**Natural keys**: Business identifiers (product_code, SSN); can change; composite; meaningful. **Surrogate keys**: System-generated (auto-increment, UUID); stable; single column; no business meaning. **Why surrogate for warehousing**: SCD Type 2 requires stable PK when natural...
This medium-level SQL question appears frequently in data engineering interviews at companies like BCG. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join) will help you answer variations of this question confidently.
Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.
Natural keys: Business identifiers (product_code, SSN); can change; composite; meaningful. Surrogate keys: System-generated (auto-increment, UUID); stable; single column; no business meaning. Why surrogate for warehousing: SCD Type 2 requires stable PK when natural key changes; simpler joins (single int vs. composite); hash-based dedup. Why keep natural: Validation, debugging, audit. Trade-off: Surrogate adds column; natural can leak PII. Cost: Surrogate join is faster (smaller key); SCD without surrogate needs complex merge logic.
Want feedback on your answer?
Paste your answer to this question and our AI Coach scores it, finds gaps, and shows you the FAANG-level version.
Get the most asked SQL questions with expert answers. Instant download.
No spam. Unsubscribe anytime.
Paste your answer and get instant AI feedback with a FAANG-level improved version.
Analyze My Answer — FreeAccording to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.