Write a query to find conversion rate from events
Last updated: May 31, 2026
Quick Overview
Write a SQL query to calculate conversion rate from the events table, considering nulls and duplicates.
Twilio
May 31, 20269
7
499 solved
Write a SQL query to calculate conversion rate from the events table, considering nulls and duplicates.
Twilio asks this during the Technical Screen 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
- Write syntactically correct SQL with proper JOIN and WHERE clauses
- Use GROUP BY and aggregate functions appropriately
- Handle NULL values correctly in your queries
- Explain the query execution plan at a high level
Key Topics to Cover
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 validate the correctness of your query results?
- What indexes would you create to support this query?
- How would you handle slowly changing dimensions in this scenario?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to calculate the conversion rate from the events table, which likely contains records of user interactions with the Twilio platform. Key data points involved are event types, specificall...
Approach
To build the SQL query, we can follow these steps:
- Identify conversion and non-conversion events: Use a WHERE clause to filter events based on their types.
- Aggregate data: Use COUNT to d...
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