What is Normalization in SQL and what are its types?

Normalization in SQL

Normalization is the process of organizing a database in a way that reduces redundancy and dependency. It is an important aspect of database design that helps to improve the performance, security, and integrity of a database.

There are several types of normalization, and the most common ones are:

1. First Normal Form (1NF): This is the basic level of normalization. A table is in 1NF if it meets the following criteria:

• It has a unique primary key.
• It has no repeating groups.

For example, consider a table called “Employees” with the following columns: EmployeeID (primary key), Name, Age, and PhoneNumbers. This table is not in 1NF because the “PhoneNumbers” column has repeating groups (i.e., an employee can have multiple phone numbers). To make this table 1NF, we can create another table called “PhoneNumbers” with the following columns: PhoneNumberID (primary key), EmployeeID (foreign key), and PhoneNumber. The original “Employees” table would then only contain the columns: EmployeeID (primary key), Name, and Age.

To create these tables in SQL, we can use the following commands:

CREATE TABLE Employees (
  EmployeeID INTEGER PRIMARY KEY,
  Name VARCHAR(255),
  Age INTEGER
);


CREATE TABLE PhoneNumbers (
  PhoneNumberID INTEGER PRIMARY KEY,
  EmployeeID INTEGER FOREIGN KEY REFERENCES Employees(EmployeeID),
  PhoneNumber VARCHAR(255)
)

2. Second Normal Form (2NF): A table is in 2NF if it is already in 1NF and all non-key columns are dependent on the entire primary key.

For example, consider the “Employees” and “PhoneNumbers” tables from the previous example. The “PhoneNumbers” table is not in 2NF because the “PhoneNumber” column is dependent on only part of the primary key (i.e., the EmployeeID column). To make this table 2NF, we can create another table called “PhoneNumberTypes” with the following columns: PhoneNumberTypeID (primary key), PhoneNumberID (foreign key), and PhoneNumberType. The “PhoneNumbers” table would then only contain the PhoneNumberID (primary key) and PhoneNumber columns.

To create these tables in SQL, we can use the following commands:

CREATE TABLE PhoneNumberTypes (
  PhoneNumberTypeID INTEGER PRIMARY KEY,
  PhoneNumberID INTEGER FOREIGN KEY REFERENCES PhoneNumbers(PhoneNumberID),
  PhoneNumberType VARCHAR(255)
);


ALTER TABLE PhoneNumbers
DROP COLUMN PhoneNumberType

3. Third Normal Form (3NF): A table is in 3NF if it is already in 2NF and all non-key columns are dependent on the primary key only.

For example, consider the “Employees”, “PhoneNumbers”, and “PhoneNumberTypes” tables from the previous example. The “PhoneNumberTypes” table is not in 3NF because the “PhoneNumberType” column is dependent on both the PhoneNumberID and the PhoneNumberTypeID columns. To make this table 3NF, we can create another table called “PhoneNumberTypeLookup” with the following columns: PhoneNumberTypeID (primary key) and PhoneNumberTypeDescription. The “PhoneNumberTypes” table would then only contain the PhoneNumberTypeID (foreign key) and

PhoneNumberID (foreign key) columns.

To create these tables in SQL, we can use the following commands:

CREATE TABLE PhoneNumberTypeLookup (
  PhoneNumberTypeID INTEGER PRIMARY KEY,
  PhoneNumberTypeDescription VARCHAR(255)
);


ALTER TABLE PhoneNumberTypes
DROP COLUMN PhoneNumberType

There are additional forms of normalization beyond 3NF, but they are less commonly used in practice.

It is important to note that normalization is a trade-off between the complexity of the database design and the performance of the database. In some cases, denormalizing a database (i.e., adding redundancy) can improve performance by reducing the number of joins required to retrieve data. However, this comes at the cost of increased storage and maintenance overhead.

Conclusion:

Normalization is a process that helps to organize and structure a database in a way that reduces redundancy and dependency. It is an important aspect of database design that can improve the performance, security, and integrity of a database. There are several types of normalization, including 1NF, 2NF, and 3NF, and each type builds upon the previous one to further reduce redundancy and dependency. Normalization is a trade-off between the complexity of the database design and the performance of the database, and in some cases, denormalizing a database can improve performance by reducing the number of joins required to retrieve data. However, this comes at the cost of increased storage and maintenance overhead.