如何计算每位老师教的学生人数？

Question

我有一个包含以下表格的数据库

Courses: CourseID*, CourseName, TeacherID
Teachers: TeacherID*, TeacherName
Students: StudentID*, StudentName
StudentCourses: CourseID*, StudentID*

图例： *是主键。

如何写出产生的查询产生每位老师教授的学生人数？

例如

TeacherName, Count
Bob 15
Sarah 5
Zubair 1

编辑

select "TeacherName", count(*)
from courses inner join teachers on courses."TeacherID" = teachers."TeacherI"
join sutdentcourses on sutdentcourses."CourseID" = courses."CourseID"
group by "TeacherName"
order by "TeacherName";

Answer 1

您需要在教师，课程和学生课程表之间建立联接，按教师名称对记录进行分组并计算学生ID。

SELECT TeacherName, COUNT(StudentID)
FROM Teachers JOIN Courses USING(TeacherID)
JOIN StudentCourses USING(CourseID)
GROUP BY TeacherName