MySQL таблица "Pivot" без создания таблиц / представлений: уникальные значения столбца в качестве заголовка

Question

У меня есть таблица из двух столбцов «Профессии», в которой указаны имя и профессия нескольких человек.Профессии известны и могут быть только «Разработчик», «Инженер», «Доктор», «Музыкант».

Name   | Occupation
Dan    | Developer
Martin | Doctor
Sam    | Engineer
Andre  | Musician
Tom    | Engineer

Цель состоит в том, чтобы получить что-то вроде следующего:

Doctor | Engineer | Developer | Musician
Martin |    Sam   |   Dan     |  Andre
NULL   |    Tom   |   NULL    |   NULL

Все столбцы должны быть упорядочены в алфавитном порядке.

У вас есть какие-либо предложения относительно того, как мне этого добиться (без создания таблиц, представлений) с помощью MySQL?

Большое спасибо!

Answer 1

Это будет работать в MySql 8.0:

with occup as (
select
  case when o.occupation = 'Doctor' then o.Name end as Doctor, 
  case when o.occupation = 'Engineer' then o.Name end as Engineer,
  case when o.occupation = 'Developer' then o.Name end as Developer,  
  case when o.occupation = 'Musician' then o.Name end as Musician
from occupations o
),

doctors as (
select ROW_NUMBER() OVER (
 ORDER BY case when occup.Doctor is null then 1 else 0 end
 ) as rn, occup.Doctor from occup
),
engineers as (
select ROW_NUMBER() OVER (
 ORDER BY case when occup.Engineer is null then 1 else 0 end
 ) as rn, occup.Engineer from occup
),
developers as (
select ROW_NUMBER() OVER (
 ORDER BY case when occup.Developer is null then 1 else 0 end
 ) as rn, occup.Developer from occup
),
musicians as (
select ROW_NUMBER() OVER (
 ORDER BY case when occup.Musician is null then 1 else 0 end
 ) as rn, occup.Musician from occup
)

select doctors.Doctor, engineers.Engineer, developers.Developer, musicians.Musician 
from doctors
inner join engineers on doctors.rn = engineers.rn  
inner join developers on engineers.rn = developers.rn
inner join musicians on musicians.rn = developers.rn
WHERE coalesce(doctors.Doctor, engineers.Engineer, developers.Developer, musicians.Musician) IS NOT NULL;

См. Демоверсию

Answer 2

Это боль, но вы можете сделать это с помощью переменных и агрегации:

select max(doctor) as doctor,
       max(engineer) as engineer,
       max(developer) as developer,
       max(musician) as musician
from ((select name as doctor, null as engineer, null as developer, null as musician,
              (@rnd := @rnd + 1) as rn
       from t cross join
            (select @rnd := 0) as params
       where occupation = 'doctor'
      ) union all
      (select null as doctor, name as engineer, null as developer, null as musician,
              (@rne := @rne + 1) as rn
       from t cross join
            (select @rne := 0) as params
       where occupation = 'engineer'
      ) union all
      (select null as doctor, null as engineer, name as developer, null as musician,
              (@rnv := @rnv + 1) as rn
       from t cross join
            (select @rnv := 0) as params
       where occupation = 'developer'
      ) union all
      (select null as doctor, null as engineer, null as developer, name as musician,
              (@rnm := @rnm + 1) as rn
       from t cross join
            (select @rnm := 0) as params
       where occupation = 'musician'
      ) union all
     ) o
group by rn;