如何計算最終總金額和百分比

Question

在下面的查詢中，我具有每種語言的學生說的第一語言的總數

CTE

WITH Lang AS
(
    SELECT  
        language, 
        studentcount,
        SUM(Studentcount) AS total
    FROM    
        (SELECT 
             l.longtext AS language,
             COUNT(distinct s.studentnr) AS Studentcount
         FROM 
             student s
         JOIN
             pupil p on p.id = s.pupilid
         JOIN
             pupillanguage pl on pl.personid = p.id
         JOIN
             language l on l.id = pl.languageid
         GROUP BY 
             l.longtext
         ORDER BY 
             Studentcount DESC
        ) t 
    GROUP BY 
        language, Studentcount
)

詢問

SELECT initcap(language), Studentcount, total
FROM Lang 

UNION ALL

SELECT cast(count(language) as varchar(6)) ||' Languages', null, null
FROM Lang

現在我有1個主要問題，這是分配學生的TOTAL SUM值。 我需要這個，所以我可以計算出一列中學生人數/總學生人數的百分比 。 但是，很明顯，我的總價值沒有滿足我的需求。

輸出量

    languages   students    total
    ------------------------------
    French        734        734
    Afrikaans      93         93
    Greek         117        117
    German         55         55
    Armenian      160        160
    Malaysian       5          5
    Danish         15         15
    American        5          5
    Swedish        24         24
    Bulgarian     1043      1043

預期產量：

languages   students    Percentage
-----------------------------------
French        734          24,46
Afrikaans      93           3,12
Greek         117           3,9
German         55           1,83
Armenian      160           5,33
Malaysian       5           0,16
Danish         15           0,5
American        5           0,16
Swedish        24           0,8
Bulgarian     1043         34,76

如何計算最終的總和作為一個數值來計算百分比

Answer 1

demo：db <>小提琴

您可以使用窗口函數（ https://www.postgresql.org/docs/current/static/tutorial-window.html ）：

SELECT
    language,
    students,
    SUM(students) OVER () as total,
    students::decimal / SUM(students) OVER () * 100 as percentage 
FROM
--- <YOUR QUERY>

窗口函數SUM(students) OVER ()匯總了學生列的所有值，因為在OVER子句中沒有給出限制幀

::decimal強制轉換對於獲得浮點除法（100/200 = 0.5）而不是整數除法（100/200 = 0）是必需的。

Answer 2

你可以嘗試如下

with t1 as (           
        SELECT l.longtext as language,
       count(distinct s.studentnr) as Studentcount    
            FROM student s
                join pupil p on p.id = s.pupilid    
                join pupillanguage pl on pl.personid = p.id
                join language l on l.id = pl.languageid    
            group by l.longtext
            order by Studentcount desc
        ) select language,Studentcount, sum(Studentcount) over() as total,
      (Studentcount::float/sum(Studentcount) over())*100 as percentage
      from t1