How do clustered and non-clustered indexes differ and when to use them?
This advanced question tests understanding of physical storage and query optimization strategies.
Why Interviewers Ask This
Indexing is critical for performance. Interviewers assess your ability to choose the right index type to optimize read speeds without sacrificing write performance or storage.
How to Answer This Question
Define clustered index as storing data in physical order (one per table), ideal for range scans. Define non-clustered as a separate structure (many allowed), good for point lookups. Recommend based on query patterns.
Key Points to Cover
- Clustered: physical order, one per table
- Non-clustered: separate structure, many allowed
- Range vs point lookup optimization
- Impact on write performance
Sample Answer
A clustered index stores table rows in the physical order of the index key, meaning the data pages are the index itself; there can be only one. It is ideal for range scans and primary key lookups. A non-clustered index i…
Common Mistakes to Avoid
- Thinking multiple clustered indexes exist
- Ignoring write costs
- Not considering selectivity
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