HackerRank: The Report
You are given two tables: Students and Grades. Students contains three columns ID, Name and Marks.
Grades contains the following data:
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
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:
So, the following students got 8, 9 or 10 grades:
- Maria (grade 10)
- Jane (grade 9)
- Julia (grade 9)
- Scarlet (grade 8)
Solution
For the task I’ve decided to use “case” statement and tinker a little with joins.
Case:
case when g.grade >= 8 then s.name
else NULL
END AS Names
A little fun with joins:
from students s
inner join grades g
on g.max_mark >= s.marks and s.marks >= g.min_mark
The Complete Querry:
select
case when g.grade >= 8 then s.name
else NULL
END AS Names
, g.grade, s.marks
from students s
inner join grades g
on g.max_mark >= s.marks and s.marks >= g.min_mark
order by g.grade desc, s.name asc, s.marks asc;
The Output:
Britney 10 95
Heraldo 10 94
Julia 10 96
Kristeen 10 100
Stuart 10 99
Amina 9 89
Christene 9 88
Salma 9 81
Samantha 9 87
Scarlet 9 80
Vivek 9 84
Aamina 8 77
Belvet 8 78
Paige 8 74
Priya 8 76
Priyanka 8 77
NULL 7 64
NULL 7 66
NULL 6 55
NULL 4 34
NULL 3 24
Works for MS SQL and MySQL compilers.