1. Introduction to Relational Database Introducing PRIMARY KEY
Thaddeus Konar
LCC CIT Instructor
T. Konar

2. Introduction to Relational Database
Summary of what we already know:
Database allows storage of related data in the tables as a collection of relations.
Each relationship is represented in a table.
Database stores data in multiple two-dimensional (rows and columns) tables. Each table defines a relationship.
Access uses some non-standard Database nomenclature:
Each column represents a field and the real technical term for it is ATTRIBUTE.
Each row represents a record and the real technical term for it is ENTITY.
There is also a relationship between tables (single value in one table can point to a row of data in another table).
T. Konar

3. Introduction to Relational Database
Here is my library card:
Classification
Name
Primary Key College Library
Thaddeus Konar Instructor CIT
DOB: 07/04/1776 ISSUED: 09/01/2003
1295
Department
My library card has many fields to hold the relevant information about me.
Day of Birth
Issue Date
ID Number
T. Konar

4. Introduction to Relational Database
My library card contains Related Data (relates to me – a library patron)
Primary Key College Library
Thaddeus Konar Instructor CIT
DOB: 07/04/1776 ISSUED: 09/01/2003
1295
Every field contains the information describing me. There is no guarantee that there is no another Thaddeus Konar, or another 200+ old person, but there should only be one library patron with ID # 1295
T. Konar

5. Introduction to Relational Database
Primary Key College Library
John Vanko Student
DOB: 11/12/1976 ISSUED: 09/01/2003
7645
Primary Key College Library
Stephen Packo Instructor ENG
DOB: 05/14/1973 ISSUED: 02/15/2003
2365
Primary Key College Library
Stephen Packo Instructor ENG
DOB: 05/14/1973 ISSUED: 02/15/2003
2365
Primary Key College Library
Debbie Smith Student
DOB: 09/23/1982 ISSUED: 09/01/2003
2345
Primary Key College Library
Stephen Packo Instructor ENG
DOB: 05/14/1973 ISSUED: 02/15/2003
2365
Primary Key College Library
Stephen Packo Instructor ENG
DOB: 05/14/1973 ISSUED: 02/15/2003
2365
Primary Key College Library
Thaddeus Konar Instructor CIT
DOB: 07/04/1776 ISSUED: 09/01/2003
1295
Primary Key College Library
Stephen Packo Instructor ENG
DOB: 05/14/1973 ISSUED: 02/15/2003
2365
Primary Key College Library
Mary Zaba Staff Adm
DOB: 02/03/1973 ISSUED: 02/01/2003
1256
Primary Key College Library
Karen Pstrag Staff Adm
DOB: 02/21/1964 ISSUED: 02/01/2003
2945
Other folks have their cards with information related to them.
T. Konar

6. Related data could be presented in a table as a record.
Introduction to Relational Database
Related data could be presented in a table as a record.
Each row represents a single RECORD (entity)
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date …
...
We have our ID cards, but the library would have the same information in one place. Hopefully use database and store this information in a table, one row per patron.
1295
Thaddeus Konar
1295
CIT
T. Konar

7. Introduction to Relational Database
Columns are table’s FIELDS (attributes) and they define the table format.
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT …
...
As you noticed, all cards have the same format and the same fields. ID number, Name, Classification, Dept, etc
T. Konar

8. Introduction to Relational Database
Every table has one FIELD (attribute/column) that uniquely identifies each RECORD (entity/row).
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT …
...
The attributes as my name, birth date, or job...do not identify me uniquely. The only attribute which does it is the ID Number
T. Konar

9. Introduction to Relational Database
The FIELD (attribute/column) that is unique for each and every RECORD (entity/row) in the table is designated as a PRIMARY KEY.
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT …
...
The same is for other library patrons. Only ID Number guarantees the unique identification of a single record.
T. Konar

10. Introduction to Relational Database
PRIMARY KEY identifies a single and unique RECORD (row) of the table. For this table there could be a duplicate Name, Classification, DOB, etc. but not ID Number.
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT …
...
Pretty much repeats what was said before.
T. Konar

11. Introduction to Relational Database
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT
2345
Debie Smith
Student
7645
John Vanko
2945
Karen Pstrag
Staff
ADM
1256
Mary Zaba …
2365
Stephen Packo
ENG
ID Number
Name
Classification
Dept.
Day of Birth
Issue Date
1295
Thaddeus Konar
Instructor
CIT
2345
Debie Smith
Student
7645
John Vanko
2945
Karen Pstrag
Staff
ADM
1256
Mary Zaba …
2365
Stephen Packo
ENG
So we have our library patrons table!
From the database point of view, this table has problems. The classification field values are repeated. This is not an efficient use of database. Also the ID number 1295 identifies me, my name, birthday, etc. But the department is really not part of me.
Data is duplicated
Data not ‘really’ pertaining to me (I am part of CIT, but CIT is not part of me)
T. Konar

