mysql - 只有成绩最好的学生

Question

我在学生和分数之间有一个简单的关系:

学生:

+------------+-------------+
| idStudent  | NameStudent |
+------------+-------------+
|         1  | Student A   |
|         2  | Student B   |
|         3  | Student C   |
+------------+-------------+

标记:

+----------+------+-----------+
| idMarks  | mark | idStudent |
+----------+------+-----------+
|        1 | A    |         1 |
|        2 | A    |         1 |
|        3 | A    |         1 |
|        4 | A    |         2 |
|        5 | A    |         2 |
|        6 | C    |         3 |
|        7 | A    |         3 |
+----------+------+-----------+

我只想让学生在他们通过的每门考试中都获得“A”

SELECT *, COUNT(mark)
FROM student S
INNER JOIN marks M ON S.idStudent = M.idStudent
WHERE M.mark = "A"
GROUP BY S.idStudent

我试过了，但是当我试图比较他们通过的考试数量和他们获得 A 的数量时，我遇到了僵局...

我也试过子查询，但没用

Answer 1

你可以使用HAVING:

SELECT S.idStudent
FROM student S
INNER JOIN marks M ON S.idStudent = M.idStudent
GROUP BY S.idStudent
HAVING COUNT(mark)=SUM(mark='A');-- compare all marks with marks that are only 'A'
                                 -- if equal then every mark is 'A'