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Introduction To SQL
SQL stands for Structured Query Language. SQL is used to create, remove, alter the database and database objects in a database management system and to store, retrieve, update the data in a database. SQL is a standard language for creating, accessing, manipulating database management system. SQL works for all modern relational database management systems, like SQL Server, Oracle, MySQL, etc.
- It is a standard language for Relational Database System. It enables a user to create, read, update and delete relational databases and tables.
- All the RDBMS like MySQL, Informix, Oracle, MS Access and SQL Server use SQL as their standard database language.
- SQL allows users to query the database in a number of ways, using English-like statements.
Link for the Problem – Challenges SQL – Hacker Rank Solution
Challenges SQL – Hacker Rank Solution
Problem:
Julia asked her students to create some coding challenges. Write a query to print the hacker_id, name, and the total number of challenges created by each student. Sort your results by the total number of challenges in descending order. If more than one student created the same number of challenges, then sort the result by hacker_id. If more than one student created the same number of challenges and the count is less than the maximum number of challenges created, then exclude those students from the result.
Input Format
The following tables contain challenge data:
- Hackers: The hacker_id is the id of the hacker, and name is the name of the hacker.
- Challenges: The challenge_id is the id of the challenge, and hacker_id is the id of the student who created the challenge.
Sample Input 0
Hackers Table: 
Challenges Table: 
Sample Output 0
21283 Angela 6 88255 Patrick 5 96196 Lisa 1
Sample Input 1
Hackers Table:Challenges Table:
Sample Output 1
12299 Rose 6 34856 Angela 6 79345 Frank 4 80491 Patrick 3 81041 Lisa 1
Explanation
For Sample Case 0, we can get the following details:
Students and both created challenges, but the maximum number of challenges created is so these students are excluded from the result.
For Sample Case 1, we can get the following details:
Students and both created challenges. Because is the maximum number of challenges created, these students are included in the result.
Challenges SQL – Hacker Rank Solution
SELECT H.HACKER_ID,
H.NAME,
COUNT(C.CHALLENGE_ID) AS TOTAL
FROM HACKERS H,
CHALLENGES C
WHERE H.HACKER_ID=C.HACKER_ID
GROUP BY H.HACKER_ID,
H.NAME
HAVING COUNT(C.CHALLENGE_ID) IN
(SELECT MAX(TOTAL)
FROM
(SELECT COUNT(*) AS TOTAL
FROM CHALLENGES
GROUP BY HACKER_ID))
OR COUNT(C.CHALLENGE_ID) IN
(SELECT TOTAL
FROM
(SELECT COUNT(*) AS TOTAL
FROM CHALLENGES
GROUP BY HACKER_ID)
GROUP BY TOTAL
HAVING COUNT(TOTAL)=1)
ORDER BY COUNT(C.CHALLENGE_ID) DESC, H.HACKER_ID;
