SQL Valid Event and Anomaly Counts

Tell me about a time you handled tricky data manipulation issues, including edge cases and unexpected input, in a production system.

For a hands-on SQL follow-up, use the users and production_events tables. Treat supported event types as valid only when their timestamp is present and their value is either nonnegative or NULL.

Output

1. One row per user, including users with no events
2. Columns: user_id, email, valid_event_count, anomaly_count, and latest_valid_at
3. Exclude unknown users from the result, count invalid known-user events as anomalies, and sort by user_id ascending

Output details

• Treat session_started, session_ended, and note_created as the only supported event types.
• Count qualifying events only when event_id is non-NULL, without deduplicating event rows.
• Report valid_event_count and anomaly_count as 0 when no counted events exist.
• Set latest_valid_at to NULL when no valid event exists.