Join orders and clicks to find DAU/MAU ratio
Last updated: February 13, 2026
Quick Overview
Write a query joining orders and orders to produce the combined DAU/MAU ratio.
Zscaler
Data Manipulation (SQL/Python)
Data Scientist
Zscaler
February 13, 2026Data Scientist
Take-home Project
Data Manipulation (SQL/Python)
Hard
28
6
3,009 solved
Write a query joining orders and orders to produce the combined DAU/MAU ratio.
This question from Zscaler's Take-home Project tests practical data skills. The interviewer wants to see clean, efficient queries that handle edge cases like NULLs, duplicates, and large datasets.
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
Aggregate functions and GROUP BY
Index optimization and query performance
Subqueries and correlated subqueries
Data cleaning and transformation
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
- How would you handle slowly changing dimensions in this scenario?
- How would you validate the correctness of your query results?
- What indexes would you create to support this query?
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Practice SQL ProblemsSample Answer
Problem Understanding
We need to calculate the Daily Active Users (DAU) and Monthly Active Users (MAU) ratios using two datasets: orders and clicks. The 'orders' table likely contains user orders with timestamps, while the...
Approach
- Identify the tables and relevant columns: Determine the user identifier and timestamp columns from both the 'orders' and 'clicks' tables.
- Calculate DAU and MAU: We will use `COUNT(DISTI...
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