mysql - 使用 MAX 函数连接三个表

Question

我有三个表:student、subject 和 score。
我想显示每个学生的 max(subject_id) 的详细信息。

学生表

student_id   student_name  exam_date
   1            Sharukh     24/06/12
   2            Amir        23/06/12

主题表

subject_id    sub_name
   200         Maths
   300         English
   400         Science

评分表

student_id   subject_id     score
    1           200         50 
    1           300         20
    2           300         10

结果应该是:

student_id    student_name     subject_id      score
     1          Sharukh           300            20
     2          Amir              300            10

Answer 1

使用 MAX 函数和 GROUP BY 您的其他选择。

SELECT st.student_id, st.student_name, MAX(su.subject_id) AS subject_id, sc.score
FROM student st
INNER JOIN score sc ON st.student_id = sc.student_id
INNER JOIN subject su ON sc.subject_id = su.subject_id
WHERE su.subject_id = (SELECT MAX(sca.subject_id) 
                       FROM score sca 
                       WHERE sc.student_id = sca.student_id 
                       GROUP BY sca.student_id)
GROUP BY st.student_id, st.student_name, sc.score

输出:

student_id  student_name  subject_id  score
1           Sharukh       300         20
2           Amir          300         10

SQL fiddle :http://sqlfiddle.com/#!9/71c46a/7/0

没有 GROUP BY

SELECT st.student_id, st.student_name, su.subject_id, sc.score
FROM student st
INNER JOIN score sc ON st.student_id = sc.student_id
INNER JOIN subject su ON sc.subject_id = su.subject_id
WHERE su.subject_id = (SELECT MAX(sca.subject_id) 
                       FROM score sca 
                       WHERE sc.student_id = sca.student_id 
                       GROUP BY sca.student_id)