What Is ELT (Extract, Load, Transform)?

June 11, 2024

ELT (Extract, Load, Transform) is a data integration process commonly used in data warehousing and analytics. In this method, raw data is first extracted from various sources and then loaded into a destination system, such as a data warehouse or data lake. Once the data is in the destination, it is transformed into a suitable format for analysis and reporting.

what is elt

What Is ELT?

ELT, which stands for Extract, Load, Transform, is a data integration process used primarily in data warehousing and analytics. It involves three main stages: extraction, loading, and transformation of data. Initially, data is extracted from various source systems, which can include databases, applications, and flat files. This raw data is then loaded into a destination system, typically a data warehouse or data lake, without any prior transformation.

Once the data resides in the destination system, it undergoes transformation. The transformation process involves cleaning, structuring, and converting the data into a suitable format for analysis and reporting. This method leverages the computational power and storage capabilities of modern data platforms to handle the transformations, allowing for scalability and efficiency in processing large volumes of data.

What Is the Difference Between ELT and ETL?

The primary difference between ELT (Extract, Load, Transform) and ETL (Extract, Transform, Load) lies in the sequence and location of data transformation. In ETL, data is first extracted from source systems, transformed into a desired format or structure, and then loaded into a destination system, such as a data warehouse. This approach is useful when data needs to be cleaned and organized before being stored.

ELT involves extracting data and loading it in its raw form into the destination system, where the transformation takes place. This method leverages the processing power of modern data platforms to handle transformations, making it more scalable and efficient for large volumes of data. ELT is particularly suited for big data environments and real-time analytics, as it allows for flexible and on-demand data processing.

How Does ELT Work?

ELT (Extract, Load, Transform) works through three distinct stages.


In this initial stage, data is gathered from various source systems, which can include databases, applications, APIs, and flat files. The extraction process focuses on collecting raw data without modifying its structure or format. The goal is to obtain a comprehensive dataset that includes all relevant information needed for analysis.


Once the data is extracted, it is loaded into the destination system, typically a data warehouse or data lake. During this stage, the raw data is stored in its original form. This direct loading allows for efficient handling of large volumes of data, as it minimizes the need for intermediate storage and processing. The destination system must be capable of handling diverse data types and large datasets.


After the data is loaded into the destination system, the transformation process begins. This stage involves cleaning, structuring, and converting the raw data into a format suitable for analysis and reporting. Transformations can include data normalization, aggregation, filtering, and enrichment. The destination system's computational power is utilized to perform these transformations, leveraging its ability to process large datasets efficiently. This stage allows for flexible and on-demand data processing and real-time analytics.

Which Tools Are Used for ELT?

Various tools are used for ELT processes, leveraging their capabilities to handle extraction, loading, and transformation of data efficiently. Some of the popular ELT tools include:

  • Google BigQuery. A fully managed data warehouse that supports ELT by allowing raw data to be loaded into the platform, where transformations are performed using SQL-based queries.
  • Amazon Redshift. A data warehouse service that facilitates ELT by enabling raw data to be loaded directly into the system, with transformations conducted using SQL commands and built-in functions.
  • Snowflake. A cloud-based data warehousing solution that provides robust tools for loading raw data and performing transformations within the platform.
  • Azure Synapse Analytics. Microsoft's integrated analytics service allows data to be loaded into the system and transformed using SQL-based queries and data processing capabilities.
  • Databricks. A unified analytics platform that combines data engineering and data science, supporting ELT by enabling data extraction, loading, and transformation within a scalable and collaborative environment.
  • Fivetran. An automated data integration tool that focuses on the extraction and loading stages of ELT, transferring data from various sources to a data warehouse for subsequent transformation.
  • Matillion. An ELT tool designed for cloud data warehouses, providing an intuitive interface for managing data extraction, loading, and transformation processes.

What Are ELT Use Cases?

