Impute, join, and upsert using SQL and Python

We are given a small slice of a subscription-analytics warehouse. Four tables describe who signed up, what they did, a landing area that receives freshly exported events, and the payments that were collected. Wherever a task refers to a "recent" window, treat 2025-09-01 as the current date. For every part below, produce two implementations: one SQL query and one pandas solution. Also state the indexing or keying choices you make (which columns you treat as primary keys, what…