11 ETL Interview Questions Along With Example Answers

By Indeed Editorial Team

Published 8 September 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.

ETL, or extract, transform and load, is a data integration process used in data warehousing. The ETL team ensures quality, records and secures data lineage, extracts data from the source and successfully provides data to end-user tools. Preparing answers to some questions that interviewers may ask can help you get a job as an ETL developer or a similar role. In this article, we look at some ETL interview questions and their answers and provide some helpful tips for a successful interview.

11 ETL Interview Questions And Answers

Here are some ETL interview questions with sample answers that can help you understand key concepts and prepare your own responses:

1. What do you understand about ETL?

Your interviewer may ask you this question to test your basic ETL knowledge. You can address this question directly and provide a brief answer. In your response, explain ETL's concept and process.

Example: 'ETL is a crucial element of a data warehousing architecture that controls the data for all business processes. Extract, transform and load is commonly known as ETL. Data from various sources combine through this data integration process. The data gets into a data warehouse or target systems from a single, consistent data store.'

Related: What Is ETL? (Definition, Importance And Prominent Uses)

2. What are the steps involved in an ETL process?

The ETL process primarily involves five steps. These five steps include extract, clean, transform, load and analyse, out of which extract, load and transform are the most important. You can briefly explain these steps.

Example: 'Although the abbreviation suggests a simple, three-step procedure, ETL involves more processes. Data extraction from various sources, transformation and loading into a data warehouse are all referred to as ETL. The final step in the process is data analyses.'

3. What is data warehousing and why is it important?

A data warehouse is a central repository of information, used to help decision-makers become more informed. Your interviewer can ask you this question to know your understanding of this concept. You can combine explaining data warehousing with its importance in your answer.

Example: 'Data warehousing is a crucial element of corporate intelligence. Analysts may work more efficiently, gain deeper insights and identify patterns across various datasets by combining several data sources under a single, unified library. It enhances firms' ability to make better decisions, making them more competitive.'

Related: What Is A Data Warehouse? (With Benefits And Uses)

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

Data mining refers to extracting crucial data from databases. Data warehousing is a technique for organising and compiling data into one database. You can explain the typical applications of data warehousing and the primary functions and differences between data mining and warehousing.

Example: 'Applications for data warehouses include information processing, analytical processing and data mining. Data warehousing may use a data mine for faster analytical data processing. In contrast, data mining is the process of extracting hidden predictive information from huge databases and interpreting the data. Data warehousing is the process of combining data from various sources into a single repository.'

Related: 13 Data Mining Techniques: A Complete Guide

5. What are the three tiers in ETL?

The interviewer may ask this question to assess your in-depth knowledge of the concept. In your answer, you can mention the different tiers of ETL architecture and briefly explain each.

Example: 'The data warehouse architecture consists of three tiers. The bottom tier consists of the data warehouse server, the middle tier consists of an OLAP server and the top tier contains front-end tools. The main advantage of a three-tier architecture is that each tier may get built simultaneously by a different development team and can get updated or scaled as required, this can get done without impacting the other tiers because each tier runs on its own infrastructure.'

Related: 6 Open-Source Data Profiling Tools (Benefits And Importance)

6. What are some of the common bugs in ETL?

A bug is a flaw, error or failure in the developed program or system that leads to unexpected results. Identifying, tracking and fixing bugs is essential to achieving the highest quality in the program or system. List the common bugs in your answer and maintain relevance.

Example: 'ETL testing can show a variety of problems, including data loss between the source system and the target system. It may also identify issues like inconsistent data across databases, long processing of queries, system failures resulting from the size of the data warehouse and graphical flaws in the font, colour or alignment.'

7. What is the difference between initial and incremental loads in ETL?

All additional data loads are incremental loads following the initial data load for a base object. Only updated or new data goes into the base object during this loading process. You can explain the functioning of these techniques.

Example: 'Initial load describes the procedure of initially loading all data from primary sources into the target system. After this, any additional system loads can be incremental, with only new or updated records added.'

Related: 11 Open Source ETL Tools For Business Data Integration

8. What are some of the best ETL features that our company ought to use?

This question may examine your knowledge about the company and their mechanisms. You can keep your answer straightforward and suggest a few steps the company can adopt. With your answer, assure your interviewer that you are the right candidate who makes informed decisions.

Example: 'The data integration process can be more effective and user-friendly with a competent ETL tool. Some ETL features you can include are compatibility with the cloud, enabling increased flexibility and easier management of large data and third-party integrations with BI tools and ERP platforms. You can also include automatic code generation to expedite the development and lower the risk of human error, a user-friendly interface to enhance the navigation and sophisticated debugging tools that minimise interruption of data flows.'

Related: 50 Informatica Interview Questions (With Example Answers)

9. What are the different types of partitioning in ETL and when can you use them?

Partitioning enhances performance and facilitates easy data management. It enables balancing several system requirements and optimises the hardware performance. In your answers, you can elaborate on the two types of partitioning.

Example: 'In ETL, there are two primary partitioning types, hash partitioning and round-robin partitioning. Hash partitioning assigns rows using a hash key. Partitions are dependent on the chosen hashing technique. In round-robin partitioning, rows get assigned in a round-robin fashion, meaning that roughly the same number of rows are present in each partition.'

10. What is meant by regression testing in ETL?

ETL regression testing aims to verify that the ETL produces the same output for a given input before and after the change. Any differences require verification to see if they are consistent with the changes. You can explain this in your answer.

Example: 'We use regression testing after creating functional fixes to the data warehouse. Its goal is to determine whether the repairs have negatively impacted other steps in the ETL process. After making changes to the system, regression testing determines whether any newly introduced flaws exist.'

11. When would you perform a lookup transformation in ETL?

The lookup transformation combines data from input columns with columns from a reference dataset to perform lookups. Using the lookup, you can retrieve more information from a related table based on values in standard columns. You can mention a situation for practical application.

Example: 'Lookup transformation retrieves values from a data source depending on certain lookup criteria. Situations such as updating a dimension table, checking pre-existing records in a table or finding a specific value from a table can utilise lookup transformation.'

Related: Useful Data Engineer Skills You Can Develop (With Steps)

Tips For A Successful ETL Interview

Here are a few tips that can help you create a positive impression during the interview:

  • Thoroughly research the company interviewing you. Having a basic knowledge of the company and its history is always helpful and analysing the company can help you highlight the value you may add to the organisation.

  • Work on your soft skills. Even with sound technical knowledge, it is essential to practise and improve your soft skills to make a good first impression on the interviewers.

  • Give mock interviews by listing answers to some ETL interview questions. Review them with your family members or friends and analyse the areas that require improvement.

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