stratascratch.com

# StrataScratch

> Data science interview preparation: coding questions asked in real
> interviews at Amazon, Meta, Google and others, solved against live
> datasets in the browser, plus guides, learning paths and a blog on SQL,
> Python and analytics.

The site spans two hosts. This one carries the written material. The
practice questions live on https://platform.stratascratch.com and are listed in its own
llms.txt.

## Practice

- [Coding questions](https://platform.stratascratch.com/coding): SQL and Python questions from real interviews, run against the dataset in the browser
- [Data projects](https://platform.stratascratch.com/data-projects): End-to-end projects worked in a notebook
- [Pricing](https://platform.stratascratch.com/pricing)

## Learning paths

- [All learning paths](https://www.stratascratch.com/learn)
- [Comprehensive SQL](https://www.stratascratch.com/learn/comprehensive-sql): Master SQL from foundations to advanced window functions. 6 modules covering everything you need for data analyst interviews.
- [Comprehensive Python](https://www.stratascratch.com/learn/comprehensive-python): Learn Python for data analysis. Covers pandas, data wrangling, and common interview patterns.

## Guides

- [All guides](https://www.stratascratch.com/guides)
- [How to Make a Boxplot with Matplotlib](https://www.stratascratch.com/guides/boxplot-with-matplotlib): Drawing a boxplot in Matplotlib is a valuable skill for visualizing data distribution. You’ll get all the fundamentals and a real-world example in this article.
- [A Complete Python Guide to Case Statements and Conditional Logic](https://www.stratascratch.com/guides/python-case-statements-and-conditional-logic): Mastering case statements in Python with best practices, alternatives, and real-life applications
- [The Ultimate FULL OUTER JOIN Guide: Syntax, Examples & Real-World Applications](https://www.stratascratch.com/guides/the-ultimate-full-outer-join-guide): From Basics to Advanced: In this guide, we’ll discuss how it works, when to use it, and give practical examples.
- [Mastering PySpark Joins: Learn the Logic, Avoid the Traps](https://www.stratascratch.com/guides/mastering-pyspark-joins): Master Inner, Left, and Complex Joins in PySpark with Real Interview Questions
- [Machine Learning Modeling: Essential Techniques, Tools, and Examples](https://www.stratascratch.com/guides/machine-learning-modeling): Machine learning modeling is intimidating for beginners. Here, we’ll make it less complicated and guide you through essential modeling techniques.
- [Looping Through Lists in Python](https://www.stratascratch.com/guides/looping-through-lists-in-python): Go beyond basic examples and explore how looping through lists in Python helps solve real data challenges.
- [T-Test or Z-Test for Python: Which Should You Use?](https://www.stratascratch.com/guides/t-test-or-z-test): Statistical thinking is more than just math - it’s a decision-making toolkit.
- [SQL Data Manipulation for Data Scientists](https://www.stratascratch.com/guides/sql-data-manipulation-skills): 9 practical modules in SQL from advanced data transformations to financial reporting particularities for starting your career in data science
- [Python Data Manipulation for Data Scientists](https://www.stratascratch.com/guides/python-data-manipulation-skills): 9 practical modules in Python from advanced data transformations to financial reporting particularities for starting your career in data science!
- [SQL Time&Date Manipulation for Data Scientists](https://www.stratascratch.com/guides/sql-time-and-date-skills): 8 practical modules in SQL from time arithmetics to time series analysis for starting your career in data science
- [Python Time&Date Manipulation for Data Scientists](https://www.stratascratch.com/guides/python-time-and-date-skills): 8 practical modules in Python from time arithmetics to time series analysis for starting your career in data science

## Blog

- [Blog home](https://www.stratascratch.com/blog)
- [Full archive](https://www.stratascratch.com/blog/archive)
- [Career articles](https://www.stratascratch.com/blog/categories/career)
- [Interviews articles](https://www.stratascratch.com/blog/categories/interviews)
- [Guides articles](https://www.stratascratch.com/blog/categories/guides)
- [Companies articles](https://www.stratascratch.com/blog/categories/data-science-companies)
- [Technical Topics articles](https://www.stratascratch.com/blog/categories/topics)
- [Product Updates articles](https://www.stratascratch.com/blog/categories/product-updates)

