Calculate percentile rank per date
Last updated: March 1, 2026
Quick Overview
Write a query to compute percentile rank grouped by date, handling edge cases like nulls and duplicates.
OpenAI
March 1, 202624
8
3,861 solved
Write a query to compute percentile rank grouped by date, handling edge cases like nulls and duplicates.
This question from OpenAI's Phone Screen 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
- 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
- Can you rewrite this without using subqueries?
- 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
We need to compute the percentile rank of values grouped by date from a dataset. The data involved includes a date column and a value column, which may contain duplicates and NULLs. The expected outpu...
Approach
- Identify the Dataset: Ensure the dataset contains the necessary columns: 'date' and 'value'.
- Handle NULLs: Use
COALESCEto replace NULLs with a default value (e.g., 0) or exclude them...
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