Hello Readers,

Today I am writing about an important type of database, Relational Databases.

Relational Database is a type of database. The data is organized in the form of relations i.e. Tables. A table contain the attributes and tuples . In simple words, attributes are columns and tuples are rows. The attributes define qualities about an entity. A tuple contains value for a particular attribute of an entity.

Lets take an example.

PERSON

Here is relation named Person. The attributes of this relation are : Person_ID , Name, Age, Place. There are three tuples inserted into the Person relation.

Primary Key

A primary key is an attribute that uniquely identifies tuples in a relation.

Here PERSON_ID is taken as primary key in the person relation , it uniquely identifies each person (each tuple) .

• Primary key should be unique . It should not be repeated in any tuple.

• Primary key cannot contain NULL values. It must contain data.

• A table can have only one primary key.

Alternate Keys

The attributes that uniquely identify tuples of a relation , but cannot be qualified as a primary key are the alternate keys.(In the above example , Name can be alternate key as the names are unique)

Foreign Key

The attributes of a relation that reference the attributes of another relation are the foreign keys.

In the example above Person_ID is the foreign key. It references the primary key of person table (person_id of person table).

• The table that references other table is the derived table . The table that is being referenced is the base table.

• Foreign key attribute in the derived table should contain only the values that are in the attribute of the base table.

• Foreign key need not be unique ( In the derived table , the foreign key values can also be repeated )

• There can be any number of foreign keys in derived table.

This is all about the basics of the Relational Databases.

Thank You for reading.