mysql - 如何使用具有默认值的分组依据？

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     |
+-----------+------------+-------+

我想获得每个学生的分数总和，但需要包括每个学生的类(class)分数。换句话说，我想要一个如下的结果表:

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

实际上，quiz_type 列并不存在。我需要执行 GROUP BY Student_id，但在每个组中包含 NULL 值。我已经为此苦苦挣扎了很长一段时间。有什么好的解决办法吗？

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