Write activation and funnel SQL

Help me write activation and funnel SQL.
Inputs: event table; metrics; dialect.

1. Define deduplication and stage-entry rules.
2. handle ordering, duplicates and day boundaries.
3. provide queries with stage-count validation.

Deliver: Definitions, Query, Edge cases handled, Check it, Questions.
Clarify critical gaps, separate facts from assumptions, and do not invent data, citations or completed actions.

My material: [fill in here]

事前準備

Provide event table; metrics; dialect.