I went straight to the obvious schema (user_id, timestamp, event_type, plan_type) and felt good about it.
Start by clarifying the business requirements and the need for point-in-time accuracy, then propose an event-sourced schema that captures all subscription state changes as immutable events. Explain how to reconstruct status for any date by replaying events up to that date, and discuss handling edge cases like cancellations and re-signups.
Pro tip: Emphasize that using event timestamps and a slowly changing dimension (SCD) Type 2 approach can simplify point-in-time queries, and mention the importance of idempotency and late-arriving data in production systems.
Ask about the granularity needed (daily, real-time), data sources, and whether the schema should support analytics or operational use. Confirm that the goal is to reconstruct status for any date, including multiple subscription lifecycles.
Propose a fact table of subscription events with columns like user_id, event_type (signup, cancel, reactivate), event_timestamp, plan_id, and effective_date. Ensure each event is immutable and has a unique event_id.
Explain how to derive status for a given date by selecting the latest event per user before that date. For example, if the latest event is 'cancel', status is inactive; if 'signup' or 'reactivate', status is active.
Discuss handling of cancellations with future effective dates, backdated events, and multiple signups. Suggest using effective_date to determine when the event takes effect, and consider a status history table for performance.
Mention building a daily snapshot table or using window functions to precompute status, and indexing on user_id and event_timestamp. Discuss trade-offs between storage and query speed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.