ELT is widely used across various industries for different purposes, leveraging its ability to handle large volumes of data efficiently. Some common use cases include:

  • Big data analytics. ELT is ideal for big data environments where large datasets are extracted from multiple sources and loaded into data lakes or warehouses. Transformations are performed as needed, allowing for real-time analysis and insights.
  • Data warehousing. In traditional data warehousing, ELT allows organizations to load raw data into the warehouse and perform transformations directly within the warehouse environment, optimizing storage and processing resources.
  • Real-time data processing. ELT is used for real-time data processing scenarios, such as streaming analytics and real-time monitoring, where data needs to be quickly ingested and transformed to provide immediate insights and support decision-making.
  • Business intelligence (BI). ELT supports business intelligence applications by providing a flexible and scalable approach to data integration. Data from various sources is loaded into a central repository and transformed to create reports, dashboards, and visualizations for business analysis.
  • Data integration. ELT is used to integrate data from disparate sources, such as CRM systems, ERP systems, social media, and IoT devices, into a unified platform. This integrated data can then be transformed to meet the needs of different analytical and operational processes.
  • Cloud data migration. Organizations migrating to cloud-based data warehouses and lakes use ELT to move their on-premises data to the cloud. Raw data is loaded into the cloud environment, where it can be transformed to leverage cloud-native processing capabilities.
  • Machine learning and AI. ELT processes are used to prepare and transform large datasets required for machine learning and AI models. Data scientists can extract and load raw data into a platform where they perform complex transformations and feature engineering.
  • Regulatory compliance and reporting. ELT helps organizations comply with regulatory requirements by ensuring that data from various sources is accurately collected, loaded, and transformed to meet reporting standards and audit requirements.

What Are the Benefits of ELT?

ELT offers several benefits that make it a preferred approach for modern data integration and processing needs:

  • Scalability. ELT leverages the processing power of modern data warehouses and data lakes, allowing organizations to handle large volumes of data efficiently. This scalability is crucial for big data environments and growing datasets.
  • Performance. By offloading transformation tasks to powerful data platforms, ELT can significantly improve performance. Data transformations are executed within the data warehouse, reducing the need for intermediate data storage and processing.
  • Flexibility. ELT provides greater flexibility in data processing. Raw data is loaded into the destination system first, allowing for on-demand and iterative transformations. This flexibility is particularly beneficial for evolving business requirements and real-time analytics.
  • Cost efficiency. ELT can be more cost-effective as it reduces the need for extensive ETL infrastructure and intermediate storage solutions.
  • Simplified data management. With ELT, data management becomes simpler as raw data is centralized in the data warehouse or data lake. This centralization facilitates easier data governance, security, and compliance management.
  • Real-time data processing. ELT supports real-time data ingestion and processing, enabling organizations to perform real-time analytics and decision-making.
  • Enhanced data quality. ELT allows for comprehensive data quality checks and transformations within the data warehouse. By performing transformations post-load, organizations ensure data is clean, consistent, and suitable for analysis.
  • Integration with modern tools. ELT is compatible with a wide range of modern data tools and platforms, enabling seamless integration with cloud services, big data technologies, and advanced analytics solutions.
  • Streamlined development. ELT simplifies the development process by separating data extraction and loading from transformation. Developers can focus on building robust data pipelines without worrying about transformation complexities upfront.

What Are the Limitations of ELT?

While ELT offers many advantages, it also has certain limitations:

  • Complexity in transformations. Transforming data within the target system can be complex and may require advanced skills in SQL or other query languages. This complexity can lead to longer development times and increased potential for errors.
  • Performance issues. If the target system (e.g., a data warehouse) is not optimized for handling large-scale transformations, it can lead to performance bottlenecks. The system's resources may be strained, affecting overall performance and query response times.
  • Cost. Performing transformations in the cloud or on-premises data warehouses can incur significant costs, especially with large datasets and extensive transformation requirements. Cloud-based platforms often charge based on data storage and processing usage, leading to higher operational expenses.
  • Data quality and consistency. Ensuring data quality and consistency can be challenging when dealing with raw data. Since data is loaded before transformation, any issues with data quality need to be addressed during the transformation stage, which can be resource intensive.
  • Security and compliance. Handling raw data that may include sensitive information requires robust security measures to protect data integrity and privacy. Compliance with regulations such as GDPR or HIPAA add additional layers of complexity to the ELT process.
  • Scalability constraints. While ELT is generally scalable, the scalability depends on the capabilities of the target system. If the target system cannot scale effectively to handle increasing data volumes and transformation workloads, it can limit the overall scalability of the ELT process.
  • Dependency on target system. ELT processes are heavily dependent on the target system's capabilities. If the target system lacks advanced transformation functions or has limited processing power, it can restrict the types and complexity of transformations that can be performed.
  • Resource management. Managing and allocating resources for both the loading and transformation processes can be challenging. Inefficient resource allocation leads to suboptimal performance and increased costs.

Anastazija is an experienced content writer with knowledge and passion for cloud computing, information technology, and online security. At phoenixNAP, she focuses on answering burning questions about ensuring data robustness and security for all participants in the digital landscape.