percentile_disc vs percentile_cont

Question

PERCENTILE_DISC和PERCENTILE_CONT之间的区别是什么，

我有一个表### select * from childstat

FIRSTNAME                                          GENDER BIRTHDATE     HEIGHT     WEIGHT
-------------------------------------------------- ------ --------- ---------- ----------
lauren                                             f      10-JUN-00         54        876 
rosemary                                           f      08-MAY-00         35        123 
Albert                                             m      02-AUG-00         15        923 
buddy                                              m      02-OCT-00         15        150 
furkar                                             m      05-JAN-00         76        198 
simon                                              m      03-JAN-00         87        256 
tommy                                              m      11-DEC-00         78        167 

我试着区分这些百分位数

select firstname,height,
       percentile_cont(.50) within group (order by height) over() as pctcont_50_ht,
       percentile_cont(.72) within group (order by height) over() as pctcont_72_ht,
       percentile_disc(.50) within group (order by height) over () as pctdisc_50_ht,
       percentile_disc(.72) within group (order by height) over () as pctdisc_72_ht
from childstat order by height


FIRSTNAME                                              HEIGHT PCTCONT_50_HT PCTCONT_72_HT PCTDISC_50_HT PCTDISC_72_HT
-------------------------------------------------- ---------- ------------- ------------- ------------- -------------
buddy                                                      15            54         76.64            54            78 
Albert                                                     15            54         76.64            54            78 
rosemary                                                   35            54         76.64            54            78 
lauren                                                     54            54         76.64            54            78 
furkar                                                     76            54         76.64            54            78 
tommy                                                      78            54         76.64            54            78 
simon                                                      87            54         76.64            54            78 

但是仍然无法理解这两个函数是如何实现的，以及这两个函数的用途是什么。

Answer 1

PERCENTILE_DISC在集合/窗口中返回一个值，而PERCENTILE_CONT将进行插值；

在查询中，当您使用.72时，PERCENTILE_CONT会在76和78之间进行插值，因为72%不是其中之一；PERCENTILE_DISC选择76 (其中最低的一个)

Answer 2

我发现这个解释很有帮助，http://mfzahirdba.blogspot.com/2012/09/difference-between-percentilecont-and.html

    ITEM REGION             WK FORECASTQTY
    ---- ---------- ---------- -----------
    TEST E                   3         137
    TEST E                   2         190
    TEST E                   1         232
    TEST E                   4         400



SELECT
   t.* ,
   PERCENTILE_CONT(0.5)
   WITHIN GROUP ( ORDER BY forecastqty)
   OVER (PARTITION BY ITEM , region ) AS PERCENTILE_CONT ,
   MEDIAN(forecastqty)
   OVER (PARTITION BY ITEM , region ) AS MEDIAN ,
   PERCENTILE_DISC(0.5)
   WITHIN GROUP ( ORDER BY forecastqty)
   OVER (PARTITION BY ITEM , region ) AS PERCENTILE_DISC
   FROM
   t ;



    ITEM REGION             WK FORECASTQTY PERCENTILE_CONT     MEDIAN PERCENTILE_DISC
    ---- ---------- ---------- ----------- --------------- ---------- ---------------
    TEST E                   3         137             211        211             190
    TEST E                   2         190             211        211             190
    TEST E                   1         232             211        211             190
    TEST E                   4         400             211        211             190