如何在SQL中将单个表视为多个表

Question

我从Hackerrank.com示例输入遇到了这个SQL挑战：

select * from occupation 

样本输出：

Name        Occupation     
samantha    doctor
jenny       doctor
julia       actor
maria       actor
jane        actor
meera       singer
priya       singer
ashley      professor
ketty       professor
christeen   professor

输出应为：（医生，教授，歌手，演员也应按姓名排序）

jenny       ashley         meera       jane
samantha    christeen      priya       julia
null        ketty          null        maria

我试过的是：

SELECT DECODE(occupation,'doctor',name,NULL   ),DECODE(occupation,'professor',name,NULL),DECODE(occupation,'singer',name,NULL)  ,
DECODE(occupation , 'actor',name,NULL)
FROM occupation ;

但这并没有给我想要的结果。

SELECT oc1.name ,
oc2.name,oc3.name,oc4.name
FROM
(SELECT name,occupation FROM occupation WHERE occupation = 'doctor'
) oc1 ,
(SELECT name,occupation FROM occupation WHERE occupation = 'actor'
) oc2 ,
(SELECT name,occupation FROM occupation WHERE occupation = 'singer') oc3,
(SELECT name,occupation FROM occupation WHERE occupation = 'professor')oc4  ,   occupation oc

WHERE 
oc1.occupation= oc.occupation(+)
and oc2.occupation = oc.occupation(+)
AND oc3.occupation       = oc.occupation(+)
AND oc4.occupation       = oc.occupation(+);

但是它给出了重复的记录。 有人可以帮帮我吗

谢谢

Answer 1

使用PIVOT ：

SELECT doctor, professor, singer, actor
FROM   (
  SELECT o.*,
         ROW_NUMBER() OVER ( PARTITION BY occupation ORDER BY name ) AS rn
  FROM   occupation o
)
PIVOT ( MAX( name ) FOR Occupation IN (
  'doctor'    AS doctor,
  'actor'     AS actor,
  'singer'    AS singer,
  'professor' AS professor
) )
ORDER BY rn;