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Primary Key vs. Secondary Key?

General/Othereasy0.4 min readPremium

PRIMARY KEY: Unique identifier; one per table; NOT NULL; used for FKs. SECONDARY KEY: Non-primary unique (e.g., email, passport); can have multiple; supports lookups. WHY: PK enables referential integrity; secondary keys support alternate access paths. SCALABILITY: Index on PK...

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Frequency
Low
Asked at 1 company
Category
243
questions in General/Other
Difficulty Split
151E|43M|49H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Altimetrik

Why This Question Matters

This easy-level General/Other question appears frequently in data engineering interviews at companies like Altimetrik. While less common, it tests deeper understanding that distinguishes strong candidates.

How to Approach This

Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.

Expert Answer
71 words

PRIMARY KEY: Unique identifier; one per table; NOT NULL; used for FKs. SECONDARY KEY: Non-primary unique (e.g., email, passport); can have multiple; supports lookups. WHY: PK enables referential integrity; secondary keys support alternate access paths. SCALABILITY: Index on PK is default; secondary keys need explicit indexes. COST: More indexes = slower writes, more storage; choose based on query patterns. TRADE-OFF: Surrogate keys (auto-increment) when natural keys are composite or may change.

The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations covering performance optimization and real-world examples.

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According to DataEngPrep.tech, this is one of the most frequently asked General/Other 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.

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