SQL for Data Science Interviews — From Basics to Advanced

SQL is the most tested skill in every data science technical screen — and the one where candidates lose the most points, not because they don't know SQL, but because they make small syntax mistakes under pressure or structure queries in a way that doesn't communicate their thinking.

This guide covers everything you need to walk in confident:

✅ Core SQL concepts — GROUP BY, HAVING, JOINs, CTEs, CASE WHEN, COALESCE, NULLIF

✅ Window functions — RANK, ROW_NUMBER, DENSE_RANK, LAG/LEAD, running totals

✅ 12 progressive practice questions on the real Instacart dataset — with full answers and key learnings

✅ The pre-submit checklist — run through this before every query in an interview

✅ The 10 most common SQL mistakes and exactly how to fix them

✅ Full setup guide for Jupyter Notebook with the Instacart Kaggle dataset

Built by a Senior Data Scientist with 13+ years of experience at Mastercard, the Ministry of Finance, and major Canadian institutions, and practiced before a real senior DS technical screen.

19 pages. No filler. Just what actually matters.