Numerator Data Engineer Interview Questions + Guide in 2025

Numerator is a leading company in the advertising intelligence sector, providing insights and analytics that empower brands to make data-driven decisions.

As a Data Engineer at Numerator, you will play a crucial role in designing, building, and maintaining the data infrastructure necessary for processing large datasets that inform business strategies. Your key responsibilities will include developing scalable data pipelines, ensuring data quality and integrity, and collaborating with data scientists and analysts to optimize data usage. A strong proficiency in SQL and experience with various data processing frameworks (such as Apache Spark or Hadoop) are essential, along with familiarity with cloud platforms like AWS or Azure. Critical thinking, problem-solving abilities, and a passion for working with data will make you an excellent fit for this role, as Numerator values innovation and analytical rigor in its commitment to delivering actionable insights to its clients.

This guide will help you prepare effectively for your interview by providing insights into the skills and knowledge areas that Numerator emphasizes for the Data Engineer role, enabling you to showcase your capabilities confidently.

The interview process for a Data Engineer role at Numerator is structured and thorough, designed to assess both technical skills and cultural fit. The process typically unfolds in several key stages:

1. Initial Screening

The first step involves a phone screening with a recruiter or HR representative. This conversation usually lasts about 30 minutes and focuses on your background, experiences, and motivations for applying to Numerator. It’s an opportunity for the recruiter to gauge your fit for the company culture and the specific role.

2. Technical Assessment

Following the initial screening, candidates are often required to complete a technical assessment. This may take the form of an online coding test, which can include multiple-choice questions related to data engineering concepts, SQL queries, and algorithmic challenges. The assessment is designed to evaluate your foundational knowledge and problem-solving abilities in a timed environment.

3. Take-Home Assignment

In some cases, candidates may be asked to complete a take-home assignment. This task typically involves a real-world data engineering problem that you will need to solve and present. While this step allows you to showcase your skills, be prepared for it to require more time than initially indicated, as the complexity of the assignment can vary.

4. Technical Interviews

Candidates who successfully pass the initial assessments will move on to one or more technical interviews. These interviews are often conducted by senior engineers or team leads and may include live coding exercises, system design questions, and discussions about your previous projects. Expect to engage in problem-solving discussions that test your understanding of data structures, algorithms, and best practices in data engineering.

5. Behavioral Interviews

In addition to technical evaluations, candidates will typically undergo behavioral interviews. These sessions focus on your past experiences, teamwork, and how you handle challenges in a work environment. Interviewers may ask situational questions to assess your soft skills and cultural fit within the team.

6. Final Interview

The final stage often involves a wrap-up interview with higher management or team members. This may include a case study presentation where you discuss your approach to a specific problem or project. This is also a chance for you to ask questions about the team dynamics and company culture.

Throughout the process, communication with the HR team is generally consistent, providing updates and feedback at various stages.

As you prepare for your interviews, it’s essential to be ready for a mix of technical and behavioral questions that reflect the skills and experiences relevant to the Data Engineer role at Numerator.

Here are some tips to help you excel in your interview for the Data Engineer role at Numerator.

Understand the Interview Process

Familiarize yourself with the multi-step interview process that Numerator employs. Expect a combination of technical assessments, coding tests, and behavioral interviews. The process often includes an initial screening, followed by a cognitive assessment, and multiple rounds of technical interviews. Being aware of this structure will help you prepare effectively and manage your time during the interview.

Prepare for Technical Assessments

Given the emphasis on technical skills, ensure you are well-versed in SQL, data structures, algorithms, and system design. Practice coding problems on platforms like HackerRank or LeetCode, focusing on dynamic programming and data manipulation tasks. Be ready to explain your thought process during live coding sessions, as interviewers will likely ask you to solve problems in real-time.

Master the Take-Home Assignment

If you receive a take-home assignment, approach it with diligence. While some candidates have found the assignments vague or time-consuming, treat it as an opportunity to showcase your skills. Ensure you understand the requirements clearly and allocate sufficient time to complete it. Document your thought process and be prepared to discuss your approach during the review.

Communicate Effectively

During interviews, especially in behavioral rounds, articulate your experiences clearly. Use the STAR (Situation, Task, Action, Result) method to structure your responses. Be prepared to discuss past projects, challenges you faced, and how you resolved conflicts. This will demonstrate your problem-solving abilities and how you work within a team.

Emphasize Cultural Fit

Numerator values a collaborative and supportive work environment. Show your enthusiasm for teamwork and your ability to adapt to the company culture. Be prepared to discuss how you handle feedback, manage expectations, and contribute to a positive team dynamic. This will help you resonate with the interviewers and align yourself with the company’s values.

Stay Calm and Engaged

Interviews can be intense, but maintaining a calm demeanor will help you think clearly and respond effectively. Engage with your interviewers by asking insightful questions about the team, projects, and company culture. This not only shows your interest but also helps you gauge if Numerator is the right fit for you.

Follow Up Professionally

After your interviews, send a thank-you email to express your appreciation for the opportunity. This is a chance to reiterate your interest in the role and reflect on any key points discussed during the interview. A thoughtful follow-up can leave a lasting impression and demonstrate your professionalism.

By preparing thoroughly and approaching the interview with confidence, you can position yourself as a strong candidate for the Data Engineer role at Numerator. Good luck!

Technical Skills

1. Can you explain the differences between SQL and NoSQL databases?

Understanding the distinctions between SQL and NoSQL is crucial for a Data Engineer, as it impacts data modeling and storage decisions.

