Question

我正在努力寻找可以报名参加课程的剩余学生。为此，我需要找到目前活跃且目前不在课程中的学生。我认为我写的查询是不正确的，因为当我运行查询时，它会一直显示一组空的结果，如何才能找到能够参加课程的剩余学生？

以下是当前查询：

SELECT  st.StudentId, StudentAlias, StudentForename, StudentSurname
FROM    Course c
        INNER JOIN Student_Course sc
            ON c.CourseId = sc.CourseId
        INNER JOIN Student st
            ON sc.StudentId = st.StudentId
WHERE   (c.CourseId = 1 AND
        sc.StudentId IS NULL
        AND st.Active = 1)
ORDER   BY st.StudentAlias

以下是表格：

学生：（所有学生名单）

StudentId  StudentAlias  StudentForename  StudentSurname  Active
1          u09382        James            Smith           1
2          u83923        John             Brooks          1
3          u38292        Karen            Bradshaw        0
4          u20039        Chris            Cameron         1
5          u39399        Jane             Fields          1

课程：（所有课程列表）

CourseId  CourseNo  CourseName
1         INFO121   ICT
2         BUS122    Business and Finance
3         ENG432    English Language

Student_Course：（参加各自课程的学生名单）

StudentId  CourseId
1          1
1          3
2          1
4          2
5          2

因此，例如，如果我选择CourseId = 1，那么它应该显示有效但但显然不在CourseId = 1的学生，这意味着它应该向下方显示这些学生注册课程的可能性：< / p>

4 - Chris Cameron
5 - Jane Fields

Answer 1

尝试此查询

SELECT s.studentId, s.Forename
FROM Student s
WHERE s.studentId NOT IN (SELECT studentId 
FROM  Student_Course c WHERE c.courseId = 1) AND s.Active = 1

内部子查询返回courseId = 1的学生，在外部查询中我们过滤那些学生。

Answer 2

试试这个

SELECT  st.StudentId, StudentAlias, StudentForename, StudentSurname
FROM    Course c
        INNER JOIN Student_Course sc
            ON c.CourseId = sc.CourseId
        INNER JOIN Student st
            ON sc.StudentId = st.StudentId
WHERE   (sc.CourseId <> 1
        AND st.Active = 1)
ORDER   BY st.StudentAlias

Answer 3

要找到不在课程上的活跃学生，请选择以下内容： -

SELECT  st.StudentId, StudentAlias, StudentForename, StudentSurname
FROM    Student st
LEFT OUTER JOIN Student_Course sc ON sc.StudentId = st.StudentId
LEFT OUTER JOIN Course c ON c.CourseId = sc.CourseId
WHERE   c.CourseId IS NULL
AND st.Active = 1
ORDER   BY st.StudentAlias

如果你想检查没有参加特定课程的学生，那么

SELECT  st.StudentId, StudentAlias, StudentForename, StudentSurname
FROM    Student st
LEFT OUTER JOIN Student_Course sc ON sc.StudentId = st.StudentId
LEFT OUTER JOIN Course c ON c.CourseId = sc.CourseId AND CourseId = 1
WHERE   c.CourseId IS NULL
AND st.Active = 1
ORDER   BY st.StudentAlias

让课程检查ON条款

如何编写正确的查询以查找当前未在课程中的学生

3 个答案: