DataEngPrep.tech
QuestionsBlogStore
Get PDF Bundle
Home/Questions/SQL/Write a query to identify unique user sessions.

Write a query to identify unique user sessions.

SQLmedium0.2 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Wayfair
Key Concepts Tested
etlpartition
Expert AnswerPremium
49 wordsInterview-ready
If session_id exists: SELECT COUNT(DISTINCT session_id) AS unique_sessions FROM user_events. For session logic (30-min inactivity): Use LAG + CASE for session boundaries; SUM(session_flag) OVER (PARTITION BY user_id ORDER BY event_time) AS session_id. **Why**: Define session (time-based, event-based) consistently....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like Wayfair. The answer also includes follow-up discussion points that interviewers commonly explore.

Continue Reading the Full Answer

Unlock the complete expert answer with code examples, trade-offs, and pro tips - plus 1,863+ more.

Create Free Account - Unlock 30 Answers
Get PDF Bundle - from $21

Or upgrade to Platform Pro - $39

Engineers who used these answers got offers at

AmazonDatabricksSnowflakeGoogleMeta

Free: Top 20 SQL Interview Questions (PDF)

Get the most asked SQL questions with expert answers. Instant download.

No spam. Unsubscribe anytime.

Related SQL Questions

mediumWrite an SQL query to find the second-highest salary from an employee table.FreemediumDemonstrate the difference between DENSE_RANK() and RANK()FreemediumDiscuss differences between ROW_NUMBER(), RANK(), and DENSE_RANK(), and provide examples from your projects.FreemediumExplain the differences between Data Warehouse, Data Lake, and Delta LakeFreemediumExplain the differences between Repartition and Coalesce. When would you use each?Free

According to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

← Back to all questionsMore SQL questions →