Interview Round: Top-N per Group, Nth Highest, Streaks

Answer as you would at a whiteboard, stating tie-handling explicitly.

1. Return each country's top 2 users by total paid revenue.
2. Return the third-highest distinct order amount; return NULL if there is no such value. Show two approaches and say how they differ on ties.
3. Find users who placed a paid order on at least 4 consecutive calendar days, with the start date of each such streak. Explain the date - row_number trick with a tiny example.