Join clicks and products to find DAU/MAU ratio

Last updated: November 20, 2025

Quick Overview

Write a query joining clicks and events to produce the combined DAU/MAU ratio.

Expedia

Data Manipulation (SQL/Python)

Data Scientist

Expedia

November 20, 2025

Data Scientist

Onsite

Data Manipulation (SQL/Python)

Hard

186

3,356 solved

Write a query joining clicks and events to produce the combined DAU/MAU ratio.

Expedia asks this during the Onsite because data engineering skills are critical for the role. You should be comfortable with complex joins, window functions, CTEs, and performance optimization.

What the Interviewer Expects

Solve complex analytical problems with elegant, readable SQL
Optimize queries for large-scale datasets with partitioning and indexing
Use recursive CTEs, lateral joins, and advanced window functions
Design the data model alongside the query solution
Discuss trade-offs between SQL and programmatic approaches (Python/pandas)
Consider the operational aspects: query scheduling, incremental processing

Key Topics to Cover

Window functions (ROW_NUMBER, RANK, LAG, LEAD)

Pandas vectorized operations and groupby

Data cleaning and transformation

NULL handling and COALESCE

Index optimization and query performance

How to Approach This

Clarify the schema and expected output format before writing queries.
Use CTEs (WITH clauses) to break complex queries into readable steps.
Consider window functions (ROW_NUMBER, RANK, LAG, LEAD) for ranking and sequential analysis.
Watch for NULLs, duplicates, and edge cases in JOINs and GROUP BY.
For pandas, prefer vectorized operations over row-by-row iteration.

Possible Follow-up Questions

What would you do if this query needs to run every 5 minutes?
How would you optimize this query for a table with 100 million rows?
How would you handle this if the data was spread across multiple databases?
What indexes would you create to support this query?

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Practice SQL Problems

Sample Answer

Problem Understanding

In this problem, we need to analyze user engagement by calculating the Daily Active Users (DAU) and Monthly Active Users (MAU) ratios using two tables: clicks and events. The clicks table contai...

Approach

Join the Tables: Start by joining the clicks and events tables on the user ID and date fields to correlate clicks with user logins.
Aggregate DAU and MAU: Use GROUP BY to calculat...

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Expedia Data Scientist Interview Guide

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