sql多表查询分组最大值

时间:2023-02-05 20:07:30

问题描述:有三张表:学生表Student(id,name),id为主键;课程表Subject(id,name),id为主键;分数表score(studentid,subjectid,score),其中studentId与subjectid为联合主键,一句sql语句查询出:学号,姓名,课程名,课程最高分.

模拟实现如下:

三张表:

CREATE TABLE student
(
id INT PRIMARY KEY AUTO_INCREMENT,
`name` VARCHAR(20)
)
CREATE TABLE subjects(  id INT PRIMARY KEY AUTO_INCREMENT,  `name` VARCHAR(20))
CREATE TABLE score(  studentid INT REFERENCES student(id),  subjectid INT REFERENCES subjects(id),  score INT,  PRIMARY KEY(studentid,subjectid))
模拟插入的数据如下:

INSERT INTO student VALUES(NULL,'zhangSan');
INSERT INTO student VALUES(NULL,'liSi');
INSERT INTO subjects VALUES(NULL,'Chinese');
INSERT INTO subjects VALUES(NULL,'English');
INSERT INTO score VALUES(1,1,60);
INSERT INTO score VALUES(1,2,90);
INSERT INTO score VALUES(2,1,70);
INSERT INTO score VALUES(2,2,80);

每个人解题都有自己的思路,我说一下我自己的思路:我认为难点在于要分组查询出每个学科的最高分,所有要先对score表进行查询,结果为每一个subjectid对应一个最高的score。首先,我想到的思路就是:得到相同学科的最高分数,再查询score表,找到最高分数的记录,代码如下:

SELECT * FROM score a WHERE score=(SELECT MAX(score) FROM score WHERE subjectid=a.subjectid)
只要做到这,相信剩下的就没有什么难度了,就是简单的多表查询了,不多说了,直接上完整的代码

SELECT st.id,st.name,sj.name,sc.score FROM student st,subjects sj,
(SELECT * FROM score a WHERE score=(SELECT MAX(score) FROM score WHERE subjectid=a.subjectid)) sc
WHERE st.id = sc.studentid AND sj.id = sc.subjectid

每个人的想法不一样,做法就不一样,如果大家有更好的解决办法,欢迎大家留言讨论!

快乐学习,快乐编程!