C++ || STL || standard template libraries

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                                       C++ STL  1.      Pair :  Syntax :      pair <int,char> p1;     it creates a pair {2,'c'} like this.           pair <int,int> p2;     it creates a pair {2,3} like this .  Basic Code :  #include <bits/stdc++.h> using namespace std; int main() {     // cout<<"hello world\n";     pair <int,int> p1 = {1,2};     cout<<p1.first<< " "<< p1.second<<endl;          pair <int, pair<int ,char>> p2 = {1,{2,'c'}};     cout<<p2.first<<" "<<p2.second.first<<" "<<p2.second.second<<endl;          pair <int,int> arr[] = {{2,3},{4,5},{6,7}};     cout...
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Percentage of users attending the contest || Leetcode solution || simple explanation ||💯💯💯💯✅✅✅🔥🔥🔥🔥

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                        1633. Percentage of Users Attended a Contest


Problem:-

To find the percentage of users attending contest from users and register table 

Link for question :- click here


so we need to use group by contest_id then aggregation is performed on count(register.user_id)

Approach

select count(*)
from users

This will get the total count of the table in users is 3.

count(register.user_id)

At first group by is done on contest_id (multiple rows to single row) and aggregation is done on count(register.user_id)

SQL Solution :- 

# Write your MySQL query statement below

select register.contest_id , 
round(count(register.user_id)*100/(select count(*) from users),2) as percentage
from users inner join register 
on users.user_id = register.user_id
group by contest_id
order by percentage desc, contest_id asc;

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