How to Answer

Discuss the fundamental differences in structure, scalability, and use cases for both types of databases. Highlight scenarios where one might be preferred over the other.

Example

"SQL databases are structured and use a predefined schema, making them ideal for complex queries and transactions. In contrast, NoSQL databases are more flexible, allowing for unstructured data and horizontal scaling, which is beneficial for handling large volumes of data in real-time applications."

2. Describe a challenging data pipeline you built. What were the key components?

This question assesses your practical experience in building data pipelines, which is a core responsibility of a Data Engineer.

How to Answer

Outline the problem you faced, the technologies you used, and the outcome of the project. Emphasize your role in the design and implementation phases.

Example

"I built a data pipeline that ingested real-time streaming data from IoT devices. I used Apache Kafka for data ingestion, Apache Spark for processing, and stored the results in a PostgreSQL database. This pipeline reduced data latency from hours to minutes, significantly improving our analytics capabilities."

3. How do you ensure data quality in your ETL processes?

Data quality is paramount in data engineering, and interviewers want to know your strategies for maintaining it.

How to Answer

Discuss the methods you use to validate and clean data during the ETL process, including automated testing and monitoring.

Example

"I implement data validation checks at each stage of the ETL process, using tools like Great Expectations to automate testing. Additionally, I monitor data quality metrics continuously to catch any anomalies early and ensure that the data remains reliable for analysis."

4. What is your experience with cloud data services?

Cloud platforms are increasingly used for data storage and processing, so familiarity with them is essential.

How to Answer

Mention specific cloud services you have used, such as AWS, Google Cloud, or Azure, and describe how you utilized them in your projects.

Example

"I have extensive experience with AWS, particularly with services like S3 for storage, Redshift for data warehousing, and Lambda for serverless processing. I recently migrated a legacy data warehouse to Redshift, which improved query performance and reduced costs."

Data Structures and Algorithms

1. How would you implement a stack using an array?

This question tests your understanding of fundamental data structures, which is essential for any engineering role.

How to Answer

Explain the concept of a stack and how you would manage the array's size, including push and pop operations.

Example

"I would create a class for the stack that includes an array to hold the elements and an integer to track the current size. The push operation would add an element to the end of the array, while the pop operation would remove the last element and return it, ensuring to check for underflow conditions."

2. Can you explain the concept of a linked list and its advantages over arrays?

Understanding linked lists is important for data manipulation and memory management.

How to Answer

Discuss the structure of a linked list and its benefits, such as dynamic sizing and ease of insertion/deletion.

Example

"A linked list consists of nodes where each node contains data and a reference to the next node. Unlike arrays, linked lists can grow and shrink dynamically, making them more efficient for scenarios where frequent insertions and deletions are required."

3. Describe a time when you optimized a slow-running query. What steps did you take?

This question evaluates your problem-solving skills and understanding of database performance.

How to Answer

Detail the specific query, the performance issues, and the optimizations you implemented, such as indexing or query rewriting.

Example

"I had a query that was taking over 10 seconds to run due to a lack of indexing. I analyzed the execution plan, identified the missing indexes, and added them. After implementing the changes, the query execution time dropped to under 1 second."

4. How would you approach solving a problem with a large dataset that doesn't fit into memory?

This question assesses your ability to handle big data challenges.

How to Answer

Discuss techniques such as data partitioning, using distributed computing frameworks, or leveraging cloud services.

Example

"I would use a distributed computing framework like Apache Spark to process the data in parallel across a cluster. By partitioning the dataset and using techniques like map-reduce, I can efficiently analyze large datasets without needing to load everything into memory at once."

Behavioral Questions

1. Describe a situation where you had to manage conflicting priorities from stakeholders.

This question evaluates your communication and project management skills.

How to Answer

Provide a specific example, focusing on how you prioritized tasks and communicated with stakeholders.

Example

"In a previous project, I had to balance requests from the marketing and product teams. I organized a meeting to understand their needs and then created a priority matrix to align our goals. By setting clear expectations and timelines, I was able to deliver on both fronts without compromising quality."

2. How do you handle feedback and criticism?

This question assesses your ability to grow and adapt in a professional environment.

How to Answer

Discuss your approach to receiving feedback and how you use it to improve your work.

Example

"I view feedback as an opportunity for growth. When I receive criticism, I take time to reflect on it and identify actionable steps I can take to improve. For instance, after receiving feedback on my presentation skills, I enrolled in a public speaking course, which significantly boosted my confidence and effectiveness in communicating complex ideas."

3. Can you give an example of a time you had to learn a new technology quickly?

This question evaluates your adaptability and willingness to learn.

How to Answer

Share a specific instance where you had to learn a new tool or technology under pressure and how you approached it.

Example

"When my team decided to adopt Apache Kafka for real-time data streaming, I had limited experience with it. I dedicated a weekend to online courses and hands-on practice, and by the following week, I was able to contribute to the implementation and even led a training session for my colleagues."

4. Tell me about a time you made a mistake and how you handled it.

This question assesses your accountability and problem-solving skills.

How to Answer

Be honest about the mistake, what you learned from it, and how you rectified the situation.

Example

"I once misconfigured a data pipeline, causing data loss for a day. I immediately informed my team and worked overtime to restore the lost data from backups. I also implemented additional checks to prevent similar issues in the future, ensuring better data integrity moving forward."