awesome-leetcode-sql/leetcode/easy/1633. Percentage of Users Attended a Contest.sql at 1fda3c8f3e22670ad69e447b51e915e88a60506d · Ivanbyone/awesome-leetcode-sql · GitHub

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/*
Question 1633. Percentage of Users Attended a Contest
Link: https://leetcode.com/problems/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  | int     |
| user_id     | int     |
+-------------+---------+
(contest_id, user_id) is the primary key (combination of columns with unique values) for this table.
Each row of this table contains the id of a user and the contest they registered into.


Write a solution to find the percentage of the users registered in each contest rounded to two decimals.

Return the result table ordered by percentage in descending order. In case of a tie, order it by contest_id in ascending order.
*/

SELECT
    contest_id,
    ROUND(COUNT(contest_id) * 1.0 / (SELECT COUNT(u.user_id) FROM Users AS u) * 100, 2) AS percentage
FROM Register
GROUP BY contest_id
ORDER BY percentage DESC, contest_id ASC