Top Answers to ETL Testing Interview Questions

1. Compare ETL Testing & Manual Testing

CriteriaETL TestingManual testing
Basic procedureWriting scripts for automating testing processSeeing and testing method
RequirementsNo need of additional technical knowledge other than softwareNeed technical knowledge of SQL and shell scripting
EfficiencyFast, systematic and gives top resultsNeeds time, effort and prone to errors

2. What is ETL?

ETL refers to Extracting, Transforming and Loading of Data from any outside system to the required place. These are the basic 3 steps in the Data Integration process. Extracting means locating the Data and removing from the source file, transforming is the process of transporting it to the required target file and Loading the file in the target system in the format applicable.

3. Why ETL testing is required?

  • To keep a check on the Data which are being transferred from one system to the other.
  • To keep a track on the efficiency and speed of the process.
  • To be well acquainted with the ETL process before it gets implemented into your business and production.

Learn more about ETL testing process through this Data Warehouse Tutorial .


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4. What are ETL tester responsibilities?

  • Requires in depth knowledge on the ETL tools and processes.
  • Needs to write the SQL queries for the various given scenarios during the testing phase.
  • Should be able to carry our different types of tests such as Primary Key, defaults and keep a check on the other functionality of the ETL process.
  • Quality Check

5. What are the various tools used in ETL?

  • Cognos Decision Stream
  • Oracle Warehouse Builder
  • Business Objects XI
  • SAS business warehouse
  • SAS Enterprise ETL server

6. Define the ETL processing?

ETL Testing Process:
Although there are many ETL tools, there is a simple testing process which is commonly used in ETL testing. It is as important as the implementation of ETL tool into your business. Having a well defined ETL testing strategy can make the testing process much easier. Hence, this process need to be followed before you start the Data Integration processed with the selected ETL tool. In this ETL testing process, a group of experts comprising the programming and developing team will start writing SQL statements. The development team may customize according to the requirements.
ETL testing process is:
Analyzing the requirement – Understanding the business structure and their particular requirement.
Validation and Test Estimation – An estimation of time and expertise required to carry on with the procedure.
Test Planning and Designing the testing environment – Based on the inputs from the estimation, an ETL environment is planned and worked out.
Test Data preparation and Execution – Data for the test is prepared and executed as per the requirement.
Summary Report:  Upon the completion of the test run, a brief summary report is prepared for improvising and concluding.

To learn in more detail, check out ETL testing course.

7. Explain what are the ETL testing operations includes?

ETL testing includes

  •  Verify whether the data is transforming correctly according to business requirements
  • Verify that the projected data is loaded into the data warehouse without any truncation and data loss
  • Make sure that ETL application reports invalid data and replaces with default values
  •  Make sure that data loads at expected time frame to improve scalability and performance

8. Mention what are the types of data warehouse applications and what is the difference between data mining and data warehousing?

The types of data warehouse applications are:

  •  Info Processing
  • Analytical Processing
  • Data Mining
    –>Data mining can be define as the process of extracting hidden predictive information from large databases and interpret the data while data warehousing may make use of a data mine for analytical processing of the data in a faster way. Data warehousing is the process of aggregating data from multiple sources into one common repository.


9. What is fact? What are the types of facts?

It is a central component of a multi-dimensional model which contains the measures to be analyzed. Facts are related to dimensions.
Types of facts are:

  •  Additive Facts
  • Semi-additive Facts
  • Non-additive Facts

These are described in ETL Testing online reference guide and on ETL Testing community.

10. Explain what are Cubes and OLAP Cubes?

Cubes are data processing units comprised of fact tables and dimensions from the data warehouse.  It provides multi-dimensional analysis. OLAP stands for Online Analytics Processing, and OLAP cube stores large data in multi-dimensional form for reporting purposes.  It consists of facts called as measures categorized by dimensions.

11. List few ETL bugs.

  •  Calculation Bug
  • User Interface Bug
  • Source Bugs
  •  Load condition bug
  •  ECP related bug
    In addition to the above ETL testing questions, there may be other vital questions where you may be asked to mention the ETL tools which you have used earlier. Also, you might be asked about any debugging issues you have faced in your earlier experience or about any real time experience.

Interested in learning ETL bugs in more detail, click on ETL Tutorial blog.

3 thoughts on “Top ETL Testing Interview Questions And Answers”

  1. Thank you for sharing nice information.
    It is very useful to me and who are searching for Etl Testing online training

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