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1633. Percentage of Users Attended a Contest.md

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1633. Percentage of Users Attended a Contest

Question Link

First we'll see a wrong one and explanation then we'll see a right one ;-)

WEONG Code

# Write your MySQL query statement below
select r.contest_id, round(count(distinct r.user_id)*100/count(user_id), 2) percentage
from Register r left join Users u
on u.user_id=r.user_id group by r.contest_id ORDER BY percentage DESC, contest_id

Why wrong: The dividend (or the denominator) is wrong. It is not the User table's countnumber but the new table's.

RIGHT Code

# Write your MySQL query statement below
select r.contest_id, round(count(distinct r.user_id)*100/(select count(user_id) from Users), 2) percentage
from Register r left join Users u
on u.user_id=r.user_id group by r.contest_id ORDER BY percentage DESC, contest_id
  • 2024.06.02