Find each user's longest streak of consecutive active days in SQL (gaps and islands).
Consecutive-run problems (active streaks, uptime windows, price-stable periods) all boil down to one trick. Once the row-number difference clicks, they collapse to a window function and a group-by.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
Consecutive-run problems (active streaks, uptime windows, price-stable periods) all boil down to one trick. Once the row-number difference clicks, they collapse to a window function and a group-by.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
