Explain RANK, DENSE_RANK, and ROW_NUMBER differences
This tests ranking window functions. It is crucial for competitive analysis and leaderboard generation.
Why Interviewers Ask This
Ranking logic varies significantly between functions. Interviewers need to ensure candidates pick the right one for tie-breaking scenarios. Confusion here leads to incorrect analytics.
How to Answer This Question
Define ROW_NUMBER as unique sequential numbering with no ties. Define RANK as same rank for ties but gaps follow. Define DENSE_RANK as same rank for ties without gaps. Use a numerical example to clarify.
Key Points to Cover
- ROW_NUMBER is unique per row
- RANK has gaps after ties
- DENSE_RANK has no gaps
- Choice depends on tie handling
Sample Answer
ROW_NUMBER assigns a unique sequential number to each row, breaking ties arbitrarily. RANK assigns the same rank to tied rows but leaves gaps after ties (e.g., 1, 1, 3). DENSE_RANK also assigns the same rank to ties but…
Common Mistakes to Avoid
- Confusing RANK with DENSE_RANK
- Assuming ROW_NUMBER handles ties
- Not testing with duplicate values
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