我如何查询路口 table

Question

您好，我正在尝试查询路口 table，但我无法弄明白。我怎样才能找到在特定课程中得分最高的五个学生

 CREATE TABLE Students (
 StudentID int NOT NULL PRIMARY KEY,
 LastName varchar(255) NOT NULL,
 FirstName varchar(255) NOT NULL,
 StudentNum int NOT NULL,
);
CREATE TABLE Courses (
 CourseID int NOT NULL PRIMARY KEY,
 CourseName varchar(255) NOT NULL,
 GPA int(255) NOT NULL
);

CREATE TABLE University (
StudentID int NOT NULL,
CourseID int NOT NULL,
CONSTRAINT PK_University PRIMARY KEY
(
StudentID,
CourseID
),
FOREIGN KEY (StudentID) REFERENCES Students (StudentID),
FOREIGN KEY (CourseID) REFERENCES Courses (CourseID)
);

Answer 1

我将分数字段添加到 University table 并将大学名称更改为 Students_Courses。

首先将大学table改为：

CREATE TABLE Students_Courses (
 StudentID int NOT NULL,
 CourseID int NOT NULL,
 Score float,
 CONSTRAINT PK_Students_Courses PRIMARY KEY
 (
 StudentID,
 CourseID
 ),
 FOREIGN KEY (StudentID) REFERENCES Students (StudentID),
 FOREIGN KEY (CourseID) REFERENCES Courses (CourseID)
);

现在您可以 join table 并按分数排序并找到最高分中的 5 个。

你可以使用

select top 5 s.StudentID,s.FirstName,s.LastName,sc.Score,c.CourseName
from Students_Courses sc join Students s on sc.StudentID = s.StudentID
join Courses c on sc.CourseID = c.CourseID
where sc.CourseID = 1
order by Score desc

或

select top 5 s.StudentID,s.FirstName,s.LastName,sc.Score 
from Students_Courses sc join Students s on sc.StudentID = s.StudentID
where sc.CourseID = 1
order by Score desc

或使用window函数

select StudentID,FirstName,LastName,Score 
from
  (select s.StudentID,s.FirstName,s.LastName,sc.Score,ROW_NUMBER() over(order by sc.Score desc) as seq
  from Students_Courses sc join Students s on sc.StudentID = s.StudentID
  where sc.CourseID = 1) T
where seq <= 5

演示在 dbfiddle

我如何查询路口 table

How can I query junction table

sql

junction