Advanced Database Management System - Tutorials and Notes: Normalization - solved exercises - Normal forms 1

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## Set of solved exercises in Normalization / Normalization Solved Examples / How to find candidate keys, and primary keys in database? / Sets of examples to find the keys of a tables / Process of Key finding in a database - Examples / Normalization to 1NF, 2NF, 3NF

Let us assume a table User_Personal as given below;

 UserID U_email Fname Lname City State Zip MA12 Mani@ymail.com MANISH JAIN BILASPUR CHATISGARH 458991 PO45 Pooja.g@gmail.co POOJA MAGG KACCH GUJRAT 832212 LA33 Lavle98@jj.com LAVLEEN DHALLA RAIPUR CHATISGARH 853578 CH99 Cheki9j@ih.com CHIMAL BEDI TRICHY TAMIL NADU 632011 DA74 Danu58@g.com DANY JAMES TRICHY TAMIL NADU 645018
• Is this table in First Normal Form?
Yes. All the attributes contain only atomic values.

• Is this table in Second Normal Form?
To verify this property, we need to find all the functional dependencies which are holding in User_Personal table, and have to identify a Primary key.
Let us do that by using the sample data. This leads to the following set of FDs;
F = { UserID U_email Fname Lname City State Zip,
Zip City State }
As UserID attribute can uniquely determine all the other attributes, we can have UserID as the Primary key for User_Personal table.
The next step is to check for the 2NF properties;
Property 1 – The table should be in 1NF.
Property 2 – There should not be any partial key dependencies.

Our table is in 1NF, hence property 1 is holding.
Primary key of our table is UserID and UserID is single simple attribute. As the key is not composite, there is no chance for partial key dependency to hold. Hence property 2 is also holding.
User_Personal table is in 2NF.

• Is User_Personal in 3NF?
To verify this we need to check the 3NF properties;
Property 1 – Table should be in 2NF.
Property 2 – There should not be any Transitive Dependencies in the table.

Table User_Personal is in 2NF, hence property 1 is satisfied.

User_Personal table holds the following Transitive dependency;

UserID Zip, Zip City State

Hence, property 2 is not satisfied and the table is not in 3NF.

Solution:
Decompose User_Personal. For this, we can use the functional dependencies Zip City State and UserID U_email Fname Lname City State Zip.

As a result, we can have the following tables (primary keys are underlined);

User_Personal (UserID, U_email, Fname, Lname, Zip)
City (Zip, City, State)

 UserID U_email Fname Lname Zip MA12 Mani@ymail.com MANISH JAIN 458991 PO45 Pooja.g@gmail.co POOJA MAGG 832212 LA33 Lavle98@jj.com LAVLEEN DHALLA 853578 CH99 Cheki9j@ih.com CHIMAL BEDI 632011 DA74 Danu58@g.com DANY JAMES 645018
Table - User_Personal

 Zip City State 458991 BILASPUR CHATISGARH 832212 KACCH GUJRAT 853578 RAIPUR CHATISGARH 632011 TRICHY TAMIL NADU 645018 TRICHY TAMIL NADU
Table – City

Both tables are in 3NF.
Hence, tables are normalized to Third Normal Form.

**********

2nf normalized

1. This is the best and most effective tutorial I have ever read so far in computer science field. I read a lot of tutorials and watched a lot of videos but got more and more confused. But now it is plain and crystal clear for me. Thanks a lot.

2. its really helpful. god bless you. now finally i understood all the things in deep. loved your work

3. Can u please tell why u haven't considered U _ email as a primary key..It can also determine all the other attributes uniquely..

1. Thanks. That's right. We could also consider the mail as the key according to the sample data. But when you consider in real time, if you have a constraint such that mail should be unique, then it would work otherwise not.

4. This comment has been removed by the author.

5. Why not split Tabel city into a 3th table City - State? Since you have 1 city with the same state? You didn't remove redundancy this way?

1. For fitting into the screen, i left few information like the area name in the city. instead i used zip code to refer to that area. Your question is correct. If we consider the given table alone, then City table is not in 3NF because of transitive dependencies

6. Sir how can we get to the following set of fd's ?
Just user_id-> {all other attributes} would suffice and would uniquely identify here.
so why do we need the (zip->city,state) and (city->zip,state).
Thank you. And Great tutorial.

1. user_id alone can be the key. The identification of all functional dependencies will help in normalizing to 2nf, 3nf, etc. Zip->city state is a transitive dependency. If there is transitive dependencies then the table is not in 3nf. Note: city->zip state does not hold on this relation. hence i removed it.

2. I understood the basic concept. Thank you. :)

7. Very informative..thanks a lot..I have understood it clearly

8. i guess there is transitive dependency in city table
zip -> city,state
city -> state
once check it

1. Thanks Jayaprakash. I have not considered city -> state. The reason is that there may be a city with the same name as that of the other in same state or different state. If you consider city as unique attribute, your point is correct

9. if i want to make diagram between the two tables what is the primary key and foreign key

1. Which diagram you are mentioning about? I would take it as ER diagram. The first property about connecting two relations is type of relationship. If the relationship type is many-to-many, then you have to create third table. In all the other cases, you can directly connect.
If you want to connect two tables, then in most of the cases, one of those tables will be ONE side table, and the other one will be MANY side table. The primary key of ONE side table will be included as FOREIGN key of MANY side table. If you can't understand, please refer here 'How to reduce an ER diagram to relation schemas - http://www.exploredatabase.com/2018/01/reduce-erd-with-many-relationships-to-schema.html' or else please contact me.

10. Thank a lot

11. Thanks for writing such a good article, I stumbled onto your blog and read a few post. I like your style of writing... Chi-squared distribution

12. Convert it to one level higher normal form than the existing one

1. To convert it to BCNF? City table is already in BCNF because the LHS of all FDs are candidate keys. Likewise, User_Personal table is also in BCNF. If we consider email as unique and still the property "the LHS should be candidate key" is true for user_personal. Hence, it is also in BCNF.

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