ETL Testing Interview Questions

Generally, basic testing concepts remains same across all domains. So, the basic testing questions will also remain same. The only addition would be some questions on domain. e.g. in case of ETL testing interview questions, it would be some concepts of ETL, how to’s on some specific type of checks / tests in SQL and some set of best practices. Here is the list of some ETL testing interview questions:

Q. 1) What is ETL?
Ans. ETL – extract, transform, and load. Extracting data from outside source systems. Transforming raw data to make it fit for use by different departments. Loading transformed data into target systems like data mart or data warehouse.

Q. 2) Why ETL testing is required?

• To verify the correctness of data transformation against the signed off business requirements and rules.
• To verify that expected data is loaded into data mart or data warehouse without loss of any data.
• To validate the accuracy of reconciliation reports (if any e.g. in case of comparison of report of transactions made via bank ATM – ATM report vs. Bank Account Report).
• To make sure complete process meet performance and scalability requirements
• Data security is also sometimes part of ETL testing
• To evaluate the reporting efficiency

Q 3) What is Data warehouse?

Ans. Data warehouse is a database used for reporting and data analysis.

Q4) What are the characteristics of a Data Warehouse?

Ans. Subject Oriented, Integrated, Time-variant and Non-volatile

Q5) What is the difference between Data Mining and Data Warehousing?

Ans.Data mining – analyzing data from different perspectives and concluding it into useful decision making information. It can be used to increase revenue, cost cutting, increase productivity or improve any business process. There are lot of tools available in market for various industries to do data mining. Basically, it is all about finding correlations or patterns in large relational databases.
Data warehousing comes before data mining. It is the process of compiling and organizing data into one database from various source systems where as data mining is the process of extracting meaningful data from that database (data warehouse).

Q6. What are the main stages of Business Intelligence.

Ans. Data Sourcing –> Data Analysis –> Situation Awareness –> Risk Assessment –> Decision Support

Q7. What tools you have used for ETL testing?

1. Data access tools e.g., TOAD, WinSQL, AQT etc. (used to analyze content of tables)
2. ETL Tools e.g. Informatica, DataStage
3. Test management tool e.g. Test Director, Quality Center etc. ( to maintain requirements, test cases, defects and traceability matrix)

Below are few more questions that can be asked:
 What is Data Mart?
Q9. Data Warehouse Testing vs Database Testing
Q10. Who are the participants of data warehouse testing
Q11. How to prepare test cases for ETL / Data Warehousing testing?
Q12. What is OLTP and OLAP
Q13. What is look up table
Q14. What is MDM (Master data management)
Q15. Give some examples of real time data warehousing

Also there are some common questions on types of ETL testing & related SQL knowledge. You may refer to my earlier post on this – Types of ETL testing–What is covered in ETL testing

In my upcoming posts, I’ll try to cover all these topics in detail. Remember, the interviewer may go more deeper into evaluating your ETL knowledge depending upon the type & nature of the project or project requirement.

Rahnuma is a technical content writer at software testing stuff. A software engineer by degree and a dynamic content creator by passion, she brings to table over 3 years of writing experience in tech niche. Combining her enthusiasm for writing and technology, she loves to share her thoughts on the latest tech trends.

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