Understanding Denormalization in Relational Databases?

Question

Let's say I have tables like below in NF3

Table Name: Address

• line1
• line2
• state_id

Table Name: State

• id
• name
• country_id

Table Name: Country

• id
• name

Now I want to denormalize this table so that read will be faster and I don't need to JOIN multiple tables, but I couldn't able understand what is denormalization is.

Example 1) Do I need to keep tables like above in 3NF, and extra columns to Address like state_name, country_name so the resulting table looks like below.

Table Name Address

• line1
• line2
• state_name
• country_name
• state_id

Or

Example 2) Do I need to remove state_id from the Address table and keep state_name and country_name.

Table Name Address

• line1
• line2
• state_name
• country_name

From the above 2 examples, which is denormalization?

Answer 1

Quoting Wikipedia:

Denormalization is the process of trying to improve the read performance of a database, at the expense of losing some write performance, by adding redundant copies of data or by grouping data.

So, by adding state_name to the Address table, you have denormalized the database.

It doesn't matter whether you eliminate state_id or not. The simple act of added a column like state_name that has a lot of rows with the same value, makes the database denormalized.