SQL questions from EPAM data engineering interviews.
These sql questions are sourced from EPAM data engineering interviews. Each includes an expert-level answer. This set leans toward the medium-difficulty band most real interviews actually live in (8 of 14). Recurring themes are sql, join, and partition — these patterns appear most often in real interviews and reward the deepest preparation. Many of these questions also surface at Accenture and Cognizant, so the preparation transfers across companies. Average answer is around 1 minute of reading — plan roughly 1 hour to work through the full set thoughtfully.
This collection contains 14 curated questions: 2 easy, 8 medium, and 4 hard. The distribution skews toward harder problems, reflecting the depth expected in senior-level interviews.
The most frequently tested areas in this set are sql (6), join (6), partition (5), bigquery (3), snowflake (2), and optimization (2). Focusing on these topics will give you the highest return on your preparation time.
Start with the easy questions to warm up and solidify fundamentals. Medium-difficulty questions form the bulk of real interviews — spend the most time here and practice explaining your reasoning out loud. Hard questions often appear in senior and staff-level rounds; attempt them after you're comfortable with the basics. For each question, try answering before revealing the solution. Use our AI Mock Interview to simulate real interview conditions and get instant feedback on your responses.
Can you explain the difference between OLTP and OLAP?
Explain the concept of ACID properties in the context of databases.
Explain the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
How do you handle NULL values in SQL? Mention functions like COALESCE and NULLIF.
What is a Common Table Expression (CTE), and when would you use it?
What is the difference between a primary key and a unique key?
What is the difference between WHERE and HAVING clauses in SQL?
Describe a recent project where you used AWS services extensively. What was your role, and what challenges did you face?
Describe the process for migrating data from an on-premises SQL database to AWS. What services and strategies would you use?
Discuss a project where you significantly impacted performance or cost optimization.
Explain how you would implement partitioning and bucketing for data stored in S3 to improve query performance.
What challenges arise with duplicate records, and how do you address them?
What is your preferred location, and how soon can you join?
When would you choose partitioning over bucketing, or vice versa?
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