1633. Percentage of Users Attended a Contest

Table: Users +-------------+---------+ | Column Name | Type | +-------------+---------+ | user_id | int | | user_name | varchar | +-------------+---------+ user_id is the primary key (column with unique values) for this table. Each row of this table contains the name and the id of a user. Table: Register +-------------+---------+ | Column Name | Type | +-------------+---------+ | contest_id |