Common ETL Interview Questions (With Example Answers)

By Indeed Editorial Team

Published June 9, 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

When applying for IT roles, it's important to create a strong impression during an interview. Your interviewer might ask you to demonstrate your technical knowledge of the extract, transform, and load (ETL) processes. Understanding common ETL interview questions can help you prepare appropriate answers for likely questions and increase your chances of getting the job. In this article, we outline common questions you can expect during an ETL interview, provide a list of answers to some common ETL interview questions, and review some interview tips.

ETL interview questions

ETL interview questions typically fall into three categories, including:

General interview questions

These questions are general queries that interviewers ask to gain insight into your values, interests, and habits. Some general interview questions include:

  • Can you tell us about yourself?

  • How did you learn about the open role in the company?

  • Can you describe yourself using three adjectives?

  • What is ETL?

  • What are your interests outside your profession?

  • What's your five-year plan?

  • How do you define success?

  • How best can you explain your work style?

  • What do you consider an ideal work environment?

  • What are your most identifiable weaknesses?

  • Can you describe some of your greatest strengths?

  • Why are you looking for a new role?

Experience and background questions

Interviewers ask these questions to learn more about your relevant academic qualifications and professional background. Some of these questions include:

  • Can you discuss your educational background and relevant experiences?

  • Do you prefer working with a team or individually?

  • Can you discuss some skills you learnt and developed other than your education and professional experience?

  • Can you tell us about a time you anticipated a problem and developed measures to prevent it?

  • Can you describe a professional experience that changed your outlook on a topic?

  • Tell us about a time you made a mistake and how you rectified it.

  • Can you tell us about a professional or personal accomplishment you're most proud of in your life?

  • Why did you choose your training program, and what other programs did you consider?

  • How do you process the fixed-length flat file?

  • During your education, what course challenged you the most? And how did you handle this academic obstacle?

  • What's the day-to-day process in the ETL system?

  • If hired, what changes can you bring to the organization?

In-depth interview questions

Interviewers use these in-depth questions to determine your expertise and understanding of the extract, transform, and load processes. These questions are technical and typically require you to demonstrate your proficiency in handling databases and performing other functions. Some questions in this category include:

  • What are the initial load and full load?

  • What are the steps involved in an ETL process?

  • What are snapshots? Can you explain their characteristics?

  • What are the tiers in ETL?

  • What are the views? Can you explain a materialized view log?

  • Can you describe partitioning, round-robin partitioning, and hash partitioning?

  • How can you fine-tune mapping in ETL?

  • How do you analyze tables in ETL?

  • What are the differences between connected and unconnected lookup?

Answers to common ETL interview queries

Here are some sample answers to the common ETL interview queries to help you prepare for your own interview:

What is ETL?

Interviewers usually ask this question to determine your perception of ETL. Providing a detailed definition gives them enough information to assess your understanding of the concept. You can personalize your answer by focusing on and highlighting your preferences or integrating the company's data gathering techniques into your answer.

Example: "ETL is a form of data integration that refers to the three-phase process used to blend data from different sources. The three database functions are extract, transform, and load. These functions work as one tool for pulling data from a database and transferring it to another. The database administrator typically gathers the data from different sources in the extract stage. Then, in the transform stage, the administrator converts the extracted data into the required format so that they can place them in another database. Finally, they write the data into the new database in the loading stage."

Related: How to Become a Database Administrator (With Average Salary)

How do you process the fixed-length flat file?

Interviewers ask this question to test your expertise and knowledge of processing flat files. When answering the question, it's crucial to outline the process sequentially. You can also highlight some variables and how they affect the process.

Example: "A fixed-length file layout typically includes the file name, where the field begins, its data type, and its length. In some cases, it may include the end position. Where the end position isn't there, you can calculate it for each field depending on the beginning position and the length if the ETL tool requires it. The ETL tools may require you to input the flat file's fire layout manually.

After inputting the layout, the tool remembers it and expects the same layout every time it interacts with the flat file. When processing fixed-length flat files, it's essential to validate the data positions in the file to ensure they're accurate. A quick validation test assesses any date or time field to ensure it's valid. For example, if there's a shift in positions, the date field contains illogical numbers and alpha characters. You can also test other fields with specific domains in the same way."

What are the three tiers in ETL?

Interviewers ask this question to test your knowledge of ETL further. It's essential to use clear and concise language when answering this question. When highlighting the layers, consider including an explanation and the function of each.

Example: "Data warehouses typically have a three-tier structure. The first layer is where the data lands, and the administrator compiles the data from the different sources. The second layer is the integration layer, where they transform the data to fit the company's needs. The third layer is the dimension layer, where they store the information for internal use. Many businesses use the ETL process to combine transaction data from a warehouse and convert it into a format others can understand and use. You can also use it to collect and join data from external partners and consolidate data from business mergers."

Related: What Is a Database Server? (Tips, FAQs, and Examples)

What are the differences between unconnected and connected lookup?

Interviewers often ask this question to test your understanding of lookup transformations. You can compare both transformations when answering this question as you explain their differences. Highlight only vital differences to help keep your answer short and direct.

Example: "A significant difference between a connected and unconnected lookup is that in a connected lookup, you can return multiple columns inserted into the dynamic lookup cache or from the same row. In contrast, in an unconnected lookup, there's a designated return port that returns one column from each row. Another difference is that connected lookup participates in mapping, while you can use the unconnected lookup when applying the lookup function rather than an expression transformation while mapping. A connected lookup returns multiple values, whereas the unconnected lookup returns a single output."

Other ETL interview tips

Here are some other tips to help have a successful interview:

Be punctual

It's advisable to arrive at your interview venue on time. Being punctual is an excellent way of showing your professionalism to your potential employer. If the interview is physical, you can arrive at least 15 minutes before your interview. Join the meeting a few minutes before your allocated time in a virtual interview. Punctuality helps you get organized and appear calm before the interview starts. You can prepare for unfavourable circumstances such as traffic or slow network connection by preparing ahead.

Related: Interview Preparation Tips

Do your research

It's essential to research the company before your interview because knowledge about the company and industry can demonstrate your interest in the role. For example, you can review the company's website and social media pages to gain insight into the company's culture. In addition, read up on any new projects, accomplishments, awards, events, or initiatives, particularly those related to the role for which you're applying. Finally, you can practise incorporating this knowledge into your answers to show the interviewer that you studied the company.

Prepare questions

It's essential to prepare questions to ask the interviewer at the end of the interview. For example, you can prepare two or three questions related to the specific role, upcoming projects, career development, or the company's culture. Asking relevant questions can help you decide if the company is the right fit for you.

Follow up after the interview

Consider following up with the hiring manager after the interview. You can send a short e-mail to thank them for their time and identify the interview as a memorable experience. Following up after the interview may distinguish. You from other candidates. It's only appropriate to follow up if the company policies support it.

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