我有以下表格:
CREATE TABLE Subject
(
Subject_Code INTEGER,
Subject_Year VARCHAR (8),
PRIMARY KEY (Subject_Code, Subject_Year),
Teacher_ID INTEGER REFERENCES
);
CREATE TABLE Teacher
(
TeacherID INTEGER PRIMARY KEY,
FirstName TEXT,
Department_ID INTEGER References Academic Department(Department_ID)
);
CREATE TABLE Subject-taken
(
Marks_Obtained INTEGER,
Subject_Code INTEGER REFERENCES subject (Subject_Code),
Candidate_ID INTEGER REFERENCES Candidate (Candidate_ID),
PRIMARY KEY (Subject_Code, Candidate_ID)
);
CREATE TABLE Academic_Department
(
Department_ID INTEGER PRIMARY KEY,
Department_Name TEXT
);
我已经尝试过以下选择语句
SELECT m.subject_code,
MIN (marks_obtained) AS Min_Marks,
MAX (marks_obtained) AS Max_Marks
FROM Subject-taken m, Subject a
GROUP BY m.Subject_Code;
想要使用连接功能关于在何处使用它以连接学科和学生的部门的任何建议
最佳答案
利用联接在表之间链接数据。使用 group by 对某些字段进行统计。你可以尝试这样的事情:
SELECT
Subjects.Subject_Code,
Subjects.Subject_Name,
Teachers.TeacherID,
Academic_Department.Department_ID,
min(Subject-taken.Marks_Obtained) as min_marks,
max(Subject-taken.Marks_Obtained) as max_marks,
avg(Subject-taken.Marks_Obtained) as avg_marks,
stddev_samp(subject-taken.Marks_Obtained) as stddev_marks
FROM
Subjects LEFT JOIN
Teachers ON Subjects.TeacherID = Subjects.TeacherID LEFT JOIN
Academic_Department ON Teachers.Department_ID = Academic_Department.Department_ID LEFT JOIN
Subject-taken ON Subjects.Subject_Code = Subject-taken.Subject_Code
GROUP BY
Subjects.Subject_Code,
Subject.Subject_Name,
Teacher.TeacherID,
Academic_Department.Department_ID
我真的不知道stddev_samp
是不是你需要的聚合函数,stddev_pop
也可以。请引用this PostgreSQL documentation table找出答案。
关于sql - 适当的 SELECT 语句,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55535602/