[MySQL] 해커랭크 Occupations

문제

Pivot the Occupation column in OCCUPATIONS so that each Name is sorted alphabetically and displayed underneath its corresponding Occupation. 

The output column headers should be Doctor, Professor, Singer, and Actor, respectively.

Note: Print NULL when there are no more names corresponding to an occupation.
Input Format

The OCCUPATIONS table is described as follows:

Occupation will only contain one of the following values: Doctor, Professor, Singer or Actor.

 

https://www.hackerrank.com/challenges/occupations/problem?isFullScreen=true

Occupations | HackerRank

예시

Sample Input

Sample Output

Jenny    Ashley     Meera  Jane
Samantha Christeen  Priya  Julia
NULL     Ketty      NULL   Maria

Explanation
The first column is an alphabetically ordered list of Doctor names.
The second column is an alphabetically ordered list of Professor names.
The third column is an alphabetically ordered list of Singer names.
The fourth column is an alphabetically ordered list of Actor names.
The empty cell data for columns with less than the maximum number of names per occupation (in this case, the Professor and Actor columns) are filled with NULL values.

문제 풀이

SELECT 
    MIN(CASE WHEN occupation = 'doctor' THEN name END),
    MIN(CASE WHEN occupation = 'professor' THEN name END),
    MIN(CASE WHEN occupation = 'singer' THEN name END),
    MIN(CASE WHEN occupation = 'actor' THEN name END)
FROM (
    SELECT 
        occupation,
        name, 
        ROW_NUMBER() OVER (PARTITION BY occupation ORDER BY name) as rn
    FROM
        occupations
) AS tmp
GROUP BY 
    rn
ORDER BY 
    rn

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SQL을 독학하시는 분들에게 도움이 되길 바라며,

혹 더 좋은 방법이 있거나 오류가 있다면 편하게 말씀 부탁드립니다.