Hacker Rank SQL

The Report Solution

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Problem

You are given two tables: Students and Grades. Students contains three columns ID, Name and Marks.

Column Type
ID Integer
Name String
Marks Integer

Grades contains the following data:

Grade Min_Mark Max_Mark
1 0 9
2 10 19
3 20 29
4 30 39
5 40 49
6 50 59
7 60 69
8 70 79
9 80 89
10 90 99

Ketty gives Eve a task to generate a report containing three columns: Name, Grade and Mark. Ketty doesn’t want the NAMES of those students who received a grade lower than 8. The report must be in descending order by grade — i.e. higher grades are entered first. If there is more than one student with the same grade (8-10) assigned to them, order those particular students by their name alphabetically. Finally, if the grade is lower than 8, use “NULL” as their name and list them by their grades in descending order. If there is more than one student with the same grade (1-7) assigned to them, order those particular students by their marks in ascending order.

Write a query to help Eve.

Sample Input

Id Name Marks
1 Julia 88
2 Samantha 68
3 Maria 99
4 Scarlet 78
5 Ashley 63
6 Jane 81

Sample Output

Maria 10 99
Jane 9 81
Julia 9 88 
Scarlet 8 78
NULL 7 63
NULL 7 68

Note: Print “NULL”  as the name if the grade is less than 8.

Explanation

Consider the following table with the grades assigned to the students:

Id Name Marks Grade
1 Julia 88 9
2 Samantha 68 7
3 Maria 99 10
4 Scarlet 78 8
5 Ashley 63 7
6 Jane 81 9

So, the following students got 8, 9 or 10 grades:

  • Maria (grade 10)
  • Jane (grade 9)
  • Julia (grade 9)
  • Scarlet (grade 8)

Solution – The Report

MySQL Code
SELECT CASE
    WHEN G.grade > 7 THEN S.name
    ELSE NULL
    end AS names,
    G.grade,
    S.marks

FROM   students S
    JOIN grades G
    ON S.marks BETWEEN G.min_mark AND G.max_mark

ORDER  BY G.grade DESC,
    names ASC,
    S.marks ASC;

 

 

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