Intermediate~3h
Window Functions in SQL & DatabasesInterview Readiness Check
ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, running totals, and the LAST_VALUE frame gotcha.
row_numberrankdense_ranklagleadpartition byoverrunning totalntile
Learning path
Try a sample question
Three employees have salaries: Alice 100k, Bob 100k, Carol 90k. ROW_NUMBER() assigns: 1, 2, 3 RANK() assigns: 1, 1, 3 DENSE_RANK() assigns: 1, 1, 2 Why does RANK() skip 2 but DENSE_RANK() does not?
A.RANK() counts all rows scanned so far; DENSE_RANK() counts only distinct salary values seen
B.ROW_NUMBER() determines the sequence that RANK() inherits
C.DENSE_RANK() is only for unique values; RANK() handles duplicates
D.RANK() leaves a gap equal to the number of tied rows before it; DENSE_RANK() always increments by exactly 1 regardless of ties
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What this module tests
- Conceptual understanding of window functions fundamentals
- Trade-offs and design decisions in real system scenarios
- row_number and rank — applied knowledge
- Interview-style reasoning and explanation quality
Free to start
Take the Window Functions check →
10 questions · Dimension scoring · AI coach feedback · Shareable result
Test your knowledge — free →No credit card · Takes 10–15 min
Frequently asked questions
- What does the Window Functions check test?
- The check covers row_number, rank, dense_rank, lag, lead, running totals, and the last_value frame gotcha. Questions span beginner to advanced difficulty and test both conceptual understanding and practical trade-off reasoning.
- What keywords should I know for Window Functions?
- Key concepts include: row_number, rank, dense_rank, lag, lead, partition by, over, running total, ntile. These frequently appear in sql & databases interviews at product and infrastructure companies.
- How many questions are in the check?
- Each check has 10 questions — a mix of MCQ and short-answer. You get scored by dimension (e.g., scalability, consistency) so you know exactly where to focus.
- How long does it take to study Window Functions?
- Most engineers spend around 3 hours on this module. The check itself takes about 10–15 minutes. You can retake it up to 3 times per day.
- What prerequisite knowledge do I need before Window Functions?
- Window Functions builds on Aggregations & Grouping. Complete those first for the best results.
- Is row_number, rank, dense_rank covered?
- Yes. The Window Functions module covers row_number, rank, dense_rank among other key concepts. The check includes questions that reflect real sql & databases interview patterns.