Question

SELECT  students.student_name, courses.course_name, grades.grade
FROM students, student_enrollment, grades, courses
WHERE students.id=student_enrollment.student_id 
AND student_enrollment.id=grades.student_enrollmet_id 
AND student_enrollment.course_id=courses.id

使用MS Access我试图获取学生姓名和每个科目的平均成绩（课程名称）。当我尝试添加＆＃34; SELECT AVG（students.student_name，courses.course_name，grades.grade）＆＃34;它不起作用。

Answer 1

SELECT 
    s.student_name, c.course_name, avgGrades.resultGrade
FROM 
    ((SELECT 
        se.course_id, se.student_id, AVG(g.grade) AS resultGrade
    FROM
        grades g
    INNER JOIN student_enrollment se ON g.student_enrollment_id = se.id
    GROUP BY se.course_id, se.student_id) avgGrades
INNER JOIN students s ON avgGrades.student_id = s.id)
INNER JOIN courses c ON avgGrades.course_id = c.id

尝试在连接多个表时从一个表中获取AVG

1 个答案: