Concurrent Active Subscriptions Peak

Find the timestamp and count of peak concurrent subscriptions. Intervals are half-open [start_at,end_at): an ending subscription is inactive before another starts at the same timestamp, so end events sort before starts. NULL end_at remains active. Return the earliest timestamp reaching the global peak. Return columns: peak_at, peak_active_subscriptions.

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Challenge overview

What you will practice

Find the timestamp and count of peak concurrent subscriptions. Intervals are half-open [start_at,end_at): an ending subscription is inactive before another starts at the same timestamp, so end events sort before starts. NULL end_at remains active. Return the earliest timestamp reaching the global peak. Return columns: peak_at, peak_active_subscriptions.

Difficulty: Expert
SQL concept: CTE