Fetch·Data Scientist·Technical Phone Screen
Jul 2026
Fetch Data Scientist interview with a SQL question focused on rolling averages over sparse time series data. The calendar-day window requirement is the part that trips people up.
- Given a table of daily product metrics where some dates may be missing, write a SQL query using window functions to compute the 7-day rolling average of daily active users. The window must be based on calendar-day distance, not row count.
“The row-count vs calendar-day distinction is what makes this non-trivial.”