What is the difference between RANK, DENSE_RANK, and ROW_NUMBER?
This question tests your mastery of ranking window functions. It checks how you handle ties and gaps in ranked sequences.
Why Interviewers Ask This
Ranking data is essential for reporting top performers or leaders. Interviewers ask this to ensure you understand how ties are handled differently by each function. Choosing the wrong rank function can skew analysis results significantly.
How to Answer This Question
Define ROW_NUMBER as assigning unique sequential numbers even to ties. Explain RANK as assigning the same rank to ties but leaving gaps. Describe DENSE_RANK as assigning the same rank to ties without leaving gaps. Provide a small numeric example to illustrate the difference.
Key Points to Cover
- ROW_NUMBER is unique for every row
- RANK leaves gaps after ties
- DENSE_RANK has no gaps after ties
Sample Answer
ROW_NUMBER assigns a unique sequential number to every row, breaking ties arbitrarily. RANK gives the same rank to tied rows but leaves gaps in the sequence, like 1, 1, 3. DENSE_RANK also gives the same rank to ties but…
Common Mistakes to Avoid
- Using ROW_NUMBER when ties should share a rank
- Confusing RANK and DENSE_RANK gap behavior
- Not ordering the window function correctly
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