Time Between Events — Solution & ExplanationProblems / Time Between Events / EditorialApproach

Window function: Use LAG(event_date) OVER (PARTITION BY user_id ORDER BY event_date) to get each user's previous event date.

Calculate difference: Use DATEDIFF('day', prev_event_date, event_date) to get days between consecutive events.

Filter: Exclude rows where prev_event_date is NULL (each user's first event).

Key ConceptThe LAG() window function accesses the value from a previous row without requiring a self-join. Combined with DATEDIFF, it provides an efficient way to compute inter-event intervals.Hints

Use the LAG() window function partitioned by user_id and ordered by event_date.

DATEDIFF('day', prev_date, current_date) gives the gap in days.

Filter out rows where the previous date is NULL.

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