A. SQL Grouping and Subquery

A. SQL Grouping and Subquery.md

SQL Grouping and Subquery

Challenge: https://www.hackerrank.com/challenges/contest-leaderboard/problem

Solution by https://www.hackerrank.com/basaks

B. SQL Grouping and Subquery #2.md

SQL Grouping and Subquery #1

https://www.hackerrank.com/challenges/full-score/problem

Solution by: https://www.hackerrank.com/ATMaher

query.sql

select h.hacker_id, h.name, sum(max_score.score) as total_score

from hackers as h 

inner join
    /* find max_score per user/challenge */
    (select hacker_id,  max(score) as score from submissions group by challenge_id, hacker_id) max_score

on h.hacker_id = max_score.hacker_id

group by h.hacker_id, h.name

-- /* don't accept hackers with total_score=0 */
having total_score > 0

-- /* finally order as required */
order by total_score desc, h.hacker_id;

query2.sql

SELECT h.hacker_id, h.name
    FROM submissions s
    JOIN challenges c
        ON s.challenge_id = c.challenge_id
    JOIN difficulty d
        ON c.difficulty_level = d.difficulty_level 
    JOIN hackers h
        ON s.hacker_id = h.hacker_id
    WHERE s.score = d.score 
    GROUP BY h.hacker_id, h.name
    HAVING COUNT(s.hacker_id) > 1
    ORDER BY COUNT(s.hacker_id) DESC, s.hacker_id ASC