**Architectural Logic**: Both enforce uniqueness; PK is primary identity; unique is secondary. **Primary Key**: One per table; unique; NOT NULL; default clustered (SQL Server). **Unique Key**: Multiple per table; can allow NULL (DB-dependent). **Use**: PK for identity; unique...
This medium-level SQL question appears frequently in data engineering interviews at companies like Gartner. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, sql) 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.
Architectural Logic: Both enforce uniqueness; PK is primary identity; unique is secondary. Primary Key: One per table; unique; NOT NULL; default clustered (SQL Server). Unique Key: Multiple per table; can allow NULL (DB-dependent). Use: PK for identity; unique for alternate identifiers (email, SSN). Best Practice: PK as main join key; unique for secondary lookups without duplicates. Both support referential integrity.
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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.