Denormalisation

It is a process during which you reduce the number of joins and remove normalisation of your data in a database, and introduces redundancy by combining tables. It helps with read performance thanks to the fact that you don’t have to perform expensive join queries.

Example
Normalised Schema:

SELECT orders.order_id, users.name, orders.total  
FROM orders  
JOIN users ON users.name = orders.user_id;  

Denormalised Schema:

SELECT order_id, user_name, total from orders;  

Pros:

• Faster queries
  Cons:
• Increases storage use
• Risk of inconsistency in data