如何使用默认值分组？

Question

假设我有下表：

+-----------+------------+-------+
| quiz_type | student_id | score |
+-----------+------------+-------+
| class     | NULL       | 10    |
+-----------+------------+-------+
| class     | NULL       | 9     |
+-----------+------------+-------+
| student   | A          | 5     |
+-----------+------------+-------+
| student   | B          | 7     |
+-----------+------------+-------+
| student   | A          | 6     |
+-----------+------------+-------+

我想得到每个学生的分数总和，但需要包括每个学生的课程分数。换句话说，我想要一个结果表，如：

+------------+-------+
| student_id | score |
+------------+-------+
| A          | 30    |
+------------+-------+
| B          | 26    |
+------------+-------+

实际上，quiz_type列不存在。我需要执行GROUP BY student_id，但每个组都包含NULL值。我一直在努力解决这个问题。有一个很好的解决方案吗？

Answer 1

你可以试试这个：

select 
    student_id,
    sum(score) + (select sum(score) from yourtable where student_id is null) as score
from yourtable
where student_id is not null
group by `student_id`

SQLFiddle Demo