Question

您好我正在使用mysql在学校数据库上工作。我坚持查询以返回得分最高的学生。我尝试了不同的查询组合，但没有一个能够工作。一些学生返回所有100年级的学生（注意我的一个学生在测试数据中只有100年级）和其他返回的第一个学生在测试数据中有100年级。我怀疑我的数据库中有错误但我无法解决。< / p>

DB：

CREATE TABLE Student
(
StudentID INT  auto_increment,
ClassID VARCHAR(10),
FirstName VARCHAR(25),
LastName VARCHAR(25),
DateOfBirth DATE,
Gender VARCHAR(10),
PRIMARY KEY (StudentID, ClassID)
);

create table Subjects
(
SubjectID INT,
SubjectName VARCHAR(25),
PRIMARY KEY (SubjectID)
);



create table Grade
(
StudentID INT,
SubjectID INT,
ClassID VARCHAR(10),
Grade DECIMAL(5,1),
FOREIGN KEY (StudentID) REFERENCES Student(StudentID),
FOREIGN KEY (SubjectID) REFERENCES Subjects(SubjectID),
FOREIGN KEY (ClassID) REFERENCES Student(ClassID)
);



Test data:
INSERT INTO Student (StudentID, ClassID, FirstName, LastName, DateOfBirth, Gender)
VALUES ('', '01', 'John', 'Smith', '15/01/2000', 'Male'),
('', '01', 'Michael', 'Black', '15/03/2000', 'Male'),
('', '01', 'Dennis', 'White', '07/08/1999', 'Male'),
('', '01', 'Emy', 'Blue', '10/04/2000', 'Female'),
('', '01', 'Joe', 'Yellow', '09/05/2000', 'Male'),
('', '01', 'Aaren', 'Jackson', '09/009/1999', 'Male'),
('', '01', 'Marta', 'Harris', '30/01/2000', 'Female'),
('', '01', 'Laura', 'Lewis', '09/01/2000', 'Female'),
('', '01', 'Michael', 'Jackson', '01/01/2000', 'Male'),

('', '02', 'Piotr', 'Kowalski', '15/01/2000', 'Male'),
('', '02', 'Harris', 'Bialy', '15/03/2000', 'Male'),
('', '02', 'Porter', 'Czarny', '07/08/1999', 'Male'),
('', '02', 'Maciek', 'Blue', '10/04/2000', 'Female'),
('', '02', 'Mateusz', 'Yellow', '09/05/2000', 'Male'),
('', '02', 'Aaren', 'Jackson', '09/009/1999', 'Male'),
('', '02', 'Marta', 'Harris', '30/01/2000', 'Female'),
('', '02', 'Laura', 'Lewis', '09/01/2000', 'Female'),
('', '02', 'Chaytan', 'Jackson', '01/01/2000', 'Male');


INSERT INTO Subjects (SubjectID, SubjectName)
VALUES ('01', 'English'),
('02', 'Mathematics'),
('03', 'Science'),
('04', 'Geography'),
('05', 'IT'),
('06', 'History');

INSERT INTO Grade (StudentID, SubjectID, ClassID, Grade)
VALUES ('01', '1', '01', '60.5'),
('01', '2', '01', '70.0'),
('01', '3', '01', '40.0'),
('01', '4', '01', '33.5'),
('01', '5', '01', '90.0'),
('01', '6', '01', '77.5'),
('01', '7', '01', '89.0'),
('01', '8', '01', '74.0'),
('01', '9', '01', '66.5'),

('01', '10', '02', '30.5'),
('01', '11', '02', '50.0'),
('01', '12', '02', '30.0'),
('01', '13', '02', '73.5'),
('01', '14', '02', '70.0'),
('01', '15', '02', '57.5'),
('01', '16', '02', '69.0'),
('01', '17', '02', '34.0'),
('01', '18', '02', '76.5'),

('02', '1', '01', '65.5'),
('02', '2', '01', '73.0'),
('02', '3', '01', '41.0'),
('02', '4', '01', '39.5'),
('02', '5', '01', '96.0'),
('02', '6', '01', '70.5'),
('02', '7', '01', '80.0'),
('02', '8', '01', '74.0'),
('02', '9', '01', '64.5'),

('02', '10', '02', '55.5'),
('02', '11', '02', '43.0'),
('02', '12', '02', '61.0'),
('02', '13', '02', '49.5'),
('02', '14', '02', '76.0'),
('02', '15', '02', '80.5'),
('02', '16', '02', '99.0'),
('02', '17', '02', '100.0'),
('02', '18', '02', '55.5');

你知道我哪里出错了吗？你能告诉我适当的查询来检索得分最高的学生吗？感谢

Answer 1

我认为这就是你想要的，这将使你获得每个科目得分最高的学生，如果你想要一个特定的科目，你可以将WHERE SubjectID=Subjects.SubjectID改为WHERE SubjectID=particular_subject_id

SELECT Student.FirstName, Subjects.SubjectName, Grade.Grade, Subjects.SubjectID FROM 
Student INNER JOIN Grade ON Grade.StudentID=Student.StudentID 
INNER JOIN Subjects ON Grade.SubjectID=Subjects.SubjectID WHERE Grade.Grade=
(SELECT MAX(Grade) FROM Grade WHERE SubjectID=Subjects.SubjectID)

平均值：

 SELECT Subjects.SubjectName, AVG(Grade.Grade), Grade.ClassID, Subjects.SubjectID 
 FROM Grade INNER JOIN Subjects ON Grade.SubjectID=Subjects.SubjectID
 GROUP BY Grade.ClassID, Grade.SubjectID;

这是一个有效的fiddle，可以查看最高得分和平均值的结果。

Answer 2

您应该尝试这个也是正确答案：

SELECT 
A.FirstName, 
C.SubjectName, 
B.Grade, 
C.SubjectID 
FROM Student AS A
INNER JOIN Grade AS B ON B.StudentID=A.StudentID 
INNER JOIN Subjects AS C ON B.SubjectID=C.SubjectID 
WHERE B.Grade=(SELECT MAX(Grade) FROM Grade WHERE SubjectID=C.SubjectID)

fiddle

Answer 3

如果我理解你的话，那么这样的事情应该有效：

select s.* from Students s
    join Grades g on a.StudentID = s.StudentID
where s.StudentID = (select max(Grade) from Grades);

MYSQL数据库查询返回最高分

3 个答案: