Таблица subscribers содержит user_id, plan (basic/premium), start_date. Таблица activity содержит user_id, activity_date. Сравните Day-7 и Day-14 retention между планами basic и premium. Выведите plan, total_users, ret_d7_pct, ret_d14_pct.
CREATE TABLE subscribers (user_id INTEGER PRIMARY KEY, plan TEXT, start_date TEXT);
CREATE TABLE activity (user_id INTEGER, activity_date TEXT);
RETENTION GROUP BY CASE DATE PLAN COMPARISON