Occupations

Advanced SELECT

Question Link

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.

/*
The MAX (or MIN) is needed so that MySQL fills in the unique column value when 
scanning across the 4 values per row in the cte (Common Table Expression), 
not necessarily in the column order required.
Removal of the aggregation MAX (or MIN) leads to a syntax error, which I believe 
is due to violation of 2NF (2nd normal form), as there must be some dependence
of these attributes on the key n.
*/


WITH cte AS (
    SELECT 
        Name, 
        Occupation,
        ROW_NUMBER() OVER (PARTITION BY Occupation ORDER BY Name) AS n
    FROM Occupations
)

SELECT 
    MAX(IF(occupation="Doctor",name,NULL)) as Doctor,
    MAX(IF(occupation="Professor",name,NULL)) as Professor,
    MAX(IF(occupation="Singer",name,NULL)) as Singer,
    MAX(IF(occupation="Actor",name,NULL)) as Actor
FROM cte 
GROUP BY n;