Join users and messages to find engagement score
Last updated: March 9, 2026
Quick Overview
Write a query joining users and impressions to produce the combined engagement score.
Instacart
March 9, 20267
12
3,923 solved
Write a query joining users and impressions to produce the combined engagement score.
Data manipulation questions at Instacart 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
- Use advanced SQL features: window functions, CTEs, subqueries
- Write efficient queries that avoid common performance pitfalls
- Handle complex data transformations with multiple joins and aggregations
- Discuss indexing strategy and query optimization
- Address data quality issues: duplicates, missing values, outliers
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
- What indexes would you create to support this query?
- How would you handle slowly changing dimensions in this scenario?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we need to analyze the engagement score of users by joining two tables: users and impressions. The users table contains user-specific information, such as user ID, user name, an...
Approach
- Identify Relevant Columns: Determine the necessary columns from both
usersandimpressions. For instance, user ID fromusersand impression type/timestamp fromimpressions. - **Join Ta...
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