求和2列并使用DESC对其进行排序，仅显示1条记录，首先插入优先级（最小的id）

您好我知道我的实际问题看起来有点复杂，

所以首先我有 student

+------------+------- +---------+
| id_student | score_a|score_b  |
+------------+--------+---------+
| 1          | 70     |80       |
+------------+--------+---------+
| 2          | 70     |90       |
+------------+--------+---------+
| 3          | 80     |70       |
+------------+--------+---------+
| 4          | 80     |70       |
+------------+--------+---------+
| 5          | 80     |90       |
+------------+--------+---------+
| 6          | 60     |70       |
+------------+--------+---------+
| 7          | 60     |80       |
+------------+--------+---------+
| 8          |40      |70       |
+------------+--------+---------+

那么 class

+----------+--------------+
| id_class | limit_people |
+----------+--------------+
| 1        | 2            |
+----------+--------------+
| 2        | 2            |
+----------+--------------+
| 3        | 1            |
+----------+--------------+

最后一个让我们说 register . 在这个表上，学生可以选择2个 class ，但是当它按照2个分数（ student.score_a 和 student.score_b ）DESC的总和按顺序排序时，它们只能在1个类（首先插入是优先级）（基于 class.limit_people 字段的限制）（这是均匀的）可能吗？），我知道这是否正确 . 我希望你能为此提供更好的领域/专栏

register

+-------------+-------------+----------+
| id_register | id_students | id_class |
+-------------+-------------+----------+
| 1           | 1           | 1        |
+-------------+-------------+----------+
| 2           | 1           | 2        |
+-------------+-------------+----------+
| 3           | 2           | 2        |
+-------------+-------------+----------+
| 4           | 2           | 3        |
+-------------+-------------+----------+
| 5           | 3           | 1        |
+-------------+-------------+----------+
| 6           | 3           | 3        |
+-------------+-------------+----------+
| 7           | 4           | 3        |
+-------------+-------------+----------+
| 8           | 4           | 2        |
+-------------+-------------+----------+

我使用的当前查询是

SELECT register.id_register, register.id_students, SUM((student.score_a*50/100)+ (student.score_b*50/100)) as total,register.id_class 
FROM `register` LEFT JOIN `student` ON register.id_students=student.id_student 
GROUP by register.id_register ORDER BY total DESC

这就是结果

+-------------+-------------+-------+----------+
| id_register | id_students | total | id_class |
 +-------------+-------------+-------+----------+
| 3           | 2           | 80    | 2        |
+-------------+-------------+-------+----------+
| 4           | 2           | 80    | 3        |
+-------------+-------------+-------+----------+
| 2           | 1           | 75    | 2        |
+-------------+-------------+-------+----------+
| 5           | 3           | 75    | 1        |
+-------------+-------------+-------+----------+
| 6           | 3           | 75    | 3        |
+-------------+-------------+-------+----------+
| 7           | 4           | 75    | 3        |
+-------------+-------------+-------+----------+
| 8           | 4           | 75    | 2        |
+-------------+-------------+-------+----------+
| 1           | 1           | 75    | 1        |
+-------------+-------------+-------+----------+

你可以看到所有的学生都展示了2次，如果没有总结所有具有相同id_students的 total ，如何优先显示firt插入的id，如果有多个记录具有相同的 register.id_students ，如何使它只有1次？

这是我想要的表格

+-------------+-------------+-------+----------+
| id_register | id_students | total | id_class |
+-------------+-------------+-------+----------+
| 3           | 2           | 80    | 2        |
+-------------+-------------+-------+----------+
| 1           | 1           | 75    | 1        |
+-------------+-------------+-------+----------+
| 5           | 3           | 75    | 1        |
+-------------+-------------+-------+----------+
| 7           | 4           | 75    | 3        |
+-------------+-------------+-------+----------+