12. Introduction to Relational Database
Patrons
ID_Number
Name
CID
DID
Day of Birth
Issue Date
1295
Thaddeus Konar 1
2345
Debie Smith 2
7645
John Vanko
2945
Karen Pstrag 3
1256
Mary Zaba
2365
Stephen Packo
Classification
Foreign Key
Points to the Primary Key in Classification
Table
Foreign Key
Points to the Primary Key in Department
Table
Department
ID_num
Description 1
Instructor 2
Student 3
Staff 4 …
The proper approach would be to split the data into three tables. We should add the Classification and the Department table. We designate the field CID in Patrons table as a pointer field to the Classification table, and DID in Patrons as a pointer field to the Department table. This pointer is called ‘Foreign Key’.
ID_num
Description 1
CIT 2
ENG 3
ADM 4 …
T. Konar

13. Introduction to Relational Database
Patrons
ID Number
Name
CID
DID
Day of Birth
Issue Date
1295
Thaddeus Konar 1
2345
Debie Smith 2
7645
John Vanko
2945
Karen Pstrag 3
1256
Mary Zaba
2365
Stephen Packo
Classification
Department
ID_num
Description 1
Instructor 2
Student 3
Staff 4 …
ID_num
Description 1
CIT 2
ENG 3
ADM 4 …
Each table must have a primary key, and our new tables will also have them.
Primary Key for Library Patrons Table
Primary Key for Classification Table
Primary Key for Department Table
T. Konar

14. Introduction to Relational Database
Patrons
CREATE TABLE classification ( id_num INT PRIMARY KEY, description CHAR(12), ); CREATE TABLE department ( id_num INT PRIMARY KEY, description CHAR(10), );
ID Number
Name
CID
DID
Day of Birth
Issue Date
1295
Thaddeus Konar 1
2345
Debie Smith 2
7645
John Vanko
2945
Karen Pstrag 3
1256
Mary Zaba
2365
Stephen Packo
Classification
Department
ID_num
Description 1
Instructor 2
Student 3
Staff 4 …
ID_num
Description 1
Instructor 2
Student 3
Staff 4 …
CREATE TABLE patrons ( id_number INT PRIMARY KEY, name CHAR(50), FOREIGN KEY cid REFERENCES classification (id_num), FOREIGN KEY did REFERENCES department (id_num), dob INT, issue_d INT );
You might ask, “How do you do that? How do you make one field point to another row in another table?” This is done by a programmer (database designer) and the code to create table like Patrons would look like this{}
You see that ID_Number field is declared to be Primary Key, and CID and DID are Foreign Keys pointing at other tables.{}
Also you will notice that two new tables are also declared with primary keys.
ID_num
Description 1
CIT 2
ENG 3
ADM 4 …
ID_num
Description 1
CIT 2
ENG 3
ADM 4 …
T. Konar

15. Introduction to Relational Database
Summary:
PRIMARY KEY is a unique field that identifies a single RECORD (row/entity) of the table.
PRIMARY KEY is a ‘target’ (lookup identifier) for a Foreign Key in other tables.
PRIMARY KEY of the relation is a unique identifier for that relation
Please remember that each record describes a single instance of a relation, and the table describes the structure of all relations in that table. Without Primary Keys we would not be able to identify a single record and it would not be possible to have the relations between different tables.
PRIMARY KEY can be one or more attributes, must be unique, must have a ‘fixed’ value, and can be created automatically.
T. Konar

16. Introduction to Relational Database
What is wrong with this table?
Cust. ID
Name
Phone 42
Bubba Smith 45
Debie Smith
John Smith 48
Karen Smith 56
Mary Smith 65
John and Karen have same phone number. That is OK.
There are two Mary Smith. That is OK
There are two people sharing the same ID. That is NOT OK!
T. Konar

17. Introduction to Relational Database
What is wrong with this table?
CID
Classification 1
Instructor 2
Student 3
Staff
Student and Instructor classification share the same ID. That is NOT OK!
T. Konar

18. Introduction to Relational Database
PRIMARY KEY Explained
The End
T. Konar