Solve it in your browser. Share your time. Come back next week. 138 challenges in rotation, picked deterministically each week — same challenge for everyone, no leaderboard gaming.
Find all unique countries that orders have been placed from. Show just the country column with no duplicates. Sort alphabetically. Then, in a second approach, count how many unique countries there are (as country_count).
Past challenges are still solvable in the app. Each week's pick is deterministic, so anyone visiting that week sees the same challenge — fair time comparisons.
Practicing SQL works the way going to the gym works: a small, predictable habit beats heroic sprints. 15 minutes every Monday for a year is enough to clear most data-analyst SQL interviews. A scattered hour-here-and-there approach plateaus around month 2.
The Weekly Challenge is the ritual. Same time every week, fresh problem, no decision fatigue. Solve it, share it if you want to, come back Monday. The practice bank of 300+ challenges is here when you want unlimited; the weekly is for when you want a single committed rep.
SQL Quest's free tier gives you 10 free challenge solves — any Easy or Medium, or one of the 6 Hard previews — plus the lessons, warm-ups, the daily challenge and the AI Coach with a daily quota.
Open SQL Quest — Free ⚡Or: learn SQL from zero · interview prep hub · tutorials blog