リンク

https://www.hackerrank.com/challenges/the-report/problem?isFullScreen=true

問題の説明

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.

入力例

出力例

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)

コード#コード#

SELECT 
CASE
    WHEN Grades.grade<8 THEN 'NULL'
    ELSE Students.name
    END,
    Grades.grade, 
    Students.marks
FROM Students
INNER JOIN Grades
ON Students.Marks>=Grades.Min_mark and Students.Marks<=Grades.Max_mark 

ORDER BY Grades.grade DESC, Students.name ASC,Students.marks ASC

解説

ON条件は、==のみならず、他の不等式であってもよい.min_mark<=mark<=max_mark相当のGradesとStudentsの内部接続を行うとmark相当のgradeが得られる.

CASE WHENGrades.grade<8はNULLとして表される.