2 Normal Form

The Second Normal Form (2NF) is a concept in database normalization that builds upon the First Normal Form (1NF). It addresses issues related to partial dependencies in a relational database. To be in 2NF, a table must satisfy the following conditions:

1. It must already be in 1NF, which means that it contains only atomic values (no repeating groups or arrays in columns).

2. It should not have partial dependencies, which occur when non-key attributes (attributes not part of the primary key) depend on only part of a candidate key.

In simpler terms, 2NF eliminates redundancy and ensures that all non-key attributes are functionally dependent on the entire primary key, not just part of it.

Here's an example to illustrate 2NF:

Consider a table called Orders with the following attributes:

OrderID	ProductID	ProductName	CustomerID	CustomerName	Quantity
1	101	Laptop	1001	Alice	2
2	102	Smartphone	1002	Bob	3
3	101	Laptop	1003	Carol	1

In this table:

• OrderID is the primary key.

• ProductID is part of the candidate key because it identifies a product within an order.

• CustomerID is also part of the candidate key because it identifies a customer associated with an order.

• ProductName is functionally dependent on ProductID.

• CustomerName is functionally dependent on CustomerID.

• Quantity is functionally dependent on both OrderID and ProductID because it represents the quantity of a specific product in a specific order.

However, there's a problem related to partial dependency. The Quantity attribute depends on ProductID, which is only part of the candidate key. This violates the 2NF because non-key attributes should depend on the entire candidate key.

To bring this table into 2NF, you should split it into two separate tables: one for orders and another for order details. Here's how it might look in 2NF:

Table: Orders

OrderID	CustomerID
1	1001
2	1002
3	1003

Table: OrderDetails

OrderID	ProductID	Quantity
1	101	2
2	102	3
3	101	1

In this revised structure, each table adheres to 2NF. The Quantity attribute now depends on the entire primary key (composite key of OrderID and ProductID). This eliminates partial dependencies and reduces data redundancy, making the database more efficient and easier to manage.