What is ETL and ELT

AWS By Oct 10, 2023 No Comments

What are ETL and ELT processes?

ETL and ELT are two data integration processes that extract data from source systems and load it into target databases or data warehouses. The key difference is when the data transformation occurs.

ETL Process

In the ETL process:

  1. Data is Extracted from source systems
  2. Data is Transformed in a staging area
  3. Loaded into the target data warehouse
  • Transformation occurs before loading the data
  • Best suited for smaller, structured data sets
  • Takes longer but results in cleaner data
  • Well suited for legacy databases

ELT Process

In the ELT process:

  1. Data is Extracted from source systems
  2. Data is Loaded directly into the target data warehouse
  3. Data is Transformed within the data warehouse
  • Transformation occurs after loading the data
  • Faster to implement
  • Handles large, structured and unstructured data
  • Faster load times
  • More cost efficient

When to Use ETL vs ELT

  • ETL is better for:
  • Integrating with legacy databases
  • Complex transformations
  • Experiments
  • ELT is better for:
  • Large data volumes
  • Real-time data access
  • Cloud data warehouses

In summary, the key difference between ETL and ELT is when the data transformation occurs – before loading in ETL, and after loading in ELT. ELT has become the more modern and scalable approach due to its ability to handle big data and provide faster access. However, ETL still has its uses for certain scenarios. Often organizations use a mix of both ETL and ELT processes.

What are the main differences between ETL and ELT?

When would you use an ETL process over ELT and vice versa?

What are some examples of tools for ETL and ELT?

What are the advantages of using the ETL process?

Advantages of ETL over ELT

ETL and ELT are two methods of data integration that involve extracting data from source systems, transforming it, and loading it into a data warehouse or data lake. The main difference is when the transformation occurs – in ETL, data is transformed before loading into the target system, while in ELT, data is loaded first and then transformed.

Here are some of the key advantages of ETL over ELT:

Better Data Quality

Since data is transformed before loading with ETL, the data that ends up in the data warehouse is already clean and structured. This leads to better data quality and more accurate insights.

With ELT, all data – including dirty data – is loaded first. The data then needs to be cleaned and transformed, which can be a complex and error-prone process.

Faster Query Performance

Since the data in an ETL pipeline is already transformed and structured, queries run faster compared to ELT. With ELT, data needs to be transformed on the fly for each query, which can slow down performance.

Better for Compliance

ETL provides a more secure way to handle sensitive data since transformations occur before the data is loaded into the data warehouse. This makes it easier to comply with regulations like GDPR, HIPAA, and CCPA.

With ELT, sensitive data is loaded into the data warehouse first, which poses compliance risks if not handled properly.

More Mature Technology

ETL has been around for decades, so there are many mature ETL tools available. ELT is a relatively new technology, so the available tools are still catching up.

Better for Complex Transformations

ETL is better suited for datasets that require complex transformations since the transformations are done in a staging area before loading. ELT works best for large volumes of data where simple transformations are needed.

In summary, the key advantages of ETL over ELT are better data quality, faster query performance, improved compliance, availability of mature tools, and suitability for complex data transformations. However, ELT provides benefits like faster load times, lower maintenance requirements, and ability to handle big data. So the choice between E

What are the advantages of using the ELT process?

Advantages of ELT Over ETL

ELT and ETL are two data integration approaches that differ in when the data transformation occurs. ELT stands for Extract, Load, Transform while ETL stands for Extract, Transform, Load.

The key advantages of ELT over ETL are:

Faster Loading Times

Since ELT loads the raw data into the data warehouse before transforming it, the loading time is faster. ETL has to transform the data before loading it, which takes more time.

Handles Large Data Volumes

ELT can handle large data volumes better since the transformation occurs within the data warehouse after the data is loaded. ETL has to transform large amounts of data before loading it, which can be resource intensive.

Supports Real-time Data Access

ELT allows for near real-time data access since the raw data is loaded into the data warehouse and then transformed. This means the transformed data is available sooner. ETL has to wait for the transformation to complete before the data is available.


ELT is more scalable since the data warehouse’s native processing capabilities are used for the transformation. ETL has to rely on external systems for transformation which may not scale as well.

Simpler Implementation

ELT is generally considered simpler to implement since there are fewer moving parts. ETL requires more complex staging and transformation systems before loading the data.

Cost Effective

ELT tends to be more cost effective due to the faster loading times, ability to handle large volumes of data, and simpler implementation. ETL solutions often require more hardware and resources.

In summary, the key advantages of ELT are the faster loading times, ability to handle large data volumes in real-time, greater scalability, simpler implementation and lower costs. These factors make ELT a better fit for modern data warehouses, data lakes and big data environments compared to traditional ETL approaches.

When would you recommend using ETL over ELT?

When would you recommend using ELT over ETL?

How does ETL improve data quality compared to ELT?

How does ETL impact query performance compared to ELT?

What types of data transformations is ETL better suited for?


  1. https://www.ibm.com/blog/elt-vs-etl-whats-the-difference/
  2. https://www.qlik.com/us/etl/etl-vs-elt
  3. https://www.snowflake.com/guides/etl-vs-elt
  4. https://aws.amazon.com/compare/the-difference-between-etl-and-elt/
  5. https://www.talend.com/resources/elt-vs-etl/

I'm Abhay Singh, an Architect with 9 Years of It experience. AWS Certified Solutions Architect.

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