Second Normal Form (2NF)

DBMSDatabaseMySQL

What is 2NF?

The second step in Normalization is 2NF.

A table is in 2NF, only if a relation is in 1NF and meet all the rules, and every non-key attribute is fully dependent on primary key.

The Second Normal Form eliminates partial dependencies on primary keys.

Let us see an example −

Example (Table violates 2NF)

<StudentProject>

StudentID

ProjectID

StudentName

ProjectName
S89
P09
Olivia
Geo Location
S76
P07
Jacob
Cluster Exploration
S56
P03
Ava
IoT Devices
S92
P05
Alexandra
Cloud Deployment


In the above table, we have partial dependency; let us see how −

The prime key attributes are StudentID and ProjectID.

As stated, the non-prime attributes i.e. StudentName and ProjectName should be functionally dependent on part of a candidate key, to be Partial Dependent.

The StudentName can be determined by StudentID, which makes the relation Partial Dependent.

The ProjectName can be determined by ProjectID, which makes the relation Partial Dependent.

Therefore, the <StudentProject> relation violates the 2NF in Normalization and is considered a bad database design.

Example (Table converted to 2NF)

To remove Partial Dependency and violation on 2NF, decompose the above tables −

<StudentInfo>

StudentID
ProjectID
StudentName
S89
P09
Olivia
S76
P07
Jacob
S56
P03
Ava
S92
P05
Alexandra


<ProjectInfo>

ProjectID
ProjectName
P09
Geo Location
P07
Cluster Exploration
P03
IoT Devices
P05
Cloud Deployment


Now the relation is in 2nd Normal form of Database Normalization

raja
Updated on 15-Jun-2020 13:03:23

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