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Primary Key
Primary key is a field which is used to uniquely identify records in a database. It is a unique field

and it cannot be left blank. There can be only one primary key in a table.
In the Student Table, Student_ID is the primary key, which is used to uniquely identify the records.

Foreign Key

A foreign key is a field in one table that refers to the primary key in another table. It helps to
establish a relationship between two tables. A foreign key makes sure that data in one table
matches data in another table.

Let’s understand the relationship among tables in a relational database with the help of an example.
Student Table

Student_ First_ Last_ Date of Email Course_
ID Name Name Birth ID

1 Aarav Sharma 15-Mar-2012 aarav.sharma@gmail.com C101
2 Priya Patel 20-May-2012 priya.patel@gmail.com C102
3 Rahul Verma 10-Mar-2012 rahul.verma@gmail.com C103
4 Sneha Iyer 25-Nov-2011 sneha.iyer@gmail.com C101

5 Dev Kapoor 12-Jul-2012 dev.kapoor@gmail.com C102

Course Table

Course_ID Course Name Teacher_Name

C101 Mathematics Dr. Ramesh Kumar

C102 Science Ms. Priya Sethi
C103 Social Studies Mr. Rahul Sharma

In this example, the Student Table and Course Table share a common field named Course_ID.
The Course_ID in the Student Table is a foreign key that references the Course_ID (a primary key)
in the Course Table.

From this relationship, the following information gets extracted:

One Course (Course Table) is opted by many Students (Student Table).
Each student (Student Table) is linked to only one course via Course_ID (Foreign Key).

Tick ( ) if you know this.

▶ Data backup in databases means making a copy of the database files.
▶ A record is a collection of related data stored in different fields.

MySQL: My First Database 59