Explain the difference between RANK, DENSE_RANK, and ROW_NUMBER
This question tests ranking functions. It evaluates handling of ties in sorted data.
Why Interviewers Ask This
Ranking is common in reporting. Interviewers check if you know how ties are handled differently by each function.
How to Answer This Question
Define ROW_NUMBER as unique sequential. RANK leaves gaps after ties. DENSE_RANK fills gaps. Give a numerical example.
Key Points to Cover
- ROW_NUMBER is unique
- RANK leaves gaps
- DENSE_RANK fills gaps
- Handling ties
Sample Answer
ROW_NUMBER assigns a unique number to each row, breaking ties arbitrarily. RANK assigns the same rank to ties but leaves gaps (e.g., 1, 1, 3). DENSE_RANK also assigns the same rank to ties but doesn't leave gaps (e.g., 1, 1, 2).
Common Mistakes to Avoid
- Confusing RANK and DENSE_RANK
- Assuming ROW_NUMBER handles ties
- Not understanding gap generation
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