A table is the primary unit of physical storage for data in a database. A key attribute or set of attributes uniquely identifies an entity instance. There are different types of keys including super keys, candidate keys, primary keys, foreign keys, and simple or composite keys. A simple key consists of a single attribute while a composite key consists of more than one attribute. The primary key uniquely identifies records in a table and cannot contain null values. A foreign key in one table references the primary key in another table and is used to define relationships between tables.

1. “Data Base “
Name: Sana Salim
Dept: IT
M.Cs 3rd
Topic: Relational Keys

2. “Table”
• “A table is the primary unit of physical storage
for data in a database.”
• Usually a database contains more than one
table.

3. “Key Attributes”
• An attribute or set of attributes to identify an
entity instance uniquely
• Types:
– Super key
– Candidate key
– Primary key
– Foreign Key
– Simple or Composite Key

4. “Example of Key”
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4
S1038 Shoaib Baber Model Town BCS 3
S1015 Tahira Ejaz Wah Cantt MCS 2
S1018 Arif Mehmood Satellite Town BIT 4
S1025 Suhail Shah Garhi Shahoo BCS 6

5. “Simple or Composite Key”
• A key consisting of single attribute is called simple key, e.g.,
StudID, itemNo
• A key consisting of more than one attribute is known as
composite key, like {Program_Code, Course_Code}

6. ProgCode CourseCode MarksAlloc CrHrs
MCS DS 100 3
MCS DBS 100 3
MBA DBS 100 3
BCS NW 100 3
OFFERING
“Example”

7. “Primary Key”
• Primary key is a unique identifier of records in
a table.
• None of its attributes can have NULL values
• Primary key values may be generated manually
or automatically.
• A primary key can consist of more than one
field.

8. “Foreign Key”
foreign key field
primary key field parent table
Directors
Movies
child tablerelationship

9. “Relationship Types”
• One-to-one
• One-to-many
• Many-to-many

10. “Super Key”
• Any set of attributes containing a super key is also a super
key since it too uniquely identifies an entity e.g. {StudID,
major}
• For example, for EMPLOYEE and STUDENT entity types
EmpID and StudID are the superkeys respectively.

11. “Example”
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4
S1038 Shoaib Baber Model Town BCS 3
S1015 Tahira Ejaz Wah Cantt MCS 2
S1018 Arif Mehmood Satellite Town BIT 4
S1025 Suhail Shah Garhi Shahoo BCS 6

12. “Candidate Key”
• A candidate key is the super key that does not
contain extra attributes.
• It might have more than one attribute that uniquely
identifies an entity. e.g {name, address}

13. “Example”
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4
S1038 Shoaib Baber Model Town BCS 3
S1015 Tahira Ejaz Wah Cantt MCS 2
S1018 Arif Mehmood Satellite Town BIT 4
S1025 Suhail Shah Garhi Shahoo BCS 6

14. Thank you!