## Recent articles

- [Top 10 Data Science Project Platforms to Build Your Portfolio](https://www.stratascratch.com/blog/top-10-data-science-project-platforms-to-build-your-portfolio): An inadequate portfolio is one of the main reasons you don't get an interview. These 10 data science project platforms will help your portfolio stand out.
- [AI in Data Science: How Experts Decide What to Automate](https://www.stratascratch.com/blog/ai-in-data-science-how-experts-decide-what-to-automate): Learn how experts use AI in data science, which tasks they automate, where human judgment still matters, and how the AI data scientist workflow is evolving.
- [Meet StrataAI: Your Built-In Coding Tutor on StrataScratch](https://www.stratascratch.com/blog/meet-strataai): StrataAI is StrataScratch’s new AI coding tutor. See how it explains questions, gives hints, and debugs your code without ever handing you the full answer.
- [50 LLM Interview Questions and Answers for 2026](https://www.stratascratch.com/blog/50-llm-interview-questions-and-answers): Beginner to advanced LLM interview questions with real practice and system design.
- [How AI Changed the Data Science Interview](https://www.stratascratch.com/blog/how-ai-changed-the-data-science-interview): The data science job changed. Job interviews changed. Did you adapt, or are you still preparing for an interview that no longer exists?
- [StrataScratch’s Data Project and Mini-Analysis Grader and Evaluator](https://www.stratascratch.com/blog/data-project-and-mini-analysis-grader-and-evaluator): Every data project and mini-analysis you submit gets read by an AI that scores five dimensions, catches six cardinal sins, and refuses – on principle – to hand you the fix.
- [StrataScratch Mini Analyses: Bite-Sized Real-World Data Analysis Practice](https://www.stratascratch.com/blog/what-are-mini-analyses): StrataScratch's new question format pairs a small, uncleaned dataset with a real business scenario — testing the judgment calls that separate a working analyst from someone who can just write a query.
- [How to Connect StrataScratch to Claude Using an MCP Connector](https://www.stratascratch.com/blog/how-to-connect-stratascratch-to-claude-using-an-mcp-connector): Connect your StrataScratch account to Claude with the StrataScratch public MCP connector. Browse interview questions, run code against real datasets, check your solutions, and review your progress, all without leaving your chat window.
- [Using SQL Regex to Classify and Filter Messy Data](https://www.stratascratch.com/blog/using-sql-regex-to-classify-and-filter-messy-data): Messy ratings, jumbled addresses, and buried keywords: SQL regex filters and classifies all of it inside the query, in seven real interview questions.
- [How SQL EXISTS Works and When to Use It](https://www.stratascratch.com/blog/how-sql-exists-works): Ignore EXISTS at your own peril! Learn how SQL EXISTS actually works, how it compares to IN and JOIN, and solve actual interview questions.
- [SQL Execution Order Explained With Real Query Examples](https://www.stratascratch.com/blog/sql-execution-order-explained): SQL execution order decides how queries actually run. Learn why FROM comes first, how aliases fail in WHERE, and when to use HAVING, with real examples.
- [You’re Not Unemployed. You’re Unemployable. (Here’s Why.)](https://www.stratascratch.com/blog/you-are-not-unemployed-you-are-unemployable): Five reasons your data science job search isn't working, and what to fix before sending another application.
- [Understanding NULL Semantics in SQL](https://www.stratascratch.com/blog/understanding-null-semantics-in-sql): NULL in SQL is often a source of confusion, leading to bug propagation. Learning how NULL behaves in different scenarios to keep your query outputs trustworthy.
- [INTERSECT vs UNION in SQL for Reasoning About Overlapping Data](https://www.stratascratch.com/blog/intersect-vs-union-in-sql): INTERSECT vs UNION in SQL: choose the wrong set operator, and the query returns a plausible but incorrect result, with no error and no warning to tell you so.
- [The AI Ponzi Scheme: Slap on a Chatbot, Raise Millions, Leave Engineers Holding the Bag](https://www.stratascratch.com/blog/the-ai-ponzi-scheme-slap-on-a-chatbot-raise-millions-leave-engineers-holding-the-bag): Everyone's chasing AI riches, but when the bubble bursts, engineers, not investors, will be left cleaning up the mess.
