Write a query to find time to first action from messages
Last updated: July 27, 2025
Quick Overview
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
Morgan Stanley
July 27, 20253
7
2,459 solved
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
Data manipulation questions at Morgan Stanley test your ability to work with real-world datasets. This Technical 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
- How would you handle slowly changing dimensions in this scenario?
- Can you rewrite this without using subqueries?
- How would you validate the correctness of your query results?
- How would you handle this if the data was spread across multiple databases?
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Practice SQL ProblemsSample Answer
Problem Understanding
To solve the problem of calculating the time to first action from the messages table, we need to understand the structure of the data involved. The messages table likely contains fields such as `messa...
Approach
- Identify Relevant Columns: Focus on
user_id,timestampfor messages, andaction_typewith its correspondingtimestampfor actions. - Remove Duplicates: Use a CTE to select only the...
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