Write a query to find engagement score from impressions
Last updated: November 3, 2025
Quick Overview
Write a SQL query to calculate engagement score from the impressions table, considering nulls and duplicates.
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November 3, 202550
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Write a SQL query to calculate engagement score from the impressions table, considering nulls and duplicates.
This question from Zoom'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
- 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 handle this if the data was spread across multiple databases?
- How would you validate the correctness of your query results?
- What would you do if this query needs to run every 5 minutes?
- What indexes would you create to support this query?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to calculate the engagement score based on the data in the 'impressions' table. The engagement score can be defined as a ratio of unique engagements to total impressions within a specified...
Approach
- Identify Relevant Columns: Determine which columns are necessary for calculating the engagement score. This will likely include 'impression_id' for counting total impressions and 'user_id' for ...
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