Skip to content
HireKitAcademy

SQL Window Functions Interview Questions Interview Guide

10 interview questions with sample answers

10-12 hours
Prep Time
$130K-$210K
Salary
10
Questions

About This Role

Master SQL window functions: ranking, aggregation, analytic functions, and solving complex analytical queries efficiently.

Behavioral Questions (2)

Q1

Tell me about a complex SQL query you optimized using window functions.

Sample Answer:

Query calculating running totals and rankings for sales data. Original: multiple self-joins, slow. Refactored: ROW_NUMBER, SUM OVER, PARTITION BY. Query time: 45s -> 2s.

Q2

How have you debugged window function queries?

Sample Answer:

Verify PARTITION BY and ORDER BY clauses, check frame specification. Tested frame: UNBOUNDED PRECEDING to CURRENT ROW. Added debugging SELECT to validate window boundaries.

Technical & Situational Questions (4)

Q3

Explain ROW_NUMBER, RANK, DENSE_RANK. When would you use each?

Sample Answer:

ROW_NUMBER: unique sequential within partition. RANK: ties get same rank, gaps. DENSE_RANK: ties get same rank, no gaps. Use ROW_NUMBER for deduplication, RANK for competition scoring.

Q4

How do you calculate running totals with window functions?

Sample Answer:

Use SUM() OVER (PARTITION BY id ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW). Key: correct frame specification.

Q5

How would you use LAG/LEAD for time-series analysis?

Sample Answer:

LAG(value, 1) gets previous row, LEAD gets next row. Calculate differences: current - LAG. Identify anomalies by comparing to previous period.

Q6

Explain the difference between aggregate and analytic window functions.

Sample Answer:

Aggregate (SUM, COUNT) return single value per partition. Analytic (ROW_NUMBER, LAG, NTH_VALUE) return value per row. Use analytic to keep granularity.

FAQ

What's the difference between WHERE and HAVING with windows?
WHERE filters rows before windowing. HAVING filters aggregated results. In window queries, both apply differently depending on placement.
How do I use window functions across multiple partitions?
You can have multiple window clauses with different PARTITION BY and ORDER BY. Each window operates independently.
Can I nest window functions?
No direct nesting. Use subqueries or CTEs to compute first window, then apply another window on results.
How do I handle NULL values in window functions?
NULLS FIRST/LAST in ORDER BY, use COALESCE for default values, exclude NULLs with WHERE.

Ready to Apply? Use HireKit's Free Tools

AI-powered job search tools for SQL Window Functions Interview Questions

AI Interview Coach

Practice with HireKit's AI-powered interview simulator

Resume Template

Make sure your resume gets you to the interview

hirekit.co — AI-powered job search platform

Last updated on 2026-03-07