table that has the Primary Key. Did MS Access pops out an error message? What does it say?

On-your-own Exercise

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– Imagine we want to make a simple appointment database for a small clinic here in Pohnpei with a fictitious name Health Wealth clinic. And the database would record appointments for Patients with their Doctor on a given date.

– Now a Patient could have one or more appointments in Health Wealth clinic to one or more Doctor. – A Doctor could also have one or more appointment with one or more patients every day.– Create three tables, namely, Patients, Doctors and Appointments.– Create necessary fields for each table that you think should be there.– Create a Primary Key for each tables.– And create also Foreign keys if necessary to create relationship among tables.– Use the Database Tools to create the Relationship among tables after you created both the Primary Keys and Foreign

Keys.– Show your work to me after you are done.

Summary (continued)• Modern database normally has tables that has

logical relationships with one another.

• Three primary type of relationships are one-to-one, one-to-many and many-to-many.

• Each row/record in a Table should be unique using a Primary Key

• To create a relationship among tables you must have the Foreign key on the other table.

• Referential Integrity protects the integrity of your data by matching both your Primary key and Foreign in terms of Data types and actual values.

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