Calculate percentile rank per date

Last updated: April 4, 2026

Quick Overview

Write a query to compute percentile rank grouped by date, handling edge cases like nulls and duplicates.

Dropbox

Data Manipulation (SQL/Python)

Data Scientist

Dropbox

April 4, 2026

Data Scientist

Take-home Project

Data Manipulation (SQL/Python)

Easy

2,742 solved

Write a query to compute percentile rank grouped by date, handling edge cases like nulls and duplicates.

This question from Dropbox's Take-home Project 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

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

Window functions (ROW_NUMBER, RANK, LAG, LEAD)

JOIN types and when to use each

Aggregate functions and GROUP BY

Index optimization and query performance

Common Table Expressions (CTEs)

Subqueries and correlated subqueries

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 validate the correctness of your query results?
How would you optimize this query for a table with 100 million rows?
How would you handle slowly changing dimensions in this scenario?
Can you rewrite this without using subqueries?

Sharpen Your Skills on Codemia

Practice similar problems with our interactive workspace, get AI feedback, and track your progress.

Practice SQL Problems

Sample Answer

Problem Understanding

We are tasked with calculating the percentile rank of values grouped by date. The dataset involves a table containing at least two columns: date (the date of the record) and value (the numeric val...

Approach

Identify the Columns: Determine the columns in the dataset that will be used, likely date and value.
Handle NULLs: Filter out NULL values from the value column since they cannot be...

Submit Your Answer

Markdown supported

Dropbox Data Scientist Interview Guide

Interview process, tips, and preparation timeline