Analyze Multiple-Account Users in SQL

You are analyzing a product in which a single user can own multiple accounts. Use the following tables: **accounts** - `account_id` BIGINT — unique account ID - `user_id` BIGINT — owner of the account - `created_at` TIMESTAMP — when the account was created - `last_visit_at` TIMESTAMP — most recent time the user visited that account **notifications** - `notification_id` BIGINT — unique notification ID - `account_id` BIGINT — account that received the notification - `sent_at` TIMESTAMP — when the notification was sent - `read_at` TIMESTAMP NULL — when the notification was read; `NULL` means unread Assumptions: - Each account belongs to exactly one user. - A user may have one or more accounts. - All timestamps are stored in UTC. - For these questions, use the current state of the tables; no additional time window is required. Write SQL for the following: 1. Using only the `accounts` table, return the number of users who have exactly 2 accounts, exactly 3 accounts, and 4 or more accounts. - Required output columns: - `account_bucket` (`'2'`, `'3'`, or `'4+'`) - `user_count` 2. Among users who have 2 or more accounts, compute the percentage of users who have at least one unread notification across any of their accounts. - An unread notification is defined as `read_at IS NULL`. - Required output column: - `pct_multi_account_users_with_unread_notifications` as a decimal between 0 and 1.