SQL百分比計算原始表

Question

我使用SQL有一個問題：

我有一個表：

School Name | Class | Studends 
=================================== 
Golden  | 1  | 20 
Red   | 1  | 80 
Golden  | 2  | 7 
Red   | 2  | 14 
Golden  | 3  | 3 
Red   | 3  | 1 

我想有以下結果：

School Name | Class | Percent  
====================================== 
Golden  | 1  | 20 % 
Red   | 1  | 80 % 
Golden  | 2  | 33 % 
Red   | 2  | 66 % 
Golden  | 3  | 75 % 
Red   | 3  | 25 % 

我試圖找到解決方案，但沒有找到，任何人都有答案？

Answer 1

如果您的RDBMS支持窗口聚集

SELECT 
    School_Name, 
    Class, 
    100.0 * Studends/SUM(Studends) OVER (PARTITION BY Class) AS Percent 
FROM YourTable 

Answer 2

SELECT 
    a."School Name", 
    a.Class, 
    a.Studends/SUM(b.Students) 
FROM YourTable a 
LEFT JOIN YourTable b ON a.Class = b.Class 
GROUP BY 
    a."School Name", 
    a.Class, 
    a.Studends, 
    b.Class