Second Normal Form (2NF)

A table is said to be in its Second Normal Form if it satisfied the following conditions:-

1) It satisfies the condition for the First Normal Form (1NF),

2) It does not include any partial dependencies where a column is dependent only on a part of a primary key.
3) It should remove subsets of data that apply to multiple rows of a table and place them in separate tables.
4) It create relationships between these new tables and their predecessors through the use of foreign keys. 

For example suppose we have a table CustomerOrderDetail , which contains the customer details and its order details

Table Name:-CustomerOrderDetail

Primary Key :- CustomerId + OrderId

CustomerId	OrderId	CustomerName	OrderName	Price
1	1	Lily	Laptop	35000
2	2	Salony	Mouse	150

In this table, the primary key is composition of two columns CustomerId + OrderId. Now this table is in 1NF but it is not in the 2NF since the column CustomerName is dependent on the column CustomerId and the column OrderName is dependent on the column OrderId which violates the second condition for the 2NF.

We can break this table into three different tables to convert it into the 2NF. These tables are given below:-

Table name:- Customer

Primary Key: - CustomerId

CustomerId	CustomerName
1	Lily
2	Salony

Table name:- Order

Primary Key: - OrderId

ProjectId	ProjectName
1	Laptop
2	Mouse

Table name:- CustomerOrderDetails

Primary Key: - CustomerId + OrderId

CustomerId	OrderId	Price
1	1	35000
2	2	150

Now all the three tables are in 1NF and all the columns of these tables are fully depended on their respective primary keys.