Career
Interview preparation
No account needed for your first exercise. Questions and model answers are free to read; assessments need a free account.
Interview questions by topic
- Joins and referential integrity
Null keys, fan-out, orphans and how to prove a join didn't change your totals. · 10 questions
- Duplicates and survivor rules
Row grain, deterministic survivors and when a repeat is legitimate. · 10 questions
- Dates, times and time zones
Ambiguous formats, offsets, instants and daylight saving. · 10 questions
- Missing values
Missing versus empty versus zero, imputation and leakage. · 10 questions
- SQL cleaning and debugging
Casting, window functions, validation queries and reading someone else's query. · 10 questions
- pandas cleaning and debugging
Defaults that change data, nullable dtypes and merge validation. · 10 questions
- Clarifying questions and stakeholders
What to ask before cleaning, and how to explain a quarantine to a business owner. · 10 questions
- Data quality trade-offs
Delete, fix, flag or quarantine, and how to defend the choice. · 10 questions
Timed practice assessments
- Cleaning fundamentals
8 questions · 12 minutes
- Types, dates and money
8 questions · 12 minutes
- Joins and combining files
8 questions · 12 minutes
- Duplicates and entity resolution
8 questions · 10 minutes
- SQL cleaning check
8 questions · 10 minutes
- pandas cleaning check
8 questions · 10 minutes
Take-home practice
Each exercise is a take-home style task with stated rules, graded on hidden datasets. The interview-ready path sequences the ones interviewers ask about most, and the take-home guide covers what reviewers look for.
Practice assessments and model answers are for preparation only. They are not employer selection tests, they are not proctored, and they don't guarantee a job.