- [Python List Length: How to Find the Size of a List in Python](https://www.stratascratch.com/blog/python-list-length-how-to-find-the-size-of-a-list-in-python): One-stop shop for product data scientists to brush up on the size of the list in Python - a core fundamental that’s an element of many key interview patterns.
- [How To Pass Data Interviews for Machine Learning Engineer Roles](https://www.stratascratch.com/blog/how-to-pass-data-interviews-for-machine-learning-engineer-roles): How do you get a machine learning engineer job? By passing the interviews, obviously. In this article, we deal with exactly that by detailing how to prepare.
- [You Don’t Need to Be a Math Genius for Data Science](https://www.stratascratch.com/blog/you-do-not-need-to-be-a-math-genius-for-data-science): Learn the truth about data science interviews and how deep you actually need to go into maths.
- [How to Use SELECT INTO in SQL for Analytics](https://www.stratascratch.com/blog/how-to-use-select-into-in-sql): SELECT INTO is an often-overlooked tool for analytics. Here we explain its syntax, use cases, how to use it in staging, and how it is tested in interviews.
- [Retention in SQL: How to Calculate User and Cohort Retention?](https://www.stratascratch.com/blog/retention-in-sql-how-to-calculate-user-and-cohort-retention): One-stop shop for product data scientists and job candidates: what is retention and its different types, how to calculate them, with the SQL application.
- [What Is the Role of SQL Substring in Queries?](https://www.stratascratch.com/blog/what-is-the-role-of-sql-substring-in-queries): We explore the use of the SQL SUBSTRING() function to demonstrate its power in analyzing string formats, both for interview preparation and handling data.
- [Simplifying Python’s IF and AND Statements](https://www.stratascratch.com/blog/simplifying-python-s-if-and-and-statements): Python IF and AND statements help you write clear, correct conditional logic by safely combining checks, handling edge cases, and keeping your code readable, efficient, and maintainable.
- [Understanding FLOOR and CEILING Functions in SQL](https://www.stratascratch.com/blog/floor-and-ceiling-functions-in-sql): We explore fundamental concepts of FLOOR and CEILING functions in SQL and demonstrate their value for interview preparation and handling data at scale.
- [How to Use Python Multiprocessing for Better Performance](https://www.stratascratch.com/blog/how-to-use-python-multiprocessing): A quick guide to Python multiprocessing: Speeding up heavy Python tasks by running code in parallel, and knowing when to use threads or async instead.
- [Python Inner Classes: A Guide to Using Class in a Class](https://www.stratascratch.com/blog/python-inner-classes-or-using-class-in-a-class): Inner classes, an advanced form of Python classes, are explained with simple use cases, common mistakes, and best practices.
- [How to Iterate Over a Dictionary in Python?](https://www.stratascratch.com/blog/how-to-iterate-over-a-dictionary-in-python): We explore fundamental concepts in Python ‘Iterate’ over a ‘Dictionary’ (dict) and learn iteration methods to search, update, modify, and transform data.
- [Career Path for Artificial Intelligence Engineers](https://www.stratascratch.com/blog/career-path-for-artificial-intelligence-engineers): Artificial intelligence engineers are a very hot commodity in today's data jobs market. Learn everything you need to know about an AI engineering career.
- [How to Conduct a T-Test in R for Data Analysis](https://www.stratascratch.com/blog/how-to-conduct-a-t-test-in-r): Learn to run t-tests in R: check assumptions, interpret statistical results, and apply insights effectively to real-world data analysis projects.
- [How to Create Pivots in SQL (with examples)](https://www.stratascratch.com/blog/how-to-create-pivots-in-sql): Reshaping data using Pivots is table-stakes in data science. Learn about its importance, techniques, and implementation.
- [Creating a Python Linked List Step by Step](https://www.stratascratch.com/blog/python-linked-lists): Build a stack using a Python linked list, understand the logic, memory flow, and interview-ready reasoning behind it.

## Optional

- [Sitemap](https://www.stratascratch.com/sitemap.xml): every article, guide and category, which this file only samples
- [About](https://www.stratascratch.com/about)
- [Contact](https://www.stratascratch.com/contact-us)