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Denormalization in SQL

Last Updated on December 8, 2023 by Ankit Kochar

Denormalization is a database design technique in SQL that involves intentionally introducing redundancy into a relational database by incorporating redundant or duplicated data. This departure from the traditional normalization process is driven by the goal of optimizing query performance, particularly in situations where read operations significantly outnumber write operations. Denormalization aims to reduce the complexity of queries, enhance data retrieval speed, and improve overall system performance. While it introduces redundancy, careful implementation of denormalization strategies can lead to more efficient and responsive database systems.

Why do we Denormalize Tables in SQL?

There are several reasons for denormalization to be performed in SQL with the prominent of them being to improve the query performance as referencing and referenced technique in the normalized table leads to slower performance whereas denormalized table has all the relevant data present in a single working table.

The reason for the fast queries is that denormalization reduces the number of joins on tables for a better query execution rate.

In the above illustration, there are two tables named Order and Category that are already normalized. Then they are denormalized further to have the result table that constitutes attributes of both the sub-tables merged into one. A similar process can be followed for denormalization in SQL. Given below is another example that can help you build a strong grip on the topic with a real-world IPL franchise example.

Suppose there is a table of players and a table consisting of their respective teams. We can refer to the team of the players by defining a foreign key to access them in a normalized state.

Table Name: Teams

Team ID Team Name
1 Mumbai Indians
2 Royal Challengers Bangalore
3 Chennai Super Kings
4 Kolkata Knight Riders
5 Rajasthan Royals
6 Kings XI Punjab
7 Delhi Capitals
8 Sunrisers Hyderabad

Table Name: Players

Player ID Player Name Team ID
1 Rohit Sharma 1
2 Virat Kohli 2
3 MS Dhoni 3
4 Dinesh Karthik 4
5 Steve Smith 5
6 KL Rahul 6
7 Rishabh Pant 7
8 David Warner 8

Thus, if we want to achieve better access time then we can denormalize this row to create duplicates of the data from the other table into one. On the denormalized table, although access can be fast, updating can be tedious and time-consuming.

On the above two tables, we can implement the flattening technique to denormalize both tables.

Team ID Team Name Player Name Player ID
1 Mumbai Indians Rohit Sharma 1
2 Royal Challengers Bangalore Virat Kohli 2
3 Chennai Super Kings MS Dhoni 3
4 Kolkata Knight Riders Dinesh Karthik 4
5 Rajasthan Royals Steve Smith 5
6 Kings XI Punjab KL Rahul 6
7 Delhi Capitals Rishabh Pant 7
8 Sunrisers Hyderabad David Warner 8

The above contains all the attributes that were part of multiples tables of the normalized data. Here they are merged into one to denormalize the data.

Advantages and Disadvantages of Denormalization

Now that some of the key concepts about denormalization in SQL are clear to us, let us look at the pros and cons of the same given below:-


  • It can provide quick and efficient access.
  • Retrieving data is simple and easy.
  • Fewer tables need to be checked.


  • Redundant data can lead to data inconsistencies.
  • Updation and Insertion of data can be costly.
  • Not optimized for the storage of data, unlike normalized tables.

In conclusion, denormalization in SQL represents a deliberate deviation from the principles of normalization, prioritizing read performance over minimizing redundancy. By strategically duplicating data and simplifying query structures, denormalization can enhance the efficiency of database systems, especially in scenarios where complex joins and relationships impact query speed. However, it requires thoughtful consideration and trade-offs, as it can lead to increased storage requirements and potential challenges in maintaining data consistency.

Frequently Asked Questions of Denormalization in SQL

Here are some of the FAQs related to Denormalization in SQL:

Q1: What is the primary motivation behind denormalization in SQL databases?
The main motivation for denormalization is to improve query performance by reducing the complexity of joins and speeding up data retrieval, particularly in scenarios where read operations are more frequent than write operations.

Q2: In what situations is denormalization most beneficial?
Denormalization is most beneficial in scenarios where complex joins and relationships in normalized databases significantly impact query performance. It is often applied to reporting databases, data warehouses, or read-heavy applications.

Q3: What are the potential drawbacks of denormalization?
Denormalization introduces redundancy, leading to increased storage requirements and the potential for data inconsistency if updates are not carefully managed. It may also complicate data maintenance tasks.

Q4: How does denormalization differ from normalization in database design?
Normalization is a database design technique that minimizes redundancy and dependency by organizing data into separate tables, while denormalization introduces redundancy intentionally to optimize query performance.

Q5: Are there specific SQL commands or techniques for implementing denormalization?
Denormalization is not achieved through specific SQL commands but involves strategic design decisions. Common techniques include incorporating redundant columns, using materialized views, and precomputing aggregates to simplify queries.

Q6: Can denormalization be applied to all types of databases and scenarios?
Denormalization is not universally applicable and should be considered based on specific use cases. It is generally more suitable for read-heavy scenarios, such as reporting databases, data warehouses, or analytical applications.

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