SQL：获取具有一列（按列分组）为最大值的行

Question

我想知道如何检索与列的最大值匹配的行。

SCHEMA

assignments:
id  student_id   subject_id
1   10           1
2   10           2
3   20           1
4   30           3
5   30           3
6   40           2

students:
id  name
10   A
20   B
30   C

subjects:
id  name
1   Math
2   Science
3   English

查询：提供以下SQL：

1. Display the names of the students who have taken most number of assignments
2. Display the names of the subjects which have been taken the most number of times

结果：

1. 
  A
  C

2. 
  Math
  English

谢谢 ！

Answer 1

先前的答案不太正确-您将不会获得其中两个具有相同计数的实例。 尝试一下-一旦理解了概念，第二个将很容易复制。

SELECT a.student_id, s.name, COUNT(a.subject_id) as taken_subjects
FROM assignments a
INNER JOIN students s ON a.student_id = s.id
GROUP BY a.student_id, s.name
HAVING COUNT(a.subject_id) = (SELECT COUNT(*) FROM assignments GROUP BY student_id LIMIT 1)

备用查询：从任务a中选择a.subject_id，s.subject_name，COUNT（a.subject_id），主题s。从赋值GROUP BY subject_id中选择SELECT MAX（COUNT（1））