Join impressions and messages to find engagement score
Last updated: July 3, 2025
Quick Overview
Write a query joining impressions and impressions to produce the combined engagement score.
xAI
July 3, 202528
7
399 solved
Write a query joining impressions and impressions to produce the combined engagement score.
Data manipulation questions at xAI test your ability to work with real-world datasets. This Phone Screen question evaluates your SQL proficiency, understanding of data modeling, and ability to derive insights from raw data.
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 optimize this query for a table with 100 million rows?
- How would you handle this if the data was spread across multiple databases?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
To determine the engagement score for users, we need to join two datasets: impressions and messages. The impressions table contains records of how many times a user saw content, while the `messa...
Approach
- Identify the tables: We will be working with the
impressionsandmessagestables. - Determine the join type: Since we want to include all users from the
impressionstable even if the...
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