Calculate average revenue per date
Last updated: July 25, 2025
Quick Overview
Write a query to compute average revenue grouped by user, handling edge cases like nulls and duplicates.
Plaid
July 25, 202510
8
2,475 solved
Write a query to compute average revenue grouped by user, handling edge cases like nulls and duplicates.
Plaid 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
- 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 optimize this query for a table with 100 million rows?
- How would you handle slowly changing dimensions in this scenario?
- What would you do if this query needs to run every 5 minutes?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice SQL ProblemsSample Answer
Problem Understanding
The task is to compute the average revenue per user grouped by date. The relevant data likely resides in a table containing user transactions, which includes fields such as user_id, `transaction_dat...
Approach
To build the query, the following steps will be taken:
- Identify the Relevant Tables: Determine the main table containing the transaction data.
- Filter Out NULLs: Ensure that only non-null...
Submit Your Answer
