用加法和减法计算累计和

Question

我有给定格式的 table

+----+--------------+-----------+-----------+-----------+------------+
| ID | Student Name | Subject   | Add Marks | Sub Marks | Cumulative |
+----+--------------+-----------+-----------+-----------+------------+
| 1  | Adam         | Physics   |        74 |        15 |         59 |
+----+--------------+-----------+-----------+-----------+------------+
| 2  | Adam         | Chemistry |        62 |        11 |        110 |
+----+--------------+-----------+-----------+-----------+------------+
| 3  | Adam         | Maths     |       100 |        10 |        200 |
+----+--------------+-----------+-----------+-----------+------------+
| 4  | Joel         | Maths     |        90 |        10 |         80 |
+----+--------------+-----------+-----------+-----------+------------+
| 5  | Joel         | Physics   |        80 |        15 |        145 |
+----+--------------+-----------+-----------+-----------+------------+
| 6  | Joel         | Chemistry |        65 |        20 |        190 |
+----+--------------+-----------+-----------+-----------+------------+
| 7  | Zampa        | Physics   |        60 |        15 |         45 |
+----+--------------+-----------+-----------+-----------+------------+

如图所示计算每个学生的累积列累积 + 加分 - 每个学生的子分

Answer 1

您需要 ORDER BY 的密钥才能达到您期望的累积总和。例如，我已将 id 列分配给每条记录，并从 1 开始递增 1，因此样本数据如下所示：

 id | student_name |  subject  | addmark | submark
----+--------------+-----------+---------+--------
  1 | Adam         | Physics   |      74 |      15
  2 | Adam         | Chemistry |      62 |      11
  3 | Joel         | Maths     |      90 |      10
  4 | Joel         | Physics   |      80 |      15
  5 | Zampa        | Physics   |      60 |      15

Table 姓名：students.

然后查询将如下所示：

select
  student_name,
  subject,
  addmark,
  submark,
  addmark - submark
          + coalesce(lag(addmark - submark) over (partition by student_name order by id),0) as cumulative
from students;

我正在使用 window 函数 lag 从上一行获取值（这里是您需要排序的地方），并使用 coalesce 函数正确处理每一行的第一行学生，其中 lag returns null 将其替换为 0，因为添加 null 将 return null。

输出

 student_name |  subject  | addmark | submark | cumulative
--------------+-----------+---------+---------+------------
 Adam         | Physics   |      74 |      15 |         59
 Adam         | Chemistry |      62 |      11 |        110
 Joel         | Maths     |      90 |      10 |         80
 Joel         | Physics   |      80 |      15 |        145
 Zampa        | Physics   |      60 |      15 |         45

注意：如果没有 id 列并且我们决定按 student_name 排序，那么累积会发生变化，因为 Adam | Chemistry 在 Adam | Physics 对之前排序。您可以在此示例中使用降序，但就添加的不同主题而言，这并不能真正解决您的问题。

Answer 2

Kamil 的调整解决方案：

select
  Student_Name,
  Subject,
  Add_Marks,
  Sub_Marks,
  sum(Add_Marks - Sub_Marks)
    over (partition by Student_Name order by ID) as Cumulative
from students;

如果没有 ID 字段，可以使用以下方法为此查询创建一个：

select
  Student_Name,
  Subject,
  Add_Marks,
  Sub_Marks,
  sum(Add_Marks - Sub_Marks)
    over (partition by Student_Name order by ID) as Cumulative
from ( select *,row_number() over () as ID from students ) tmpt ;

顺便说一句，输出就像 OP：

student_name      subject   add_marks   sub_marks   cumulative  
Adam    Physics     74  15  59
Adam    Chemistry   62  11  110
Adam    Maths       100 10  200
Joel    Maths       90  10  80
Joel    Physics     80  15  145
Joel    Chemistry   65  20  190
Zampa   Physics     60  15  45

用加法和减法计算累计和

Calculate cumulative sum with addition and subtraction

postgresql

cumulative-sum