##### Question You are given two tables describing LinkedIn members’ push-notification settings. Compute each member’s **current notification status as of `2020-02-29`** by combining the end-of-January baseline with the toggle actions recorded during February. ### Tables `status` — each member’s **latest setting as of `2020-01-31`** - `member_id` INT - `status` VARCHAR — `'on'` or `'off'` `actions` — all notification-toggle actions taken during **February 2020** - `member_id` INT - `action_date` DATE — a UTC calendar date between `2020-02-01` and `2020-02-29` - `action` VARCHAR — `'turn_on'` or `'turn_off'` ### Assumptions - A member performs **at most one action per day**. - Every `actions` row occurs **after** the `2020-01-31` snapshot. - `actions` may include **new members not present in `status`** (e.g., a member created after `2020-01-31`). ### Tasks 1. Return each member’s **current notification status as of `2020-02-29`**. - Include **every member who appears in either table** — members only in `status`, members only in `actions`, and members in both. - If a member has at least one February action, their status is determined by their **latest** February action (`turn_on` → `'on'`, `turn_off` → `'off'`). - If a member has no February action, their status remains the `status` value from `2020-01-31`. - Output columns: `member_id`, `current_status`. 2. **Follow-up A — no date column.** Suppose `actions` no longer contains `action_date`, so you cannot order the actions. Explain whether the final status can still be reconstructed, and specify what additional data, assumptions, or table design would be required to make the problem solvable. 3. **Follow-up B — no date column, valid-transition guarantee.** Now add the assumption that every recorded action is a **valid state transition** from the member’s previous state (a `turn_on` only ever follows an `'off'` state and vice versa, so no contradictory or repeated actions occur). Under that guarantee, describe (or write SQL for) how you would infer the final status as of `2020-02-29` using only the snapshot plus the **multiset** of February actions for each member.