BCG Data Engineer Interview Questions & Answers (2026)

BCG is known for rigorous data engineering interviews that focus on practical, production-level knowledge. With 36 questions in our vault, the most common category is SQL (14 questions). Difficulty breakdown: 8 easy, 9 medium, 19 hard. Expect system design and optimization questions at senior levels.

- **Q1**: What is the difference between repartition and coalesce in Apache Spark? - **Q2**: Write an SQL query to find the second-highest salary from an employee table. - **Q3**: What strategies can you use to handle skewed data in Spark? - **Q4**: Design a Delta table layout for mixed workload: point lookups by user_id, range scans by date, and full partition scans. Compare partitioning vs. Z-ordering—when to use each, and the rewrite cost trade-off. - **Q5**: Describe how to secure sensitive data in cloud storage solutions.

- **SQL**: 14 questions - **Spark/Big Data**: 10 questions - **System Design/Architecture**: 8 questions - **Cloud/Tools**: 2 questions - **General/Other**: 1 questions - **Python/Coding**: 1 questions

Focus on SQL questions first, as they dominate BCG's interview pattern. Practice the top-frequency questions below, then move to adjacent categories. For senior roles, expect 1-2 system design rounds.