Keys use in Database

Define Relational Keys

i) Primary key

A primary key is field or group of field that is used to identify each record uniquely in a file. It is also known as key field. The data in key field is unique for each record. For example, student ID field identifies each student uniquely because no two students can have the same ID.

ii) Composite Primary key.

The primary key that consists of more than one attribute is called composite primary key.

iii) Foreign key

A foreign key is a field or combination of fields in a table that reference a primary key in another relation. The key connects to another table when a relationship is being established between two tables. A table may contain many foreign keys.