Find the percentage of the users registered in each contest rounded to two decimals. Return the result table ordered by percentage in descending order and contest_id in ascending order.
This challenge now meets the current minimum standard for sitemap inclusion and independent indexing.
Find the percentage of the users registered in each contest rounded to two decimals. Return the result table ordered by percentage in descending order and contest_id in ascending order.
This is a denominator-selection problem. Teams frequently misstate metrics by using the wrong population baseline, and contest participation, feature adoption, and campaign reach all depend on comparing a subgroup against the correct total population.
user_iduser_namecontest_iduser_idSELECT
contest_id,
ROUND(COUNT(user_id) * 100.0 / (SELECT COUNT(*) FROM users), 2) AS percentage
FROM register
GROUP BY contest_id
ORDER BY percentage DESC, contest_id ASCThis is the shortest correct solution. The subquery provides the total user population once, and each contest group divides its registration count by that same denominator.
WITH totals AS (
SELECT COUNT(*) AS total_users
FROM users
)
SELECT
r.contest_id,
ROUND(COUNT(r.user_id) * 100.0 / t.total_users, 2) AS percentage
FROM register r
CROSS JOIN totals t
GROUP BY r.contest_id, t.total_users
ORDER BY percentage DESC, r.contest_id ASCThe CTE version is useful when the denominator becomes more complex later, such as active users only or users from a filtered segment. It keeps the baseline population explicit and auditable.
A common mistake is dividing by the number of registrations in the same contest instead of by the total number of users. Another is forgetting decimal multiplication, which can cause integer truncation and return 0 or a rounded-down percentage.
Because the metric asks what percentage of all users registered for each contest. Total registrations answers a different question and would make every contest look artificially complete.
It maps to feature adoption and participation metrics: how much of a total user population engaged with a specific event, campaign, or product feature.
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