[HackerRank] Advanced Select > Occupations

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.

 

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.

 

 

[MySQL Solution 1]

set @r1=0, @r2=0, @r3=0, @r4=0;
select min(Doctor), min(Professor), min(Singer), min(Actor)   -- min 대신 max도 가능
from(
  select case when Occupation='Doctor' then (@r1:=@r1+1)
            when Occupation='Professor' then (@r2:=@r2+1)
            when Occupation='Singer' then (@r3:=@r3+1)
            when Occupation='Actor' then (@r4:=@r4+1) end as RowNumber,
            
    case when Occupation='Doctor' then Name end as Doctor,
    case when Occupation='Professor' then Name end as Professor,
    case when Occupation='Singer' then Name end as Singer,
    case when Occupation='Actor' then Name end as Actor
  from OCCUPATIONS
  order by Name
	) temp
group by RowNumber;

참고:

https://www.hackerrank.com/challenges/occupations/forum/comments/731399  

https://stackoverflow.com/questions/1009954/mysql-variable-vs-variable-whats-the-difference

 

 

 

[MySQL Solution 2]

SELECT min(Doctor), min(Professor), min(Singer), min(Actor)
FROM (SELECT ROW_NUMBER() OVER (
    	PARTITION BY OCCUPATION ORDER BY NAME) AS r,
        CASE WHEN Occupation = 'Doctor' THEN Name END AS Doctor,
		CASE WHEN Occupation = 'Professor' THEN Name END AS Professor,
		CASE WHEN Occupation = 'Singer' THEN Name END AS Singer,
		CASE WHEN Occupation = 'Actor' THEN Name END AS Actor
	FROM OCCUPATIONS
    ) t
GROUP BY t.r

 

[MySQL Solution 3]

SELECT
    GROUP_CONCAT(if(Occupation = 'Doctor', Name, NULL)) AS 'Doctor', 
    GROUP_CONCAT(if(Occupation = 'Professor', Name, NULL)) AS 'Professor', 
    GROUP_CONCAT(if(Occupation = 'Singer', Name, NULL)) AS 'Singer', 
    GROUP_CONCAT(if(Occupation = 'Actor', Name, NULL)) AS 'Actor'
FROM
(
    SELECT a.*,
        (CASE @vOccup WHEN a.OCCUPATION THEN @rownum:=@rownum+1 ELSE @rownum:=1 END) rnum, -- CASE WHEN @vOccup = a.OCCUPATION THEN ... 도 가능
        (@vOccup:=a.OCCUPATION) vOccup
    FROM OCCUPATIONS a,(SELECT @vOccup:='', @rownum:=0 FROM DUAL) b
    ORDER BY OCCUPATION, NAME ) c
GROUP BY c.rnum

참고: https://mia-dahae.tistory.com/82

SELECT @vOccup:='', @rownum:=0 FROM DUAL;

 

 

 

문제 링크:

https://www.hackerrank.com/challenges/occupations/problem