Fifth Normal Form

Sanjana Yadav
Last Updated: May 13, 2022


The normalization process involves removing duplication from a connection or group of relations. Anomalies in insertion, deletion, and update can be caused by relation redundancy. As a result, it aids in reducing relational redundancy. 

Normal forms are used in database tables to remove or decrease redundancy.

Before studying the fifth normal form, it is recommended that you master the first, second, third, BCNF, and fourth normal forms.

Fifth Normal Form(5NF)

A Relation is considered to be in 5NF, if and only if -

  • It's in the 4NF.
  • If we can further break down the table to remove redundancy and anomaly and then re-join the decomposed tables using candidate keys, we should not lose the original data or create a new recordset. In other words, combining two or more deconstructed tables should not result in the loss of records or the creation of new records.

5NF is also called the Project-join normal form (PJ/NF).


Let us consider that class 12 has Physics, Chemistry, and Mathematics as its subjects and class 11 has only Mathematics this year.

In the above table, Sam takes both Physics and Mathematics classes for class 12 but does not take Mathematics for class 11. In this scenario, a combination of all of these variables is needed to identify the valid data.

Assume that we add a new Class as Class 10 but don't know what the subjects will be or who will be taking them; therefore, we leave Teacher and Subject as NULL. However, because all three columns act as a primary key, we cannot leave the other two columns blank.

As a result, we must deconstruct the table in such a way that it meets all of the criteria up to 4NF, and when we connect them using keys, we should get the correct record. We can better portray each teacher's subject area and classes here. We may divide the above table into three parts: T1( SUBJECT, TEACHER), T2(CLASS, TEACHER), and T3(CLASS, SUBJECT).

Record T1:

Record T2:

Record T3:

Each combination is now in three different tables. If we want to know who is teaching which subject in which class, we may join the keys of each table and get the answer.

For example, to determine who teaches Mathematics to Class 12, we would choose Mathematics and class 12 from table T3 above, then connect with table T1 using Subject and filter out the Teacher names. Then, combine with table T2 using Teacher to get the proper Teacher name. 

To retrieve the relevant data, we linked important columns from each table. As a result, there is no loss or additional data, meeting the 5NF condition.


SELECT t3.Class, t3.Subject, t1.Teacher
where t3.Class = 'Class 12' and t3.Subject= 'Mathematics'
AND t3.Subject = t1.Subject
AND t3.Class = t2.Class
AND t1.Teacher = t2.Teacher;



  1. What is a normal form in DBMS?
    Removing redundancy from a relation or set of relations is known as normalization. Redundancy in relation may result in insertion, deletion, and update anomalies. As a result, it aids in reducing relational redundancy. Normal forms are used in database tables to remove or decrease duplication.
  2. How do you find the normal form?
    Steps for determining the highest normal form of a relationship: Find all of the relation's possible candidate keys. Separate all attributes into two groups: prime attributes and non-prime attributes. Check for the first normal form, then the second, and so on.
  3. What is the first normal form in DBMS?
    In a relational database, the first normal form (1NF) is a property of a relation. If and only if no attribute domain has relations as elements, a relation is in first normal form. SQL does not permit the creation or use of table-valued columns, hence most relational databases must be in first normal form.
  4. What is 2nd normal form in DBMS?
    The second normal form (2NF) is a kind of normal form employed in database normalization. A relationship is in the second normal form if it meets the following two conditions: Its initial normal form. It lacks any non-prime property functionally reliant on any suitable subset of any relation's candidate key.
  5. How do you find the third normal form?
    A relation that is in the First and Second Normal Form and has no non-primary-key attributes that are transitively reliant on the primary key is in the Third Normal Form (3NF). Note: If A->B and B->C are both FDs, then A->C is referred to as transitive dependence.

Key Takeaways

  • Cheers if you reached here! In this blog, we learned the basics of the Fifth Normal Form.
  • Is it all about Normalization? No, there's a lot more to it than that. 
  • We attempted to cover all of the fundamentals of the Fifth Normal Form and an example to understand them better.
  • Hopefully, after reading the above information, you will be able to connect to the same and try to implement it in real-life scenarios.

On the other hand, learning never ceases, and there is always more to learn. So, keep learning and keep growing, ninjas!

Check out the Top 100 SQL Problems to get hands-on experience with frequently asked interview questions and land your dream job.

Good luck with your preparation!


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