計算研究區域的百分比

Question

我需要生成SQL數據庫的幫助。

我有兩個表：

• 學生
• student_Subjects

學生表：

 
+------------+---------+-----------------+ 
| id  | name |area_of_study_id | 
+------------+---------+-----------------+ 
| 1   | AAA  | 1    | 
| 2   | BBB  | 2    | 
| 3   | CCC  | 1    | 
| 4   | DDD  | 3    | 
| 5   | EEE  | 4    | 
| 6   | FFF  | 1    | 
| 7   | GGG  | 2    | 
| 8   | III  | 1    | 
+------------+---------+-----------------+ 

student_subjects表：

 
+------------+-------------------+------------------+ 
| id  | student_id  | subject_id  | 
| 1   | 1     |  1   | 
| 2   | 2     |  1   | 
| 3   | 1     |  3   | 
| 4   | 1     |  2   | 
| 5   | 3     |  1   | 
| 6   | 6     |  1   | 
| 7   | 7     |  3   | 
| 8   | 4     |  6   | 
+------------+-------------------+------------------+ 

我需要找出基於students area of study一個subject's area of study。從學生表上可以看到，學生可以自由選擇area of study。有時，他們可以選擇與其學習領域無關的科目。因此，在這種情況下，我們需要根據已採納主題的student percentages來計算area of study的subject。

的部分輸出：

 
+------------+-------------------+-----------------------------------+ 
|Total_students | subject_id |area_of_study_id | percentage  | 
+------------+-------------------+-----------------+-----------------+ 
| 3   | 1     | 1    | 75    | 
| 1   | 1     | 2    | 25    | 
| 1   | 3     | 1    | 50    | 
| 1   | 3     | 2    | 50    | 
| 1   | 2     | 1    | 100    | 
| 1   | 6     | 3    | 100    | 
+------------+-------------------+-----------------+-----------------+ 

從上面的部分輸出中，我們可以看到，3名學生選擇的受試者（即subject_id = 1）具有研究1的面積和一個學生是來自不同區研究（即2）。所以，我們可以說subject_id =1是從area of study = 1。

如果百分比50％爲一個主題。我們可以選擇兩個之間的任何學習領域，不管是哪一個。

預期輸出：

 
+------------+-------------------+-----------------------------------+ 
|Total_students | subject_id |area_of_study_id | percentage  | 
+------------+-------------------+-----------------+-----------------+ 
| 3   | 1     | 1    | 75    | 
| 1   | 3     | 1    | 50    | 
| 1   | 2     | 1    | 100    | 
| 1   | 6     | 3    | 100    | 
+------------+-------------------+-----------------+-----------------+ 

在先進的感謝。

Answer 1

嘗試這種方式

SELECT subject_id, area_of_study_id, total_students, percentage 
    FROM 
(
    SELECT p.subject_id, p.area_of_study_id, p.total_students, 
     p.total_students/t.total_students * 100 percentage 
    FROM 
    (
    SELECT COUNT(*) total_students, ss.subject_id, s.area_of_study_id 
     FROM students s JOIN student_subjects ss 
     ON s.id = ss.student_id 
    GROUP BY ss.subject_id, s.area_of_study_id 
) p JOIN 
    (
    SELECT ss.subject_id, COUNT(*) total_students 
     FROM students s JOIN student_subjects ss 
     ON s.id = ss.student_id 
    GROUP BY ss.subject_id 
) t ON p.subject_id = t.subject_id 
    ORDER BY percentage DESC 
) q 
    GROUP BY subject_id; 

輸出：

 
| SUBJECT_ID | AREA_OF_STUDY_ID | TOTAL_STUDENTS | PERCENTAGE | 
|------------|------------------|----------------|------------| 
|   1 |    1 |    3 |   75 | 
|   2 |    1 |    1 |  100 | 
|   3 |    1 |    1 |   50 | 
|   6 |    3 |    1 |  100 | 

這裏是SQLFiddle演示