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

之前的答案并不完全正确 - 你不会得到有两个具有相同计数的实例。试试这个 - 一旦理解了这个概念，第二个就很容易复制。

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)

替代查询： SELECT a.subject_id，s.subject_name，COUNT（a.subject_id）FROM assignment a，subject s WHERE a.subject_id = s.subject_id GROUP BY a.student_id，s.subject_name HAVING COUNT（a.subject_id）=（SELECT MAX（COUNT（1））FROM FROM GROUP BY subject_id）

SQL：获取具有列（逐列）的行为MAX值的行

1 个答案: